Wooden Boat Restoration & Repair

Wooden Boat Restoration & Repair
Wooden Boat Restoration & Repair
A guide to restore the structure, improve the appearance, reduce the maintenance
and prolong the life of wooden boats with WEST SYSTEM® Brand epoxy
1 Introduction
Assess the feasibility of restoration or repair with WEST SYSTEM epoxy
2 Inspecting and Evaluating
Analyze the structure for loss of stiffness, dry rot damage, and repair strategies
3 Repairing Localized Dry Rot
Repair small areas damaged by dry rot
4 Repairing the Structural Framework
Repair or replace damaged frames, beams, stems, sheer clamps and keels
5 Repairing Hull and Deck Planking
Repair damaged carvel, lapstrake, plywood and molded veneer planking
6 Installing Hardware
Install hardware to increase load-carrying capacity and eliminate deck leaks
7 Protecting and Maintaining Wooden Boats
Applying protective coatings for finishing and preserving wooden boats
8 Using WEST SYSTEM epoxy
Use WEST SYSTEM products safely and effectively
Appendix WEST SYSTEM product estimating guides
Problem solving guide
Wood data
Additional reading
Wooden Boat Restoration & Repair
Catalog Number 002-970
6th Edition
A guide to restore the structure, improve the appearance,
reduce the maintenance and prolong the life of wooden boats
with WEST SYSTEM® Brand epoxy
The techniques described in this manual are based on the handling techniques and
physical properties of WEST SYSTEM® Brand epoxy products. Because physical
properties of resins systems and epoxy brands vary, using the techniques in this
publication with coatings or adhesives other than WEST SYSTEM is not
This manual is updated as products and techniques change. If the last copyright date
below is more than several years old, contact your WEST SYSTEM dealer or Gougeon
Brothers, Inc. for a current version.
The information presented herein is believed to be reliable as of publication date, but
we cannot guarantee its accuracy in light of possible new discoveries. Because Gougeon
Brothers, Inc. cannot control the use of WEST SYSTEM Brand products in customer
possession, we do not make any warranty of merchantability or any warranty of fitness
for a particular use or purpose. In no event shall Gougeon Brothers, Inc. be liable for
incidental or consequential damages.
WEST SYSTEM and Gougeon Brothers are registered trademarks; and Microlight and
Episize are trademarks of Gougeon Brothers, Inc., Bay City, Michigan USA.
Copyright © September 1990, December 1992, June 1997, May 1999, September
2000, April 2003 by Gougeon Brothers, Inc. All rights reserved. No part of the
contents of this book may be reproduced or transmitted in any form or by any means
without the written permission of the publisher.
Published by Gougeon Brothers, Inc., PO Box 908, Bay City, MI 48707 USA.
Printed 4/03
Cover photo sequence—Restoration of the 1922 gaff-rigged sloop, REEB by Chris
Table of Contents
1 Introduction
1.1 Assessing the feasibility of repair and restoration
1.2 Why wooden boats fail
1.3 WEST SYSTEM epoxy for wooden boat repair .
1.4 Key steps in repair and restoration .
2 Inspecting and Evaluating
2.1 Understanding the Structure
2.2 Inspecting and locating damaged areas
3 Repairing Localized Dry Rot
2.1 Excavate and fill .
2.2 Drilling and filling
2.3 Reinforcing .
3.1 Laminating beams, frames and stems .
3.2 Removal and replacement of frames .
3.3 Removing and replacing a damaged section
3.4 Installing sister frames or doublers
3.5 Joint repairs .
4 Repairing the Structural Framework
3.6 Repairing garboards .
3.7 Keel repair
4.1 Carvel planked hulls and laid plank decks .
4.2 Lapstrake Planked Hulls .
4.3 Plywood hulls and decks .
4.4 Molded or laminated veneer repairs
4.5 Installing a teak veneer deck .
5 Repairing Hull and Deck Planking
6 Installing Hardware
6.1 Fastener bonding
6.2 Hardware bonding
6.3 Casting epoxy bases for hardware.
6.4 Bonding studs
6.5 Removable hardware.
6.6 Removing bonded hardware .
7 Protecting and Maintaining Wooden Boats
6.1 Sunlight and protective coatings .
6.2 Applying the final epoxy coatings .
6.3 Clear finish coatings .
6.4 Paint
6.5 Repairing dings and cracks
6.6 Ventilation for longevity .
8 Using WEST SYSTEM® Epoxy
8.1 Epoxy safety.
8.2 Epoxy products .
8.3 Handling epoxy .
8.4 Basic techniques .
WEST SYSTEM product estimating guides.
Problem solving guide
Wood data .
Additional reading
1 Introduction
Since the early 1970’s, epoxy has been at the forefront of a revolution in boat building.
Wood has once again become the primary building material for many of today’s
fastest, most durable and most beautiful boats, both sail and power. Many of the
techniques of wood/epoxy construction that have made modern wooden boats so
successful can also be applied to the repair of older wooden boats with excellent
results. Wooden Boat Restoration & Repair explains these techniques, drawing on years
of testing and experience at Gougeon Brothers, Inc. and the experiences of many
individual builders. The manual does not offer cheap, easy or quick fixes, for these are
rarely satisfactory. However, it does offer reliable and thorough information for
restoration and repair, ranging from reinstalling a cleat to rebonding the entire boat.
The technical staff at Gougeon Brothers, Inc. have been helping customers with boat
repair and restoration problems since the epoxy revolution began. Whenever we talk
to someone about a project, we begin by asking the same basic questions:
What type of construction is the boat?
What condition is the boat in?
How will the boat be used?
What results are you looking for? A quick repair, a complete restoration or
something in between?
Are you prepared to commit the time and resources to get the results you’re
looking for?
Is wood/epoxy construction the best solution to your problem?
How can wood/epoxy construction be used effectively for your repair?
Depending on the answers to these questions, we try to help the customer formulate a
reasonable plan of action and determine how wood/epoxy construction and WEST
SYSTEM products might be used. Some of the questions are relatively easy—How was
the boat built? What are the boat’s problem areas? Other questions may be more
difficult to define—what is your commitment to repairing the boat? Naturally, the
larger the boat, the greater the damage or more thorough the restoration, the more
important this question becomes. Wooden Boat Restoration & Repair is set up to help
you answer the above questions for yourself. You owe it to yourself and the project not
to shortchange the process but to consider each question carefully. Only when you
have reasonable answers to all the questions should the real job of repairing or
restoring begin. A careful analysis of these questions and perhaps a review of the
manual and what a repair will involve can also help you decide whether or not to buy a
particular older wooden boat in need of repair.
Using the manual
Wooden Boat Restoration & Repair approaches a repair project in several phases.
Section 1 provides guidelines for assessing the feasibility of repair and restoration,
provides an overview of problems typically encountered in wooden boats and explains
the major uses of epoxy in repair.
Section 2 discusses how you can evaluate the soundness of your boat’s structure and
locate damaged areas.
Sections 3, 4, 5 and 6 provide detailed procedures for the most common types of
repairs. These sections can be used in whatever order your repair requires.
Section 7 discusses how to protect against UV, finish and maintain wooden boats.
Section 8 provides fundamental techniques for using WEST SYSTEM epoxy products
successfully in wooden boat repairs, including surface preparation, bonding, bonding
with fillets, laminating, fairing, applying woven cloth and tape, final coating and
finishing. Particularly if you have not used WEST SYSTEM products before, it is
important to read this section carefully before beginning any of the repairs discussed in
previous sections.
Following the procedures described in Wooden Boat Restoration & Repair will allow
you to restore the primary functions of the boat’s structure, reduce flexing and provide
moisture protection. They will assure thorough, long-lasting repairs for boats or other
wooden structures.
1.1 Assessing the feasibility of repair and
The repair methods in this manual offer practical solutions to structural problems in
wooden boats that are within the abilities of the amateur. However, before embarking
on a major rebuilding operation, it is important to evaluate your commitment carefully
and determine your approach to repair and the time and money you are prepared to
allocate to the project.
1.1.1 Distinguish between repair and restoration
Do you want your boat faithfully restored, repaired to function and look good, or
patched and in the water as quickly as possible?
Repair means to fix broken parts, to patch holes resulting from impact or moisture
damage, to strengthen weak spots or tighten loose parts. If your goal is repair, you do
not need to commit yourself to a consistent repair method. You can fix one part with
epoxy and another part another way. However, you need to consider the effects of a
repair on the overall structure. For example, bonding a plank in place with epoxy
could cause high local stiffness in an otherwise flexible structure. In some cases, it may
be better to repair the boat in the same fashion in which it was built rather than use
different bonding and construction techniques.
Restoration means to bring a boat back to its original (or better than original)
condition. To restore a boat successfully you need to develop an overall approach to
renovation and maintain consistency in reconstruction methods. Any restoration is a
major project that will involve much time, dedication and careful planning.
You need to decide the level of repair that suits you and your boat. Theoretically, no
boat is beyond restoration; realistically, you need to evaluate thoroughly the
soundness of the structure and the time and expense needed for repair. If you have
limited experience with rebuilding, we advise hiring a surveyor before getting heavily
1.1.2 Determine your commitment
Consider these factors when determining your commitment to repair or restore:
Time and resources
Many people have become romantically involved with restoration projects and have
failed to make their dreams a reality. Others have started projects which required far
greater financial and time commitments that they were able to allocate and have been
forced to abandon the project. You need to carefully assess the money and the time that
you have available and can afford to commit. Consider, for example, whether you can
restore specific areas of your craft each year, spreading the work and expense over
time. Do you have adequate space and equipment for the project?
Historical value
If you have a very old boat that you are considering restoring, investigate its
background to see if it has historical or collector’s value. If you have an Adirondack
guideboat, an old wood and canvas canoe, a Herreshoff, a Rushton or some other
historically significant boat, wholesale repairs with epoxy may not be appropriate. You
owe it to yourself and the boat to do some research into the boat’s value.
Condition of the boat
Obviously, the worse the condition of the boat, the more work needed to repair it.
While in theory no boat is beyond restoration, you should probably think about
looking for another boat if less than 60 percent of the boat is salvageable.
Size of the craft
Reconstruction difficulty increases with boat size. This is because larger craft
experience higher loads. Boat timbers are proportional to boat size and epoxy is
usually just on a surface or perimeter. This means epoxy strengths and effects can be
overwhelmed by proportionately larger wood mass effects. Dimensional changes can
be the result of moisture passage or temperature cycling as well as stresses from boat
use. Also larger craft may have more areas that are difficult or impossible to access.
Construction method
You need to understand the construction method originally used to build the boat and
the level of difficulty involved with repair of different construction methods. The
following provides a general guide to the logistical and practical ease of reconstructing
craft built using different construction methods, with the easiest listed first:
Plywood (soft and hard chine)
Strip plank
Laminated (hot and cold molded)
Carvel (single)
Carvel (double)
If you have little experience with boat repair, reading the rest of this manual can give
you some sense of the work involved in particular projects. You will also need to make
a thorough evaluation of the boat’s structure as described in Section 2 or hire a
surveyor. Try to talk to others who have undertaken similar projects. Understanding
your own level of commitment to the project and developing a realistic plan for repair
and restoration are necessary for your project to succeed.
1.2 Why wooden boats fail
The nature of wood and the techniques required to build boats in the past have
contributed to both the beauty and the misfortune of wooden boats. The amount of
work necessary to maintain wooden boats tarnished their appeal, and lack of
maintenance resulted in many beautiful wooden boats being devoured by the elements.
Wooden boats may vary widely in age and condition, but most suffer in some degree
from two common problems.
1.2.1 Loss of stiffness
Much of the appeal of wooden boats lies in the boatbuilder’s skill in joining many
individually crafted pieces of wood into a single structure and loss of the original stiffness
is a major cause of a boat’s deterioration. The forces acting on a boat during normal use
put each joint under a continual strain. For example, when a wave or swell passes under a
boat, it lifts the hull unevenly. Waves supporting the hull under the ends force the sides
of the hull apart; a wave supporting the hull in the middle forces the sides together.
Waves or swells crossing at an angle can lift the bow in one direction and the stern in
another, causing a twist that pulls one side of the hull and deck forward and the other
side aft. Other loads come from lifting the boat for storage, adding cargo and stressing
the rigging under sail. Thus, a boat is under a constant state of twisting, stretching and
flexing. All of the joints must resist this flexing to keep the structure rigid and watertight.
The smallest movement around a fastener can weaken the fastener’s holding power,
leading to more flexibility. Over time, every exterior joint that can flex is a potential
source of moisture penetration. Traditional caulking methods are intended to flex and
absorb the movement between adjoining pieces, but with the continual flexing, these
caulking materials will eventually break down. Without regular maintenance, the
caulked joints will leak. Then, high moisture content of the wood around the joint
leads to loss of wood strength (see Appendix–Wood data, page 75), loss of fastener
holding power, more flexibility and even more moisture penetration.
An often repeated misconception about wooden boats suggests that it is their nature to
be flexible, and that flexibility is desirable because it contributes to the “soft ride” that
makes wooden boats appealing. But, as those who race boats know, a flexible boat
absorbs power. It is harder to push through the water than a stiff boat and for the
reasons stated above it is not as durable. A stiff hull is faster, more efficient, and more
durable in the long run. A soft ride is better achieved with a good hull design. The
flexible approach implies that a wooden boat is at its best just before it falls apart.
1.2.2 Dry rot
Dry rot is another cause of wooden boat damage. It is a natural decay process caused by
the growth of brown rot, a type of fungus that feeds on the cellulose in wood fiber.
Along with severe loss of strength, dry rot causes the wood to discolor, crack across the
grain and shrink.
Dry rot is a misleading term, since wood must be damp for the fungus to exist. In fact,
all of these four conditions must be present for the fungus to survive:
FOOD—an adequate supply of wood fiber
MOISTURE—moisture content of the wood at or near the fiber saturation
point (above 20%)
WARMTH—76° to 86°F (24° to 30°C) is ideal for rot growth (rot can be
active in temperatures as low as 50°F)
The many joints in a wooden boat are potentially ideal environments for dry rot.
Wherever wood contacts wood, air circulation and evaporation will be reduced. If a
leak occurs, the moisture level of the wood at a joint can easily reach the fiber
saturation level and still allow enough oxygen for rot growth. Wood preservatives
attempt to control rot by poisoning the food supply. This approach has had only
limited success and does nothing to address the problem of loss of wood strength due
to high moisture content.
1.3 WEST SYSTEM epoxy for wooden boat repair
The properties of WEST SYSTEM epoxy that make it valuable for new boat
construction also make it ideal for repairing older boats. The techniques in this manual
are designed to take maximum advantage of epoxy’s properties within the limits of an
existing older structure.
WEST SYSTEM epoxy is a structural marine adhesive, formulated to bond to wood.
Epoxy is used in the construction of new wooden boats that are both lightweight and
very rigid. Bonding joints with epoxy provides greater bonding area than mechanical
fasteners and totally seals and protects joints from moisture. Joints bonded with WEST
SYSTEM epoxy are often stronger than the wood being bonded. Bonding with epoxy
requires little clamping pressure, with staples and screws often used to hold the pieces
together until the epoxy cures. As an adhesive, WEST SYSTEM epoxy is ideal for
repairing existing damage and reducing flexing in the structure.
WEST SYSTEM epoxy is unequaled as a moisture barrier.
Epoxy’s ability to protect wood structures from water has made modern wooden boats
nearly immune to dry rot. To a degree, this protection can be applied to older wooden
boats by keeping the moisture content below the point where dry rot can survive.
WEST SYSTEM epoxy has excellent gap-filling qualities.
This eliminates the need for precise fits and a lot of clamping pressure.
WEST SYSTEM epoxy is easy to use and versatile.
WEST SYSTEM products include a complete line of epoxy materials and supplies
developed to meet a wide range of building and maintenance needs. Both amateurs and
professionals can tailor the epoxy system to meet the specific needs of the project.
WEST SYSTEM epoxy and repair information is backed by over thirty years of
Gougeon Brothers, Inc. has been manufacturing WEST SYSTEM epoxy since 1969
and has earned a reputation for excellence in formulating practical, long-lasting and
affordable epoxies for marine construction. New sail and power boats constructed
with WEST SYSTEM products have dominated many classes of competition and
families are cruising throughout the world in seaworthy craft built, restored or
maintained with WEST SYSTEM epoxy. Gougeon Brothers, Inc. has the construction
experience, research and testing, and qualified technical staff to answer specific repair
questions and provide expert guidance to those using WEST SYSTEM products.
1.4 Key steps in repair and restoration
The three key steps in formulating a plan for the use of epoxy in the repair or
restoration of wooden boats are:
Bonding for stiffness
Coating for moisture protection
Ventilating for longevity
1.4.1 Bonding for stiffness
The issue of stiffness is fundamental in our thinking about epoxy in marine structures.
As mentioned, the loss of stiffness in the original structure is one of the problems
leading to the boat’s deterioration. When you use epoxy to repair or restore a boat, you
are introducing stiffness into the structure. If you are planning an overall restoration of
the boat, the comprehensive use of epoxy as the adhesive and moisture coating will
give you a very stiff and durable structure.
What if you are not planning a total rebuild, but are interested in large or small local
repairs to a basically sound boat? Bonding and encapsulating wood with epoxy can
greatly increase the local or the overall stiffness of a boat. Most of the time this stiffness
if beneficial. Occasionally, if the job is not well planned, the newly introduced stiffness
can have a detrimental effect, usually in the form of stress concentration, on the
durability of the repairs or the integrity of the original boat.
First, identify the structural unit that you want to repair and how it fits in the overall
boat structure. Look for structural units where the newly introduced stiffness will not
work against the original structure. Many times this approach can help you set limits to
the repair job. We suggest that you look for the logical breakdowns in the structure.
Scarfing a plank, rebuilding a hatch, replacing the transom, replacing a frame,
rebuilding the top of a deck house, replacing all of the deck—all of these are
possibilities. Edge-bonding the hull planking with epoxy after cleaning the seams is the
single best thing you can do.
1.4.2 Coating for moisture protection
Encapsulating offers a valuable advantage to new wooden boats by forming a
continuous moisture barrier over every part of the boat, inside and out. By coating
every surface of every piece of wood in the boat with at least two coats of epoxy, the
moisture content of each piece remains at a constant level far below the fiber saturation
level and the structure is dimensionally stable. Encapsulating is easy to accomplish
while building a new boat because every piece can be coated at the most convenient
point before or after it is bonded in place. Especially important is being able to coat
pieces or surfaces that can no longer be reached once the structure is assembled.
Encapsulating an older or conventionally built boat is not possible unless all of the
surfaces, especially the contact surfaces of joints, can be coated. This would involve
disassembling the boat, piece by piece, and bonding it back together. You’ll have to
decide if your boat is worth this much effort. However, even if you cannot encapsulate
the entire boat, you can look for structural units that might be encapsulated. You might
be able to encapsulate some areas by removing and bonding one piece at a time
“Can I coat the inside of my boat with epoxy?” is a question often asked. In most cases,
you are better off not coating the interior. Just to coat as many surfaces of the interior
as you can reach leaves many uncoated surfaces and is not the same as encapsulating
since it does not ensure a continuous unbroken moisture barrier and will not eliminate
joint movement or prevent moisture from entering a joint. Failing to coat the
inaccessible contact surfaces of joints can create ideal environments for dry rot if there
is a leak. So keeping the interior well ventilated is often a better solution than
attempting to coat areas that may trap moisture. The object is always to deny at least
one of the four conditions necessary for rot to survive, in this case keeping the wood
moisture content below the saturation point. If you can’t guarantee keeping water out
of the structure, the next best option is to guarantee that it is not trapped in.
What about coating the exterior of the hull? If you eliminate movement between the
hull planks by bonding them together, coating the exterior of the hull is a good idea.
When the framing is sound, edge-bonding the planking, coating the exterior and
ventilating the interior is a good intermediate repair. It adds a lot of stiffness to the
structure, eliminates a source of moisture entering the boat and, when the boat is
properly ventilated, does not trap moisture in the boat.
1.4.3 Ventilating for longevity
Ventilation is the key to the continued longevity of your boat. No boat is
maintenance-free. Either you consider preventive maintenance or you accept periodic
rebuilding and repair. All boats—wood, fiberglass, aluminum and steel—need good
ventilation. Keeping the boat’s interior as dry as possible is the best preventive
maintenance for preserving the structure and making the boat more comfortable.
Clean bilges, an open interior layout, watertight deck openings and effective
ventilators all work together to provide good ventilation. If you have questions about
options, we suggest you consult the books on boatbuilding, outfitting and storing your
boat listed in Appendix–Additional reading, page 77.
Inspecting and Evaluating
2 Inspecting and Evaluating
To evaluate the condition of your boat you need to answer the first two questions listed
in Section 1:
What type of construction is the boat?
What condition is the boat in?
Understanding how your boat was built can help you assess the damage that has
occurred. A knowledge of the structure will make you alert to less obvious damage and
aid you in determining whether the damage has compromised the integrity of the boat.
To assess the condition of your boat you will need to inspect it thoroughly. This
probably will involve some dismantling.
2.1 Understanding the Structure
Evaluating the soundness of your boat involves recognizing how well the individual
and combined structural components are still doing their job. Most wooden boats are
characterized by a structural framework covered with a protective skin.
2.1.1 The structural framework
While they may vary in size, shape and function, most wooden boats have common
structural elements (Figure 2-1). The elements form the overall framework and work
together with the planking to carry loads. The heavier framework of conventionally
planked boats is designed to provide most of the structure’s stiffness. During the
building, after the boat is launched or when she is hauled for service, the various
structural members carry and distribute the concentrated and heavy loads of the boat.
More contemporary boats with plywood skins may have less or lighter framework.
Look at each of the elements of your boat’s structure to see whether it still has the
strength to carry the load it was designed to carry.
The keel is the backbone of most boats. Traditionally the heaviest, most rigid element
in the structure, it provides a foundation for the rest of the structure. Like all
components, the keel should not only be strong enough to resist bending but also solid
enough to hold the fasteners that transfer loads from adjoining parts.
Frames and floor timbers run athwartships at regular intervals along the keel. The
symmetrical frames give the hull shape while the floors distribute the loads from the
ballast keel or engine stringers out over even more of the planking.
Inspecting and Evaluating
Figure 2-1 Typical structural framework.
Deck beams connect the tops of each pair of hull frames. Collectively they tie the two
halves of the hull together, preventing the hull from spreading or collapsing and
supporting the deck skin. The end of each beam rests on and is connected to the sheer
clamp and is usually connected to a frame end as well.
The sheer clamp is connected to both the beams and the frame ends. It ties all the frame
ends and beams together along the top of each side of the hull (the sheer) from stem to
On larger boats a shelf, attached to the sheer clamp on the flat, helps to support the
beams and stiffen the sheer. The clamp sits vertically against the frame ends and the
shelf lies horizontally under the end of the beam. The shelf and sheer clamp are
connected at approximately right angles.
Some round bottom boats may have intermediate bilge stringers providing additional
stiffness along the turn of the bilge. These stringers, running fore-and-aft, are located
halfway between the keel and the sheer clamp. On flat-bottom, multi-chine, or
v-bottom boats, the intermediate fore and aft stringers are called chines or chine-logs.
These structural members can be quite light in certain types of construction but can be
very heavy, equaling the size of keel or clamp, in some traditional boats.
On powerboats and large sailboats the engine beds or stringers can be very large.
Typically they will run some distance fore-and-aft of the engine and be tied into the
floors of special bulkheads.
On some larger boats there will be knees or strapping installed beneath the planking
and decking to resist diagonal or torsional movement. These additional reinforcing
members can be wood or metal.
At cockpit or cabin openings a carlin ties the ends of the short or half beams to a full
beam at each end of the opening. Extra knees and tie rods help to stiffen the sheer and
transfer the load to the next full length beam. In a small open boat the sheer must be
stiff enough to resist flexing without the aid of deck beams. In a canoe, for example,
one or two thwarts replace a deck and the sheer must be stiff enough to resist flexing
between the thwarts.
Inspecting and Evaluating
2.1.2 The skin
One of two basic types of skins covers the hull and deck structure, providing a
watertight membrane. Variations of planking provided the only alternatives for
covering wooden structures for thousands of years until modern adhesives made the
plywood skin more common and more durable.
Planking, whether carvel or lapstrake or a variation of these, is more susceptible to
flexing and leaks than plywood. The individual planks run generally parallel to the
centerline of the boat (Figure 2-2). They rely on fasteners at each framing member and
the caulking to resist shear movement (the slight sliding movement between planks
when a hull twists). In lapstrake planking, where each plank overlaps the preceding
one, clinch fasteners or screws along the lap serve to tighten the lap and resist shear
along the lap. Joints between carvel planks were traditionally sealed with cotton and/or
oakum caulking driven into the seams with a caulking iron and filled over with tar or
flexible sealant. Driving the caulking into the seams helped to stiffen the boat initially,
but caulking needed to be redone as the boat’s fasteners worked and the planking
swelled or shrank.
Double planking was usually two layers of carvel, or square seam planking, sealed
between seams and layers with shellac, paint, bedding compounds or glue.
Occasionally canvas, bedded in paint or white lead, would be used between the
planking layers.
Figure 2-2 Typical laid plank deck and carvel planked hull.
Figure 2-3 Typical plywood construction.
Plywood often replaces the many individual planks, greatly reducing the number of
joints that are potential sources for leaks. The framework for a plywood skin is similar
to the framework for planking. But, because the plywood is strong in more than one
direction, the framework for plywood covered structures can be much lighter. The
extra frames required in a planked structure to resist diagonal movement can be
eliminated. The plywood sheets are usually glued to the framework and held in place
with staples, nails or wood screws (Figure 2-3). Multiple layers of thinner plywood are
used on surfaces with compound curves where a single thick layer can’t bend enough in
both directions.
Plywood can also suffer from moisture problems. Moisture can penetrate plywood
through the end grain at seams, causing delamination. On the surface, moisture causes
the top veneer to check. Early plywood decks were protected with canvas laid in a fresh
coat of paint or canvas cement. The fabric may have offered some protection, but
Inspecting and Evaluating
because moisture can be trapped under a large area of the fabric, serious damage can be
done before it’s discovered. When you notice the soft deck or the loose fabric, the
plywood may have already lost much of its strength.
Besides the problems of joints in the deck itself, deck hardware is a major source of
deck leaks and moisture damage. All deck hardware is anchored to the deck with
mechanical fasteners that penetrate the skin. Lightly loaded hardware may be simply
screwed into the skin. Hardware items that take high loads need to be screwed or
bolted through the skin into a structural member (e.g., a deck beam or extra blocking)
that can transfer the load over a larger area. If all the mounting holes are not drilled
precisely, the fasteners holding the hardware in place will not share the load equally.
The hole with the most highly loaded fastener elongates as the hardware is stressed
repeatedly. Movement reduces the load-carrying capacity of the wood fiber
surrounding the fastener and creates an entry point for water. Bedding compounds,
designed to seal out moisture between the hardware base and the deck surface, do
nothing to prevent movement of the hardware. Over time, this movement will break
down the bedding material and eventually allow moisture into the fastener hole.
Moisture can quickly penetrate the end grain of the hole, weakening the fastener’s grip
even further.
This overview of a boat’s structure highlights some of the problems you are likely to
face as a wooden boat owner. While these problems may be daunting, they don’t have
to be fatal. One of the beauties of wood is its resilience. With a little resuscitation and
the proper protection, your boat can begin a long and low maintenance second life.
If you would like a more thorough discussion of boat structure, consult the books listed
in Appendix–Additional reading, page 77.
2.2 Inspecting and locating damaged areas
The first phase of repair involves inspecting and locating damaged areas. Even though
damage may be obvious, finding all the hidden damage will probably require some
dismantling. Because hidden damage from trapped moisture is a major problem with
wooden boats, a thorough job of dismantling is important. A careful inspection will
allow you to make better decisions about what repair procedures to follow as well as let
you know just how big a job you are in for.
Figure 2-4 Look for dry rot at joints and areas of standing water and poor air
Inspecting and Evaluating
Begin your inspection as follows:
1. Support the boat in its proper shape. Stem and transom centerlines should be plumb.
The sheers should be level at each station. Brace or shim the hull to prevent any
movement before the repair is complete. The more parts that are bonded with epoxy,
the more rigid the final structure will be. When the repairs are complete, the boat will
retain the shape in which it was supported.
2. Remove equipment, hardware and accessories, canvas covering, trim and fiberglass
cloth if it is loose.
3. Find the sources of leaks and the areas affected by leaks before the boat dries out. Look
for damp areas, peeling paint, soft or discolored wood. Remove the old finish as
necessary to judge the condition of the wood underneath.
4. Inspect each structural member and its fasteners to see if they can still carry their
intended load. Use an ice pick or other sharp tool to probe for areas of dry rot. Look for
rot in areas of poor air circulation, where parts contact each other and around
fasteners. If the damage is from an impact or fatigue, look for cracked frames or loose
fasteners away from the obviously damaged area (Figure 2-4).
5. Remove damaged material and parts that block access to suspected damage. As
necessary, dismantle the skin and underlying structure in reverse order of construction
until all of the damage is removed or accessible. Carefully remove and save salvageable
parts for reassembly. Some parts, although damaged beyond repair, may still serve as
patterns for fashioning a replacement. Removing the damage does not necessarily
mean removing the entire part. Often a part can be repaired in place by scarfing in a
new section or adding reinforcing (see Section 4.3).
6. Dry the boat thoroughly before beginning repairs. Remove all the remaining old finish
and provide plenty of ventilation to speed the drying process. The wood moisture
content should equilibrate at 8%–12%. The structure will then be dimensionally
stable, the epoxy will bond better and the moisture won’t be sealed in. Provide a dry,
sheltered work area for the boat and yourself.
Reassess the project
Once you’ve completed your inspection, you’ll know exactly what condition your boat
is in and will be better able to plan your repair. We urge you to again consider the
questions posed in Section 1:
What results are you looking for? A quick repair, a complete restoration or
something in between?
Are you prepared to commit the time and resources to get the results you’re
looking for?
Is wood/epoxy construction the best solution to your problem?
When you are clear on your answers to these questions, you are ready to proceed on
your repair or restoration and use the following sections of this manual as appropriate.
Section 8 provides fundamental techniques for using WEST SYSTEM epoxy products
successfully in wooden boat repairs. Even if you are familiar with these products, it is
important to make sure you thoroughly understand the basic techniques for surface
preparation, bonding, bonding with fillets, laminating, fairing, and applying woven
cloth and tape which are discussed in Section 8. Sections 3–7 of the manual provide
detailed procedures for particular types of repair and can be used in whatever order
your repair requires.
Repairing Localized Dry Rot
3 Repairing Localized Dry Rot
Repairing small areas of dry rot may be the most common repair to wooden boats.
Most structures have many small, isolated areas with poor ventilation that can trap
moisture and harbor dry rot. These pockets of dry rot often can be repaired in place by
excavating the damage and filling the cavity.
3.1 Excavate and fill
Remove all wood noticeably damaged by rot, making sure to extend well away on both
sides of the apparent damage. Use a chisel to excavate all of the weak, crumbly wood,
leaving a clean cavity with solid wood exposed on all sides (Figure 3-1). Use a wire
brush to remove any remaining soft wood around the cavity. The size of the exposed
cavity will determine which of two filling methods is the most appropriate. You can fill
small cavities with solid thickened epoxy and fill larger cavities by bonding in a
dutchman (wood shaped to fill the cavity).
Figure 3-1 Use a chisel to excavate a cavity that extends beyond all of
the damaged wood.
The decision to fill the cavity with solid epoxy or with wood is based on convenience,
practicality and economics. You can save a lot of time if you can avoid carving intricate
pieces of wood to fit hard to reach areas, but a solid epoxy patch weighs more and costs
more per pound than wood. Also, you are limited by the epoxy’s exothermic reaction
to about a 1 2" layer (using 205 hardener) in one application. A larger volume would
heat up enough to cause foaming and significant weakening of the epoxy. Although
you may use slower hardener and/or apply the epoxy in multiple layers to avoid
exotherm, there are practical limits to the size of cavity that can be filled with solid
Repairing Localized Dry Rot
3.1.1 Filling with epoxy
Small cavities are most conveniently filled with solid thickened epoxy as follows:
1. Prepare the surface (Section 8.4.1). Be sure the area is thoroughly dry.
2. Wet out the repair area with the resin/hardener mixture (see Two-step bonding, page
3. Fill the cavity with epoxy thickened with a high-density (406,404 or 403) filler to a
peanut butter consistency. Trowel the mixture into the void with a plastic spreader or
mixing stick (Figure 3-2). Smooth the mixture flush with the surface and remove any
excess before the mixture begins to cure.
4. Allow the mixture to cure thoroughly before sanding.
Figure 3-2 Trowel thickened epoxy into smaller voids.
Figure 3-3 Bond a dutchman into larger cavities. Bevel the sides
of the cavity and the dutchman to match.
3.1.2 Filling with wood
§ Dutchman—A
small piece of wood
shaped to closely fill the
void in a larger piece of
Larger cavities should be filled with wood wherever possible. This method restores the
original strength of the wood. The procedure involves carving a dutchman to the shape
of the void and bonding it in place with epoxy as follows:
1. Prepare the dutchman. Use the same kind of wood if possible. Carve the cavity to a
geometric shape if necessary to make shaping the plug easier. Bevel the sides of the
cavity. The longer the bevel on the sides running across the grain, the stronger the
repair (Figure 3-3). An 8-to-1 bevel (8" long for every 1" deep) or greater will be close to
the original strength of the wood. Check the dutchman for fit. Thickened epoxy will
fill a fairly large gap, so the fit doesn’t have to be perfect. Prepare the surfaces for
bonding (Section 8.4.1).
2. Wet out the bonding surfaces of the cavity and the plug with resin/hardener mixture.
3. Apply thickened epoxy/adhesive filler (406, 404 or 403) (mayonnaise consistency) to
the cavity surfaces. Using the mixing stick, apply enough of the thickened mixture to
fill any gaps.
4. Insert the plug into position. Thickened epoxy should squeeze out of the joint.
5. Clamp the plug into position. Weights or staples may be used to hold the plug until the
epoxy cures. Remove excess epoxy before it begins to cure.
6. Allow to cure thoroughly before removing clamps or sanding.
Repairing Localized Dry Rot
3.2 Drilling and filling
A common, but much less effective, method of dealing with rotted areas is to drill a
pattern of holes in the affected area and inject epoxy into the holes to penetrate and
stabilize the area. This is a last resort method, especially if wood strength is critical. The
biggest problem with this method is that you can never be sure of the extent of epoxy
penetration into the damaged wood. Testing of the physical properties of repaired
samples shows drilling and filling to be inferior to excavating and filling. Also, drilling
and filling is impossible on overhead surfaces and difficult on vertical surfaces.
However, it may be useful in some situations, where maximum strength is not required
or the rotted area is too difficult to reach for excavating and filling. If you choose this
method, we recommend the following procedure:
1. Drill a pattern of 316" diameter holes over the rotted area. Space the holes 1" or less
from center to center in all directions. Drill each hole deep enough to pass through the
rot, just into solid wood. On vertical surfaces, drill the holes downward at
approximately 45°.
2. Dry the area thoroughly. If necessary, use heat guns or fans to accelerate drying.
3. Inject or pour resin/hardener mixture into the holes. Epoxy penetration can be
improved by first warming the wood with a heat gun. On contact with the warmed
wood, epoxy will become thinner and penetrate more deeply into the exposed end
grain. A mixture using 206 Slow Hardener should penetrate more deeply than 205
hardener before it begins to gel (Figure 3-4).
Figure 3-4 Inject resin/hardener mixture into holes until the
damaged wood absorbs all it can.
Figure 3-5 Fill the remaining voids with fairing compound.
4. Continue to add epoxy to the holes until the wood is saturated and can no longer
absorb more.
5. Fill remaining voids with thickened epoxy after the epoxy reaches its initial cure, if
desired(Figure 3-5). Use an epoxy/fairing filler mixture for cosmetic fairing of the
surface (see Section 8.4.4).
Repairing Localized Dry Rot
3.2.1 Thinning epoxy
There are epoxy-based products specifically designed to penetrate and reinforce rotted
wood. These products, basically an epoxy thinned with solvents, do a good job of
penetrating wood. But the solvents compromise the strength and moisture barrier
properties of the epoxy. We are often asked if WEST SYSTEM epoxy can be thinned
with solvents for greater penetration. The answer is yes, but not without the same
compromise in strength and moisture resistance. Laquer thinner, Acetone, and
denatured alcohol have been used to thin WEST SYSTEM epoxy, duplicating these
penetrating epoxies with about the same effectiveness.
If you chose to thin the epoxy, keep in mind that the strength and moisture protection
of the epoxy are lost in proportion to the amount of solvent added. Adding 5% laquer
thinner results in a 60% reduction in viscosity. It also reduces epoxy’s compressive
strength by 35%.
There is a better solution to get good penetration without losing strength or moisture
resistance. We recommend moderate heating of the repair area with a heat gun or heat
lamp (to about 115°F—still comfortable to touch). The epoxy will have a lower
viscosity and penetrate more deeply when it is warmed by contact with the warmed
wood cavities and pores. In addition, heat will expand air in the wood pores causing it
to out-gas. When the heat is the removed, the cooling wood will draw epoxy back in.
Slower hardeners (206, 207, 209) will have a longer working life and should penetrate
more than 205 Hardener before they begin to gel. When the epoxy cures it will retain
all of its strength and effectiveness as a moisture barrier, which we feel more than
offsets any advantages gained by adding solvents to the epoxy.
3.3 Reinforcing
Tensile strength can be added to a dry rot repair area by using synthetic fiber such as
fiberglass, carbon fiber or Kevlar® in appropriate amounts with epoxy. Refer to
Section 8.4.5 for application information. Apply the reinforcing after the dry rot has
been excavated and filled, or drilled and filled.
Stainless steel threaded rod has also been used to reinforce and join pieces with
excellent results. The rod can be bonded into drilled or grooved pieces as a structural
pin to tie individual or separate pieces together. See Section 6.4 for information on
bonding threaded rod.
Repairing the Structural Framework
4 Repairing the Structural
Replace or reinforce in place framework that is too weak to carry its designed load.
Structural framework includes the keel, stems, hull frames, stringers, deck beams,
sheer clamps, shelves, knees, carlins or thwarts. They vary widely in size, shape and
position, but have many problems and repair techniques in common.
Frames can be damaged from dry rot or from impact. Under impact, frames often
break in multiples. If you find a cracked frame, take the time to look for others,
especially adjacent to the broken one. Hull frames often break at stringer edges, the
turn of the bilge and at the reverse turn (especially in the stern). Examine the outside of
the hull for a knuckle or unfair spot in the planking in the area where the frames are
damaged. If you find planks that are out of position, temporarily force the affected
planks (and frames) back using whatever means are available. You may use bracing and
shims on the outside of the hull and/or rope and tackle on the inside. The frame repair
can begin once the shape of the hull is restored.
Frame repairs rely on replacing damaged frames or sections of frames with material
that is of equal or greater strength (see Appendix–Wood data, page 75). Laminating is
an efficient method of building frames and a basic technique for the frame repairs in
this Section.
4.1 Laminating beams, frames and stems
Frames can be cut from solid stock or steam bent if you plan to restore the structure
exactly. (If you steam bend frames, be sure to allow plenty of time for the frame to dry
out before bonding.) However, laminated frames have many advantages over steam
bent frames, both structurally and in ease of fabrication. Whole and partial frames are
made of multiple thin layers of wood to duplicate the shape and dimension of the
damaged frame (Sections 4.2, 4.3 and 4.4). There are no limitations to the size of frame
that can be laminated. Laminating may be the only practical or economical way to
duplicate large structural members as large timber becomes more scarce. The new
frame can be laminated in a simple jig made from a pattern or, in some cases, directly in
place in the hull.
Keep in mind the following when selecting wood for laminating frames:
1. Choose wood strips that are the same or similar species as the original frame.
2. Use wood strips thin enough to bend easily into the shape of the original frame. Be sure
all of the strips collectively can bend to shape. When fewer, thicker strips are used for a
given thickness of frame, more stress is induced resulting in less strength and more
Repairing the Structural Framework
springback in the curved frame. Using more, thinner strips results in a curved frame
with greater strength and less springback, but requires more labor and epoxy to build.
Use thinner strips especially with harder woods like white oak.
3. Use full-length strips. Make the strips longer than the finished frame to allow for
4. The new frame width should be the same as the original frame. Strips can be wider to
allow for trimming and finishing after the frame is laid up.
5. Select wood strips that are seasoned. Ideal moisture content is 6% to 14%.
4.1.1 Laminating in a jig
A laminating jig will allow you to laminate a new frame in the controlled environment
of your shop. Use cardboard or other convenient material to pattern the top or bottom
line of the damaged frame. Transfer the pattern line to a laminating jig of one the types
illustrated (Figure 4-1).
Laminate frames in a jig as follows:
1. Prepare the jig and the strips as suggested. Go through a dry run to be sure the strips
bend enough and that your jig and clamps can handle the bending of all of the strips.
Cover the jig with plastic to prevent the frame from bonding to the jig.
2. Wet out the strips on both sides with epoxy, except for the outer faces of the top and
bottom strip.
Figure 4-1 Transfer the desired frame shape to the jig.
3. Apply thickened epoxy to one side of each strip and stack it in place on the jig against
the previously coated strip. Thicken the mixture with 406 filler to a catsup consistency.
Be sure one side coated with thickened epoxy faces each joint.
4. Clamp the strips to the jig until the epoxy cures (Figure 4-2). Use clamps, wedges,
staples or small nails to apply enough pressure to squeeze a small amount of epoxy
from each joint.
Repairing the Structural Framework
Figure 4-2 Clamp the appropriate number of coated strips into the jig. Trim the
frame to size after the epoxy is fully cured.
5. Remove the frame from the jig after the epoxy has thoroughly cured. Be sure to allow
extra cure time if the temperature is cool, especially if you expect a lot of springback.
Trim the frame to its final shape and finish as desired.
4.1.2 Laminating frames in place
The new frame or frame section can, in some cases, be laminated directly in place in the
hull. The existing structure can be used as the laminating jig in one of the following
A) Bond all of the strips permanently to the structure in one continuous operation, either
one at a time or all at the same time, depending on the best available clamping method.
Use non-corroding screws or staples to bond strips in place one at a time, if temporary
clamping is not feasible. Try a dry run to see which method will work best. Trim all of
the strips to size before bonding.
B) Bond all of the strips together in place with plastic over the hull contact area to prevent
immediate bonding to the hull. Remove the laid up frame and trim to size. Bond the
new frame back into place permanently, as previously described.
4.2 Removal and replacement of frames
Often a framing member is too damaged to be repaired and replacement is the best
option. Replace a damaged frame as follows:
1. Support the hull and remaining structure before removing frames. If necessary, leave
some damaged frames to maintain the shape, replacing them after new frames are
installed. Remove all fasteners holding the frame. Cut the damaged frames into
sections, if necessary, to remove them.
2. Laminate the replacement frame using the instructions in Section 4.1.1. You may also
cut or steam bend a frame to match the original if you choose. Trim the frame to fit.
3. Prepare the frame and contact area for bonding. Avoid bonding to anything you intend
to remove later.
4. Install the frame. Wet out all contact areas with epoxy. Apply a thickened epoxy/406
mixture to one side of each contact area.
Repairing the Structural Framework
Figure 4-3 Install the new frame in the same position as the
old frame. Braces or screws may be used to hold the frame until
the epoxy cures.
5. Clamp the frame in position until the epoxy cures. If the fasteners of the old frame are
to be reused, bond the fasteners with epoxy.
4.3 Removing and replacing a damaged section
Often damage to a frame is limited to a small section or the frame may be too difficult
to remove. You may be able to replace only the damaged portion, restoring the
strength of the frame while leaving the frame in position in the boat.
1. Cut out the damaged section of the existing frame. Trim the exposed ends to a
minimum 8-to-1 scarf angle (Figure 4-4). The longer the scarf angle, the stronger the
joint. When repairing hardwood or highly loaded frames, use a longer (12-to-1) scarf
Silicon Bronze fasteners
if permanently left in
Figure 4-4 Cut out all of the damaged area, leaving at
least an 8-to-1 bevel on the ends of the damaged frame.
Figure 4-5 Bond in a new laminated or solid section trimmed to
fill the void in the existing frame.
Repairing the Structural Framework
2. Laminate a new piece slightly larger than the removed section, or carve a new section
out of solid wood, using the same wood as the existing frame. Trim the new section to
fit the size and shape of the void in the existing frame. Cut a matching scarf angle on
each end of the frame section.
3. Prepare the surfaces for bonding. Trim the new piece and existing frame ends as
necessary for a good fit.
4. Install the new frame section (Figure 4-5). Wet out all contact surfaces of the new and
existing frame ends. Apply a liberal amount of thickened epoxy/406 mixture to one
side of each contact area.
5. Clamp the section in position. Clean up excess epoxy before it cures. Remove clamps
after epoxy cures thoroughly.
4.4 Installing sister frames or doublers
Sister frames are bonded alongside a damaged frame to restore the strength of the
original frame. This method may not look as good as a replaced frame but it will save
time, especially if the damaged frame is difficult to remove. Install sister frames as
1. Laminate a full sister frame slightly longer than the existing frame and trim it to fit tight
against the damaged frame. Laminate a partial sister frame so that it will extend past
each end of the damaged area twelve times the thickness of the frame (Frame 4-6). A
sister frame may also be carved out of solid wood. Use the same wood as the existing
Figure 4-6 Laminate a partial sister frame longer than the damaged area.
2. Prepare the contact areas of both frames and the skin for bonding. Avoid bonding to
the planking or plywood if it will later be removed.
3. Install the new frame section. Wet out all contact surfaces of the new and existing
frames. Apply a liberal amount of thickened epoxy/406 mixture to one side of each
contact area.
4. Clamp the section in position. Clean up excess epoxy before it begins to cure. Remove
clamps after epoxy cures thoroughly.
Repairing the Structural Framework
4.5 Joint repairs
If the framing is not damaged from rot or impact, you may still want to bond the
framing together to stiffen the structure and seal the joints against moisture. Remove as
many frames as you can and bond them in place using the standard bonding techniques
in Section 8.4.2. Many of the frames that can’t be removed can still be bonded into
place as follows:
1. Support the boat in its proper shape before bonding any joints.
2. Open as many of the joints as you can reach, between frames and between frames and
the outer skin. Loosen fasteners wherever possible. A small pry bar or wedge may be
used to force the joint open temporarily. Use a saw blade or other sharp tool to scrape
out old paint, varnish or dirt from the joints (Figure 4-7). Clean the inner joint surfaces
to bare wood as much as possible.
Figure 4-7 Use a scraping tool to clean out and abrade the inner
joint surfaces.
Figured 4-8 Inject epoxy as far as possible into the joint.
3. Wet out the inner contact areas of the joint. Use a syringe, small brush or pipe cleaner
to reach the middle of the joint.
4. Apply thickened epoxy to the contact area of the joint. Use a syringe to inject an
epoxy/406 filler mixture to the middle of the joint (Figure 4-8). A small plastic tube or
straw taped to the spout of the syringe will extend the reach of the syringe into a tight
area. Inject enough of the thickened mixture so that a small amount will squeeze out
when the joint is clamped together.
5. Clamp pieces in position until the epoxy cures. Tighten fasteners to draw the joint
closed. Fasteners may be bonded in place for moisture protection and added strength
(see Section 6).
4.6 Repairing garboards
The garboard is the plank which meets the keel or deadwood. It sometimes separates
from the keel, allowing water to leak into the boat. If this leak recurs season after
season even after the seams are thoroughly caulked, you may have a serious problem to
Repairing the Structural Framework
attend to. The wood keel may be pulling away from the floors (the wood timbers that
tie the frames into the keel) or the floors may no longer be tied effectively to the frames.
To check for this:
A. Inspect the area where the floors attach to the frames. Look for signs of movement
between the floors and the frames (Figure 4-9).
B. Inspect the area where the floors attach to the keel. Look for a gap between the floors
and keel.
Figure 4-9 Inspect the floors, keel and frames for gaps or signs of
4.6.1 Repairing floors
If gaps exist between the frame and floors or the floors and the keel, they will cause the
garboard seam to open. The following repair procedures will correct the problem and
permanently attach the floors to the frames and keel:
1. Remove the garboards and one or two additional planks from each side of the hull.
2. Prepare the keel, floors, and frames. Remove old paint or varnish and sand to bare
wood. Dry the area thoroughly.
3. Cut new floors to fit opposite the old floors on the opposite side of the frames. They
may be laminated or cut from solid stock.
4. Cut filler blocks that fit between the frames and between the new and old floors.
5. Bond the new floors and blocking to the keel and frames (Figure 4-10). Wet out all
mating surfaces and end grain with resin/hardener mixture. Apply thickened
epoxy/406 filler. Clamp in position until epoxy cures. Allow the epoxy to cure
thoroughly before removing clamps and proceeding with the next step.
6. Drill two vertical holes at each hull frame, through the blocking and at least 3" into the
keel. The diameter of the holes should be 1 8" larger than the threaded rods selected for
this repair.
7. Cut a piece of stainless or hot dipped galvanized threaded rod to match the depth of
each hole. The threaded rod should be the same diameter as the original keel bolts.
8. Wet out one or two holes at a time with unthickened resin/hardener mixture. Allow the
epoxy to penetrate the end grain inside the hole.
Repairing the Structural Framework
Figure 4-10 Bond new floors and blocking to the keels and
Figure 4-11 Bond threaded rod through the blocking and at least
3" into the keel.
9. Fill the wet-out holes half full of thickened epoxy/404 or 406 filler. Apply thickened
epoxy to the threaded rod, filling the threads.
10. Push the coated rod to the bottom of the filled hole (Figure 4-11). Fill the holes to the
top as necessary. Clean up excess epoxy before it cures.
4.6.2 Reinstalling garboards
The keel, floors and frames are now permanently tied together with epoxy and
threaded rods. With this completed, bond the planking removed earlier to the keel and
1. Prepare the planking and frames for bonding. Remove all old paint or varnish. Sand
the areas to be bonded to expose new wood fiber.
2. Dry fit the planks to the hull. Drill new holes for screws if the old ones don’t align. Be
sure you have enough clamps to draw the planks to the frames.
Figure 4-12 Bond the garboard back into position next to the keel.
Repairing the Structural Framework
3. Wet out the screw holes (new and old) in the planks, frames and keel with
resin/hardener mixture, using a pipe cleaner or syringe. Wet out the edges and inside
surface of the plank and the bonding areas of the keel and frames with resin/hardener
4. Apply liberal amounts of thickened epoxy/406 filler to the mating surfaces of the keel
and frames.
5. Install the garboard with the original screws (Figure 4-12). Start at the middle and work
toward both ends.
6. Form a fillet along the keel/garboard joint with the excess epoxy and form a fillet
where the planking meets the frames.
7. Follow the same procedure and install the garboard on the opposite side of the keel.
8. Bond the remaining planks together, following procedures discussed in Section 5.
4.7 Keel repair
A keel is a major structural component and should get extra care and special
investigation. Skegs, deadwood or fin keels can pose special problems. Deadwood can
be inside or outside the planking line and typically has a fair number of exposed seams.
It is generally not wise to encase the skeg or deadwood in a fiberglass/epoxy skin unless
you have stabilized the joints in the structure.
Worm damage may require replacement of the specific pieces.
If work is needed on the garboards, floors or frame heels, it is a good idea to examine
the keel while the garboards are off. The joints and rabbets are prime locations for rot
to start. These joints between the pieces of the deadwood or skegs are notorious places
for leaks. The keel bolts or drifts passing from the ballast keel up through the
deadwood, keel and floors allow water to pass up and into the hull.
Follow these procedures to repair the keel:
1. Remove the paint or any other coatings or coverings and allow the hull to dry out
thoroughly (possibly schedule this work for the spring after the boat has had the winter
to dry out).
2. When the seams are open or the keel or deadwood timbers have shrunken, clean out
any old paint, caulking or debris. Make sure that the wood in the joints is dry.
3. Work epoxy thickened with 406 filler into the joints with a plastic spreader from one
side until the epoxy comes out the other side. Clean up excess epoxy from the surface
and allow the epoxy to cure.
4. Either coat the exterior of the skeg or deadwood with epoxy or cover it with a
fiberglass/epoxy skin.
4.7.1 Keel bolt repair
If there has been leaking around the keel bolts, floor bolts, rudder tube or propeller
shaft, follow these procedures:
1. Support and secure the boat and ballast keel.
2. Fabricate a deep engagement hole saw by first cutting the end off a hole saw of slightly
larger diameter than the bolt to be repaired. Braze the hole saw teeth to the end of a
pipe of the same diameter and long enough to chase the length of your longest keel
bolt. Weld a piece of round stock into the other end of the pipe to serve as a bit for a
drill chuck. If you have many bolts of many lengths to do, you may want to make
several hole saws of different lengths (Figure 4-13).
Repairing the Structural Framework
Figure 4-13 A custom keel bolt saw can be made from a pipe
section and a standard hole saw.
Figure 4-14 Build an epoxy reservoir around each keel bolt.
3. After removing the nuts, washers or clinch rings, use the hole saw to chase down along
the bolt. The typical hole saw will produce a clean 0.125" annulus around the bolt. Be
sure the wood is completely dry.
4. After blowing out the dust and shavings, wrap duct tape around the bolt threads and
construct a ¼" high dam around the bolt hole with plasticine (modeling clay) (Figure
5. Overfill the hole with epoxy. Keep the plasticine dam full as the epoxy soaks into the
end grain in the hole.
6. After the epoxy has cured, sand the surface smooth, remove the protective tape and
replace the washers and nuts.
7. Call Gougeon Brothers, Inc. for more specific discussion of repairing larger keels.
Repairing Hull and Deck Planking
5 Repairing Hull and Deck
This section is a guide for the repair of the outer skin of wooden boats. The skin
covering the deck and hull framework of wooden boats can generally be divided into
two categories: planking and plywood. Planking is the older, traditional method of
covering hulls and decks and is more susceptible to flexing and leaks than plywood.
Modern adhesives have made plywood a more common and practical skin for wooden
structures. The procedures in this section deal with the problems and repairs for the
most common types of skins. Select the procedure or combination of procedures that
best fits your situation.
5.1 Carvel planked hulls and laid plank decks
For centuries, carvel planking and laid plank decking were the only methods of
enclosing a boat. Carvel planking and laid plank decking are essentially the same
method, in which many individual boards are laid edge to edge, fastened to each frame
and caulked. Eventually the structure loosens up, the caulking breaks down and the
planking becomes a constant source for leaks and endless maintenance. While carvel
hull planking and laid plank decks vary in the size and placement of the planks, they are
similar in function and can be repaired with the same techniques.
As mentioned in Section 1.4.2, the ideal reconstruction would be to remove the
planking, clean and strip it of paint, and bond it edge to edge and to the framing timbers.
If you can do this, you can eliminate places where moisture can become trapped and
could then coat both the inside and the outside of the hull with epoxy to encapsulate it.
Remember, you can only encapsulate the boat with epoxy if all of the surfaces, especially
the contact surfaces of joints, can be coated.
If, however, the framing is sound and you don’t want to remove the planks, your best
solution to leaks and loss of stiffness is to (1) clean out the seams, (2) bond the planks
together with epoxy and (3) coat the exterior with epoxy and (4) ventilate the interior
to reduce expansion and contraction. This seals the seams permanently and eliminates
movement between planks. A strong bond between all the planks will result in a much
more rigid structure.
IMPORTANT! As a rule, edge bond the planks only if you coat the exterior—coat the
exterior only if you edge bond the planks.
Edge-bonding the planking and coating the exterior will stiffen the structure and
reduce maintenance. Below the waterline it will also stop water penetration through
the hull, help keep the interior drier and dry wood is stronger than wet wood. It will
allow the boat to be dry sailed, no longer relying on the planks to swell before it is
water tight. In many cases it is advisable to make this repair below the water line only.
Often it is the first stage in a restoration or it may be the only improvement to an
otherwise sound boat.
Repairing Hull and Deck Planking
5.1.1 Cleaning out the seams
Getting a good clean bonding surface on each plank edge is the first step. You can use a
circular saw, a router, a chisel and hammer, or a sharpened scraper to clean all the old
caulking material out of the joint and expose clean fresh wood for bonding on the
facing edge of each plank. One tool may work better than another in a given situation,
but a circular saw is usually the most effective way to mill out the seam accurately.
1. Dry the hull thoroughly before beginning. This allows the seams to open to their widest
and stabilizes the size and shape of all the pieces.
2. Tack a batten to the hull to act as a guide for the saw. The batten should be parallel to
the seam so the blade will follow the center of each seam exactly.
3. Select a blade or reset the blade’s teeth wide enough to shave the edges of both planks
facing the seam. Use a pair of pliers to bend the teeth for more set. The seam width may
vary, but the cut should be at least 316". If the seams have opened very wide after drying,
two passes with the saw may be necessary to shave both planks.
4. Set the depth of the cut to 116" less than the thickness of the plank. Leave just enough
material at the back of the seam to prevent epoxy from passing through to the inside.
Figure 5-1 Use a circular saw to clean out plank seams.
Figure 5-2 Cut a bevel on the end of each plank.
5. Clean out each seam by running the saw along the batten (Figure 5-1). Check the depth
and width of the cut. Clean out the butt joints at the ends of the plank as well. Chisel a
shallow bevel on the end of the planks (¼" deep x ½" back from the edge) (Figure 5-2).
The bevel increases bonding area and reduces stress at the joint.
A router with a straight fluted bit also will work to clean out seams. Select a bit wide
enough to shave both planks. The router will get into tighter places than the circular
saw, but the bits dull quickly, often break and are expensive to replace.
A chisel can be used in tight spots to carve a “V” groove where a saw or router will not
work. A scraping or “reefing” tool for cleaning out seams can be made from a mill file
as shown in Appendix C or you may invent your own tool or method for cleaning the
seams. Remember, the object is to clean out the old caulk and expose clean wood on
the facing edge of each plank for good bonding.
Repairing Hull and Deck Planking
5.1.2 Filling the seams with wood
After machining a clean gap between two planks, bond a spline of suitable wood into
the gap. The spline should be of the same species or stronger than the planking.
Remember! Support the hull in its proper shape before bonding. The shape of the hull
will be permanently set once the planks are bonded.
1. Prepare the splines. Cut them from stock that is the same species and thickness as the
planking. Rip the splines on a table saw, with the blade set at a 5° angle. Flip the stock
end for end after each pass so each spline will have a 10° taper in cross section. Set the
width of the cut so that the wide end of the taper is the same width as the seam gap. It
should fit snugly when pushed into the gap, just as the narrow end hits the bottom of
the gap. The splines can be any convenient length for easy handling. Cut a 45° scarf on
the ends of each spline.
Figure 5-5 Inject epoxy into the wet-out seam.
2. Wet out an equal length of opened seams and splines with resin/hardener mixture. Use
a glue brush or swab to wet out the seam. Use a foam roller, cut to a narrow width, to
wet out the splines.
3. Apply a bead of epoxy/403 or 406 (mayonnaise consistency) in the seam. Use a syringe
or an 810 Caulking Tube to fill the gap with enough epoxy so that a small amount will
squeeze out when the splines are pushed in (Figure 5-3).
Figure 5-3 Push the wet-out spline into the seam.
Figure 5-4 Use a plane to remove the excess spline and a sander
to fair the surface after the epoxy has cured.
Repairing Hull and Deck Planking
4. Push the wet-out spline into the seam (Figure 5-4). The taper on the spline should force
epoxy to the sides, making good contact with the spline and edges of the planks. The
spline should fit snugly in the seam with hand pressure after a small amount of epoxy
squeezes out of the joint. Staple the spline if necessary to hold it in position.
5. Clean up excess epoxy. Use a sharpened mixing stick to scrape up excess epoxy before
it cures. Station a helper inside the boat or check the inside frequently to clean any
epoxy leaking through the planking.
6. After the epoxy cures thoroughly, remove the excess portion of the spline with a plane
followed by coarse sandpaper (Figure 5-5). Fill the vertical seams and any remaining
voids with epoxy/407 fairing compound before final fairing and finishing.
7. Important! Coat the exterior following the procedures in Section 7. Failure to apply an
epoxy moisture barrier may cause structural damage when planks swell. Fiberglass
cloth is often applied to provide additional reinforcing and abrasion resistance.
5.1.3 Filling the seams with epoxy.
A quicker but more expensive way of bonding the seams is to fill the entire gap with
thickened epoxy (epoxy is more expensive than wood by volume). This method is
more practical on seams that are too curved or tight for a spline.
1. Open the seam as before. The gaps do not have to be a particular width, as long as you
expose fresh wood on each plank edge.
2. Wet out the gap with resin/hardener mixture.
3. Fill the seam with thickened epoxy/403 (mayonnaise consistency). (Note: 403 filler
will leave an off-white colored seam, which will not matter if you plan to paint the
surface. If you plan a clear finish you may want to use 405 Filleting Blend or a coloring
agent mixed with the epoxy to match the planking color. See Section 7 for information
on finishing.) Large syringes or caulking tubes are convenient to inject the thickened
epoxy into the seams. Smooth the mixture flush with the surface and remove excess
epoxy before it cures. Check the inside for leaks and clean any excess epoxy before it
4. Sand the surface fair after the epoxy cures thoroughly. Fill any remaining low areas
with epoxy/low-density filler mixture.
5. Coat the exterior following the procedures in Section 7.
5.1.4 Repairing damaged planks in place
If you will be repairing or replacing a lot of planks, it is best to repair individual planks
and small areas completely before going on to other areas. The hull may be seriously
weakened and lose its shape if you remove too many planks at one time. Scarf joints or
butt joints can be used in repairing damaged sections of planks without removing the
entire plank. Support the hull in its proper shape before bonding.
Scarf joint method
To repair damaged sections of planks using scarf joints:
1. Remove the damaged part of the plank using a circular saw, hand saw or chisel.
2. Bevel each end of the plank opening with an 8-to-1 scarf.
3. Cut a piece of wood to fit the opening. Match the 8-to-1 bevel on each end (Figure 5-6).
Make the new piece of wood slightly thicker than the original planking. Excess
material inside or outside the hull can be planed off after the glue has cured.
4. Wet out the mating surfaces with resin/hardener mixture. Recoat the scarfed surfaces
as necessary until the end grain is fully saturated.
Repairing Hull and Deck Planking
Figure 5-6 Replace a section of plank using scarf joints.
5. Apply thickened epoxy/403 or 406 (peanut butter consistency) to one side of each
bonding area.
6. Clamp the scarfed section in place with temporary screws or staples until the epoxy has
cured. Corrosion-resistant screws can be left in if the pilot holes were wet out with
7. Remove clamps and fair the surface after the epoxy has cured thoroughly.
Butt joint method
The butt joint is an alternative to the scarf joint for repairing damaged planks in place.
Although not as strong as the scarf, it is considerably easier to do. Butt joints should be
staggered (adjacent planks should not end at the same place). To repair a damaged
plank section using butt joints:
1. Remove the damaged portion of the plank using a circular saw, hand saw, saber saw or
2. Cut a replacement piece of wood for the opening and a piece for a backing plate (Figure
5-7). A backing plate will be required behind each butt joint unless the joint falls on a
frame. When the repair section falls between frames, the backing plate should run from
frame to frame. When replacing longer sections of planking, a backing plate is only
required at the ends.
Figure 5-7 Replace a section of plank using butt joints.
Repairing Hull and Deck Planking
3. Wet out all mating surfaces with resin/hardener mixture.
4. Apply thickened epoxy/403 or 406 (peanut butter consistency) to the mating surfaces
(including the surface of the backing plate facing the plank).
5. Install the backing plate(s) to the back of the planking. Temporarily clamp the backer
in position with screws, staples or nails.
6. Install the new plank section. Clamp the section in position with screws, staples or
nails. Fill remaining openings in seams with thickened epoxy.
7. Remove clamps and fair the surface after the epoxy has cured thoroughly.
5.1.5 Double Planking
Repairs to double planked boats involve removing the outer layer of planking,
repairing the inner layer following the procedures already described in Section 5.1,
and then replacing the outer layer of planks. Removing both layers of planking is
desirable in that it allows you to examine the planks thoroughly and seal them
completely in epoxy. If you wish to coat the inside of the hull with epoxy, you need to
remove both layers of planking, clean and strip them of paint, and rebond them to the
framing timbers. Remember you can only encapsulate the boat with epoxy if all of the
surfaces, especially the contact surfaces of joints, can be coated.
To repair double planking:.
1. Carefully label the outer layer of planking for position and remove it.
2. Decide if the planks are worth saving. If so, clean, dry, repair and sand them.
3. Remove and discard the canvas between the layers of planking.
4. Follow the procedures described in 5.1.1–5.1.4 to clean out the seams and bond the
layer of planking still on the hull.
5. Bond the second layer of planking, following techniques discussed in 8.4.2. You can
use screws in the old screw holes to hold the planks in place while the epoxy cures.
5.1.6 Repairing Tongue and Groove Deck Planking
The methods described previously are also applicable to tongue and groove deck
1. Clean the seams to the tongue.
2. If access is possible and the tongue is loose or broken, tape the underside of the seams.
3. Force thickened epoxy\403 or 406 (mayonnaise consistency) as thoroughly into the
seams as possible. This mixture, forced with a 5" wide putty knife, can flow about the
tongue and groove joint and into the underside seam, thereby achieving a complete
bond of the mating planks.
5.2 Lapstrake Planked Hulls
Lapstrake (or clinker), like carvel planking, is composed of a single layer of planks thin
enough to bend to the shape of the hull. However, each plank (or strake) overlaps the
face of the preceding plank rather than butting the edge of it. Wooden lapstrake hulls
often have trouble with the lap fasteners working seams open, causing leaks. The most
successful repair is to clean out the lapped seams and bond the planks together with
epoxy. It will be very helpful to work on your boat upside down if it is small enough to
turn over. Repair lapstrake hulls as follows:
1. Remove all paint or old finish on the outside of the hull.
Repairing Hull and Deck Planking
Figure 5-8 Clean out the seams with a scraper.
Figure 5-9 Fill the wet-out seam with thickened epoxy
2. Scrape the old paint and caulk out of all the seams. Use a custom scraping tool to clean
out and abrade the plank mating surfaces down to bare wood (Figure 5-8). A file with
the tang bent and sharpened or a hacksaw blade makes an excellent seam scraper.
Allow the wood to dry thoroughly if it has not already dried. Support the hull in its
proper shape before beginning bonding.
3. There is typically a transition from the lap to a rabbet where the planking laps run into
the stem or transom. This allows the planks to lie flush with each other and fair with the
stem. When cleaning out the laps, pay attention to this transition zone. It may be
necessary to remove fasteners at the ends of the planks and open them slightly to clean
out the seams and the rabbets.
4 Wet out the opened seam surfaces with resin/hardener mixture. Work epoxy into the
seam as deeply as possible with a disposable brush or syringe.
5. Apply thickened epoxy/403 or 406 (peanut butter consistency) into the opened seams.
Use a plastic spreader to force the thickened epoxy into the seam as far as possible
(Figure 5-9). Check inside for epoxy leaking through the planks. Clean excess epoxy
before it cures.
6. Shape the thickened epoxy at the inside corner of the seam to a square inside corner or
a cove-shaped fillet. A fillet increases the bonding area around the seam and provides
more protection to the edge of each plank. For more details on fillets see Section 8.4.3.
7. Sand the seams and plank surfaces fair after the epoxy has cured thoroughly. Fill and
fair any remaining voids with an epoxy/low-density mixture. Follow the
coating/finishing procedures in Section 7.
5.3 Plywood hulls and decks
Plywood has a high strength-to-weight ratio and makes an excellent boat building and
repair material. Douglas Fir is the most common wood species used in plywood.
Exterior construction grade plywood, available at lumberyards, has been used for boat
building and repairs, but if the boat is going to see offshore service, we recommend a
higher grade of plywood. Medium Density Overlay (MDO) is used by some boatbuilders
because the resin-impregnated paper face provides a smooth base for paint and epoxy.
AA marine grade is the highest quality Douglas Fir plywood for marine repairs.
Mahogany plywood is the highest quality and first choice if the high costs are
Repairing Hull and Deck Planking
Use a syringe to fill all voids (found in lesser grades of plywood) with thickened epoxy
after cutting the panel to final shape. Lesser grades of Douglas Fir plywood may
require a layer of fiberglass cloth to prevent grain checking.
5.3.1 Rebuilding a plywood joint
If the seam between plywood sheets has deteriorated, you can clean out the joint, seal
the edges with epoxy and reinforce the joint with fiberglass tape applied with epoxy.
The seam may be on a flat surface or at an edge or chine. Rebuild a plywood joint as
1. Clean out the seam by running a circular saw or scraping tool along the seam. Set the
depth of the saw cut to the full thickness of the plywood when the seam runs along a
frame. Set the width of the blade to shave the edges of both sheets of plywood at the
joint and expose fresh wood on each edge. Remove any fasteners in the way of the cut.
Be sure the wood is thoroughly dry.
2. Drive the fasteners deeper at the joint to allow for a valley to be sanded along the joint
for the placement of one or more layers of fiberglass tape.
3. Sand a 4" to 5"- wide valley along the joint with a disc sander to allow the layer(s) of tape
to lie below the surface. Make the depression about 1 32" deep for each layer fiberglass
tape that will fill the joint. Use the sander or a chisel to remove any additional damaged
or rotted plywood around the joint. At an edge or chine, use the sander or a router with a
roundover bit to round the corner. A 1 4" to 3 8" radius will allow the glass tape to lie flat on
the surface (Figure 5-10).
4. Wet out the cleaned out seam and sanded area with resin/hardener mixture. Recoat the
seam with epoxy as necessary as it is absorbed into the end grain of the plywood. Inject
or work epoxy between any delaminated veneers that are still sound.
5. Apply thickened epoxy/403 or 406 (mayonnaise consistency) to the seam. Use a plastic
spreader to force the thickened epoxy into the wet-out seam and smooth the excess
mixture along the joint. Work the thickened mixture into any voids and between
wet-out delaminated veneers.
6. Apply a layer of fiberglass tape in the depression along the joint (Figure 5-11). 727
Biaxial Tape (4" wide) is ideal for this joint. Use the spreader to work epoxy into the
fabric and remove the excess. Apply additional layers, if desired, in the same manner.
Figure 5-10 Sand a valley along the joint to allow for fiberglass
Figure 5-11 Apply fiberglass tape over the prepared joint.
Repairing Hull and Deck Planking
Place new layers ½" to either side of the previous layer so the edges don’t fall directly
on top each other. For details on applying fiberglass cloth, see Section 8.4.5.
7. Apply thickened epoxy/407 or 410 low-density filler (peanut butter consistency) to the
joint. Use a plastic spreader to trowel on and shape the thickened mixture slightly
higher than the plywood surface (Section 8.4.4). Allow to cure thoroughly and sand
5.3.2 Replacing damaged plywood sections.
Sections of plywood panels may suffer from impact or dry rot damage and can be
repaired without replacing the whole panel. The damaged section can be cut out and a
replacement section bonded in without losing any panel strength. Replace small
plywood panel sections as follows:
1. Cut the damaged section out of the panel. Use a circular saw or reciprocating saw to cut
the smallest square or rectangle that encloses all of the damage. Check the extent of
damage on the interior of the panel.
2. Scarf or step the edges of the opening.
a. Grind a scarf on the edges with a disc sander (Figure 5-12). Grind a minimum 8-to-1
bevel back from the edges of the opening. (If the panel plywood is ½" thick, the bevel
should extend at least 4" from the edge of the hole on each side.)
b. Mill a step on the edges of the hole with a router. Use a straight fluted bit to machine
a step or steps in the panel round the opening. The width of each step should be eight
times the step thickness. Steps are convenient when laminating several layers of thinner
plywood to equal the thickness of the damaged panel. Make each step equal to the
thickness of one replacement layer.
Figure 5-12 Cut out the damaged area and grind a minimum 8to-1 bevel on all sides of the opening.
Figure 5-13 Clamp a new repair patch in position with staples
or screws.
3. Fabricate the replacement panel using the same or equivalent plywood as the original.
Cut the panel to the outside dimensions of the bevel or step.
a. Use the disc sander to machine a bevel on the inside edge of the replacement panel to
match the bevel on the opening. Dry fit the new panel to fit slightly below the existing
surface (Figure 5-13).
b. Use the router with the straight fluted bit to machine steps in the edges of the
replacement panel to match the steps around the opening. If multiple layers of
Repairing Hull and Deck Planking
plywood are to be used, cut one layer to the dimension of each step. Dry fit the new
panel to fit slightly below the existing surface.
4. Wet out the bonding area of the panels with resin/hardener mixture. Recoat the end
grain as necessary. (Plywood end grain will absorb a lot of epoxy.)
5. Apply thickened epoxy/403 or 406 (mayonnaise consistency) to the new panel’s
bonding area. Apply enough thickened epoxy so that a small amount will squeeze out
when you push the new panel into its dry-fit position.
6. Clamp the new panel in position with temporary staples or screws. Permanent
fasteners should be non-corroding and pilot holes should be wet out with epoxy. Clean
up excess epoxy before it cures. Allow the epoxy to cure thoroughly before removing
clamps. Bond multiple thinner layers in place, one at a time, following the same
procedure. Use a thinner epoxy mixture on the flat bonding areas between the layers.
7. Sand the surface and fill low areas with epoxy/407 or 410 low-density filler (peanut
butter consistency). Use a spreader to apply the thickened epoxy, slightly overfilling
low areas on the surface. Allow the mixture to cure thoroughly before fairing.
5.3.3 Replacing/installing plywood
You may install new plywood over exposed frames or over existing hull or deck
surfaces. Plywood used as the primary skin (bonded directly to the frames) may be laid
out with scarfed joints falling directly over the frames or with butt joints over backing
plates between the frames. Scarfed joints offer a cleaner appearance from the interior.
The frame spacing and size of the boat determine the thickness of the plywood. The
amount of compounding determines whether the total thickness can be applied in one
layer or in multiple layers. Apply thinner plywood in multiple layers if one layer is too
thick to bend over a curved surface. Apply a primary plywood skin as follows:
1. Prepare plywood panels, scarf joints and beam surfaces. Plan the panel layout and
order of assembly so that the scarf on the following sheet lies over the scarf on the
previous sheet (Figure 5-14 ).
2. Wet out the bonding surfaces of the plywood and frames. Wet out scarfs on the ends of
adjoining sheets.
3. Apply a coat of thickened epoxy/406 mixture to the bonding surfaces of the frame and
the scarf of the previous sheet.
4. Lay the sheet in position over the frames. Align the scarf joint to avoid overlapping.
Figure 5-14 Plan the panel layout so that scarf joints will fall over beams for better clamping.
Repairing Hull and Deck Planking
5. Clamp the sheet temporarily with drywall screws or staples. Use enough fasteners to
clamp the sheet evenly. The epoxy mixture should squeeze out of the joints, assuring
good adhesive contact. Station someone inside to clean excess epoxy at the frames and
joints. The excess can be scraped clean or shaped into a fillet before it begins to cure.
6. Repeat the process with the remaining sheets. Allow the joints to cure thoroughly
before removing temporary fasteners.
7. Sand the joints and fair the surface before adding another layer of plywood,
fiberglassing (Section 8.4.5) or finishing (Section 7).
5.3.4 Applying plywood over existing skins
When laminating an additional layer of plywood over an existing hull or deck, it’s not
necessary to scarf joints or place joints directly over frames because of the large
bonding area. Restore existing plywood to sound condition before laminating new
sheets over it. Laminate new plywood over an existing deck or hull as follows:
1. Rebond delaminated layers of plywood, after drying thoroughly. Drill a pattern of 1/8"
holes in the delaminated area. Use a syringe to inject a slightly thickened epoxy/406
mixture in all of the holes to reach all of the delaminated area. Use staples or screws to
clamp the layers together until the epoxy cures. When the epoxy has cured thoroughly,
proceed with Step 2.
2. Sand the surface fair to clean, bare wood. Remove all old finishes and contaminants.
3. Open existing joints with a scraper, saw or router and fill the joints with epoxy. Repair
with fiberglass tape, if necessary, as suggested in Section 5.3.1.
4. Cut out severely damaged areas and scarf in new plywood, if necessary, as suggested in
Section 5.3.2.
5. Plan the layout of the new plywood sheets to avoid new joints falling over existing
6. Apply an epoxy/406 mixture to both bonding surfaces with a roller. Thicken the
mixture to a catsup consistency to allow some penetration and still bridge any gaps
between the surfaces. If the surface is rough or uneven, thicken the epoxy mixture to a
mayonnaise consistency and apply with a notched spreader.
7. Clamp the sheet in position with an even pattern of temporary screws or staples. Clean
up excess epoxy at the joints. Repeat the procedure with each sheet. Allow the epoxy to
cure thoroughly before removing temporary fasteners.
8. Sand the surface fair before final finishing.
5.4 Molded or laminated veneer repairs
Another option for skin covering uses strips of thin veneer instead of sheets of
plywood. Laminated boats were and are being built by gluing layers of thin veneers
together over curved forms, in effect building a sheet of plywood in the shape of a boat.
This technique has produced lightweight rigid hulls that aren’t limited to the flat
surfaces and hard chines of plywood boats. Using veneers for skin repairs offers the
advantage of being able to conform to any curved shape, especially compound curves.
This advantage can be used for repairs in several ways. Veneers can be used to patch
small sections of laminated hulls that are too curved for a plywood patch. On a larger
scale, laminating layers of veneer over an existing plywood or carvel planked hull is an
excellent method of adding a lot of stiffness to a hull or deck without removing the
existing skin. More detailed information about laminating veneers as a building
technique can be found in 002 The Gougeon Brothers On Boat Construction.
Repairing Hull and Deck Planking
5.4.1 Laminating a curved patch in place
Laminating a patch for repairing a molded panel combines two procedures already
covered: repairing damaged plywood sections and laminating frames. Laminating a
curved panel section in a large damaged area requires temporary backup stringers to
act as a jig. Laminate the patch in place as follows:
1. Remove the damaged section of the panel. Define the area of damage. Use a circular
saw or reciprocating saw to cut the smallest square or rectangle that removes all of the
damage (Figure 5-15). Check the extent of damage on the interior of the panel as well.
Figure 5-15 Remove the damaged section. Figure 5-16 Bevel the edges and fasten
Figure 5-17 Cover the stringers with plastemporary stringers to the back of the open- tic to prevent bonding. (View from inside of
2. Scarf the edges of the opening with a disc sander. Grind a minimum 8-to-1 bevel back
from the edges of the opening. (If, for example, the panel plywood is ½" thick, the
bevel should extend at least 4" from the edge of the hole on each side.)
3. Fasten temporary stringers to the back side of the opening with screws (Figure 5-16).
The stringers should be strong enough and spaced closely enough to hold the veneers
to the proper shape. Cover the stringers with plastic to prevent bonding (Figure 5-17).
4. Staple the first layer of veneers over the stringers. Run the veneers diagonally,
approximately 35° from vertical. Scarf the ends of the veneers to match the scarf on the
edge of the opening. Bond these first layer veneers only where the scarfs make contact,
using the bonding procedure in Section 8.4.2. Use 403 or 406 filler to thicken the
epoxy to a mayonnaise consistency.
Figure 5-18 Bond the second layer in the opposite diagonal to the first layer.
Figure 5-19 Continue until all the layers are
completed, matching the skin thickness.
Repairing Hull and Deck Planking
5 Bond the second layer of veneers after the first layer has reached a partial cure, or a full
cure with sanding (Figure 5-18). Run the veneers diagonally in the opposite direction,
about 35° from vertical. Remove the staples only in the area under the veneer being
bonded. Coat the face of the new veneer and the contact area of the first layer including
both scarfs. Staple through the veneers into the stringers and at the scarfs as necessary
to hold the veneers flat.
6. Continue until all the veneers are in place and you’ve matched the thickness of the
original skin (Figure 5-19). By removing the staples in the previous layer only under the
new veneer, all previous layers of veneer will stay in place even though the epoxy has
not thoroughly cured. This will allow you to bond several layers of veneers in one
continuous operation. Be sure the staples are long enough to provide clamping
pressure by penetrating to the stringers or veneers that have cured fully. Allow the final
layer to cure thoroughly before removing staples, fairing and final finishing.
5.4.2 Laminating a patch away from the damaged area
A panel section also can be repaired by using the existing skin as a form to laminate a
patch panel and then bonding the pre-formed patch in, in one piece. The size of the
patch should include the damaged area plus an 8-to-1 scarf beyond the damaged area.
Tape a sheet of plastic over and beyond the area you wish to use as a mold surface. An
adjacent area that is curved slightly more than the damaged area is an ideal mold
surface because it compensates for veneer springback during molding (Figure 5-20).
After laminating the appropriate number of veneers to equal the size and thickness of
the damaged section (plus scarf), prepare matching scarfs on the damaged area and the
patch. Then bond the patch into place using the procedure described previously in
Section 5.3.2.
Figure 5-20 Laminate a replacement panel using the surface next to the damaged area as a
5.4.3 Laminating a new skin over an old skin.
The technique of laminating one or more veneers over an existing hull has breathed
new life into many boats that otherwise would have been given up for dead. The
thickness and species of the new skin depends on how much strength is left in the old
skin. If the hull can be supported in the proper shape, the new skin could replace the
function of the old skin entirely. After you’ve established the total thickness and type of
wood, determine the thickness and number of layers of veneer. As a rule, use the
thickest and fewest layers of veneers that can bend and clamp to the tightest curves on
Repairing Hull and Deck Planking
the hull. Bonding all the seams of a planked hull before adding veneers to the hull will
add stiffness and reduce the total thickness of veneers required (see Section 5.1).
Laminate veneers to an existing skin as follows:
1. Prepare the existing hull for bonding. Be sure the surface is clean, dry and sanded.
Support the hull in its proper shape. Fill and fair low areas that are too big for the
veneers to bridge. Grind off any high spots that could keep the veneers from lying flat.
2. Bond the first veneer about midpoint on the hull. Use the one-step bonding technique
(Section 8.4.2) with an epoxy/403 filler mixture. Staple the veneer so it lies flat against
the surface at about a 35° diagonal (Figure 5-21). Adjust the angle as necessary to allow
the veneer to lie flat along its full length.
Figure 5-21 Bond the first layer at an angle that allows it to lie flat against the surface.
Figure 5-22 Bond the second layer of veneers in the opposite diagonal to the first layer.
3. Bond the remaining veneers of the first layer. Trim the second veneer to fit tight against
the first and lie flat against the surface. The ends of the veneer may have to be tapered if
the surface is a compound curve. Bond and staple the second veneer in place. Continue
trimming and bonding veneers in each direction from the first veneer.
4. Sand the surface fair after the epoxy cures thoroughly. Staples should be removed
before sanding unless they are a non-corroding type which may be left in.
5. Repeat the process on the second layer (Figure 5-22). Begin with the first veneer about
midpoint at a 35° diagonal in the opposite direction to the first layer. Trim and bond
the remaining veneers.
6. Repeat the process on the remaining layers. Remove the staples after the last layer has
cured. Sand the surface fair and prepare it for final finishing.
Repairing Hull and Deck Planking
5.5 Installing a teak veneer deck
Thin strips of teak bedded in a thick epoxy/graphite layer give you an authentic teak
deck that is both durable and low in maintenance. Although strips of up to ¼" thickness
may be used, the effects of dimensional change can be limited by using thinner,
8"-thick strips. A 8"-thick deck will provide you with years of service in high-traffic
areas, and it will keep the additional weight of a new teak deck to a minimum. Strips
should be between 1½" and 2" wide, with edges planed smooth and straight. Leave the
flat surfaces (top and bottom) rough sawn. The rough texture left by the saw improves
the bonding characteristics of the strip. The remaining marks on the exposed surfaces
will be sanded smooth after the new deck has been laid.
If you plan to mill your own stock, select a plank width that makes the most efficient
use of the raw stock. Teak is generally available in 2"-thick, rough-sawn planks; you
should get close to a 1¾" finished dimension from these planks. Saw the stock so that
the strips will be edge-grained (Figure 5-23). This will minimize expansion and
contraction of the wood and make a more attractive, even-wearing surface than will
slab-grained strips. Moisture content should be between 6% and 10%. Install a teak
deck as follows:
Figure 5-23 Thin edge-grained strips provide an even wearing, attractive and dimensionally stable
1. Plan the pattern for the layout of the teak strips. Place the first teak strips in the desired
location and then mark reference location points on the strips and on the deck.
2. Abrade any smooth bonding surfaces with 50-grit sandpaper and remove sanding dust.
Wipe the planks with paper towels saturated with acetone or lacquer thinner 30
minutes before bonding.
3. Wet out the mating surface of the first few pieces of teak and the deck in the area of the
first few strips with unthickened resin/hardener.
4. Apply a thickened epoxy mixture over the wet-out deck surface. Use 404 High-density
filler (thickened to catsup–mayonnaise consistency depending on deck fairness) and
add just enough 423 Graphite Powder to turn the mixture to an opaque black color.
Apply a layer just thick enough to span any gaps and to squeeze up between the planks.
An 809 Notched Spreader works well to apply an even layer over the substrate.
5. Locate your reference points and set the first strips in place.
Repairing Hull and Deck Planking
6. Clamp the plank in place with #10 sheet metal screws and large washers. Place the
screws and washers between the strips, 8" apart. Each row of screws will clamp the
edges of two adjoining planks and act as spacers (Figure 5-24 left). Coat the screws and
washers with a mold release or place a small sheet of plastic under the washers to
prevent bonding. Washers may also be cut from stiff plastic, thin wood lathe or similar
stock with holes drilled for the screws. Tighten the screws down completely after
pushing both adjoining strips tight against the screws. The epoxy mixture should
squeeze up between the strips. Any voids between the planks should be filled at this
time with the epoxy/404/graphite mixture.
Figure 5-24 Sheet metal screws with large washers will clamp the strips in position until the epoxy/404/graphite mixture cures thoroughly.
7. Place the remaining strips, several at time, following the same procedure.
8. Allow the epoxy to cure between 8 and 24 hours before removing the screws and
washers. If you wait any longer than this, it will become much harder to break the
screws free. Tighten the screw slightly (5°) before backing it out. If you have difficulty
removing a screw, heat the head with a soldering gun’s cutter tip. While the screw is
still hot, try to unscrew it again. Repeat until you are successful.
9. Fill the screw holes with epoxy/404/graphite mixture. A syringe loaded with the
mixture will speed the process.
10. Sand the surface with a reciprocating sander and 50-grit sandpaper to level the epoxy
and teak surfaces. Sand until the saw marks are removed from the teak surface. Fine
sand with 80-grit sandpaper, and then finish with 120-grit. The teak surface may be left
natural or finished with a marine-grade teak oil.
Note: If planks thicker than 1 8" are used, do not fill between the planks with thickened
epoxy. Instead, remove squeezed-out epoxy between planks and allow to cure.
Remove the screws and washers and sand the top surface of the planks fair. Fill the
joints with Thiokol or polysulfide caulk (Figure 5-24 right).
Installing Hardware
6 Installing Hardware
Now that the deck is upgraded, the hardware should receive the same thorough
attention. To overcome problems associated with hardware installation on wooden
boats, Gougeon Brothers, Inc. has developed an approach called hardware bonding. As
the name implies, hardware items are bonded (glued) to wood with the goal of
distributing high, single-point loads over as large an area of wood fiber as possible,
while allowing the epoxy to seal and protect the wood end grain exposed by the
fastener hole. Note: the term “hardware bonding” as used in this manual does not refer
to the electrical bonding of hardware to eliminate stray current corrosion.
There are two ways to do this. The first is to bond all fasteners (screws, bolts or
threaded rod) directly to the surrounding wood fiber. The second is to bond both the
fasteners and the hardware itself to the immediate wood fiber on which it rests. Using
proper hardware bonding installation techniques, you can dramatically improve the
load-carrying capacity of your hardware over that possible with standard hardware
installation methods.
In saltwater applications, our experience has been that bonded hardware and fasteners
show excellent resistance to corrosion attack. Where fasteners are vulnerable to
flexure and saltwater attack (e.g., hollow or bridged traveler tracks, bonded U-bolts or
solitary eyebolts) a small silicone sealant fillet covering the joint between the cured
epoxy and the fastener will protect against moisture and salt intrusion. Of course, any
exposed metal surface will be subject to the effects of saltwater corrosion; therefore
proper maintenance and cleaning procedures must be practiced.
6.1 Fastener bonding
The fastener-to-wood bond can be done in several ways. The easiest and most common
method is simply to wet out a standard-size pilot hole for a given fastener with
resin/hardener. Make easy fastener bonds as follows:
1. Use a pipe cleaner or syringe to work the mixture well into the hole.
2. Insert the fastener in the hole and allow the epoxy to cure.
This forms a wood/epoxy matrix around the fastener that is much stronger than the
wood by itself, and distributes the fastener load over more of the wood fiber area.
6.2 Hardware bonding
You can further improve the load-carrying capability of the hardware by increasing the
amount of epoxy that surrounds the fastener (taking advantage of the fact that WEST
SYSTEM® epoxy has much higher density and strength than the wood fiber itself) and
bonding the hardware base directly to the surface. Bond for increased load transfer as
Installing Hardware
Figure 6-1 A normal sized pilot hole at the bottom of the oversized
hole provides enough clamping pressure to hold the hardware in position
until the epoxy cures.
Figure 6-2 Tighten the fasteners until a small amount of
epoxy squeezes from the joint.
1. Drill an oversized pilot hole to increase the amount of exposed wood area that the
epoxy around the fastener will bond to. This may be much larger than the
fastener—twice the fastener diameter, for example. Drill the hole 2/3 to 3/4 the depth
of the fastener.
2. Drill a normal sized pilot hole at the bottom of the oversized hole to the full length of
the fastener (Figure 6-1). This allows the bottom threads of the fastener to bite into the
wood fiber so the fastener will stay in proper position until the epoxy cures.
3. Prepare the hardware by washing the contact surface of the base with solvent to
remove any contamination. Abrade the contact surface with a wire brush or 50-grit
sandpaper to allow the epoxy to “key” into the surface.
4. Fill the holes to the top with epoxy. Allow the epoxy to soak into the exposed end grain
of the wood for a few minutes. If the hole remains filled after 5 minutes, remove the
epoxy with the syringe.
5. Coat the bottom contact surface of the hardware with unthickened epoxy. Wire brush
or sand the wet epoxy into the surface with 50-grit sandpaper. Sanding the base, coated
with epoxy, will expose the epoxy directly to fresh metal with no chance for the metal
to oxidize.
6. Inject a non-sagging epoxy/404 or 406 mixture into the hole. Use enough mixture so
there are no voids in the hole after inserting the fastener. Coat the bottom of the
hardware and the fastener threads with the thickened mixture.
7. Place the hardware in position. Insert and tighten fasteners until a small amount of the
mixture squeezes out of the joint (Figure 6-2). Do not over tighten.
8. Clean the excess epoxy mixture that has squeezed out.
9. Allow the epoxy to cure at least 24 hours before applying load to the hardware. Allow
more time in cool weather.
Bonding the contact surface of a hardware item can contribute a great deal to load
distribution over maximum wood surface area. You can use WEST SYSTEM epoxy to
make good bonds with most metals. However, careful preparation of the metal surface
is necessary for good adhesion. This includes sanding and acid etching. For example,
aluminum requires a two-step surface preparation. The first step involves the use of an
acid conditioner that removes corrosion. The second step chemically stabilizes the
surface and prevents oxidation, allowing time for coating or bonding. The WEST
SYSTEM 860 Aluminum Etch Kit contains complete instructions.
Installing Hardware
6.3 Casting epoxy bases for hardware
Occasionally, fittings must be set at specific angles to the hull or deck surfaces.
Downrigger bases, lifeline stanchions, winches and turning blocks are all good
examples. Traditionally, hand-carved, wedge-shaped shims have been used to achieve
the proper angles with such fittings. Unfortunately, wooden shims require a great deal
of time and carpentry skill. Hardware casting can save time and is easy to do; more
importantly, it can result in a stronger, waterproof base. Cast the hardware at an angle
to the surface as follows:
1. Prepare the bonding surfaces. Clean the substrate and hardware bonding surfaces with
solvent to remove any contaminants. Sand the deck with 50-grit sandpaper. Apply a
release agent, such as an automobile wax or a non-stick cooking spray, to the base of
the hardware.
2. Position the hardware. Mark the outline of the hardware and shim it to its desired
angle. Mark the shim locations. Often one edge of the fitting will rest on the deck and
become the zero point for the required angle.
3. Wet out the substrate (deck) surface with resin/hardener mixture except for the shim
4. Cast epoxy supports under the hardware (Figure 6-3a). Prepare a mixture of
resin/hardener/404 High-Density filler (peanut butter consistency). Use the mixing
stick to place three portions of the mixture within the hardware outline, evenly spaced
around the perimeter. Use enough of the mixture and pile the mixture high enough to
contact the base of the hardware when it is shimmed in its proper position. When
cured, the epoxy supports will take the place of the temporary shims. Set the fitting in
place with the temporary shims holding the hardware at the proper height and angle.
The bottom of the hardware should contact all three epoxy supports. Allow the epoxy
supports to cure thoroughly.
5. Tap the hardware with a mallet to break it loose and remove the temporary shims.
Mask off the area around the fitting with duct tape and plastic in case of accidental
epoxy spills.
6. Prepare the deck and hardware for casting the base. Wash and sand the cured epoxy in
the deck base area. Reapply mold release to the hardware base. At this time, mask off
areas of the hardware that you don’t want to come in contact with the epoxy. You may
also find it helpful to place small pieces of tape over the holes in the hardware item to
prevent the epoxy mixture from oozing up through them when the piece is
7. Apply enough thickened epoxy/404 (peanut butter consistency) to fill the entire base
area. If the base to be cast is more than ½" (12mm) thick, you may want to use 206 Slow
Hardener to reduce the possibility of exothermic heat buildup during the curing
process. Build up the mixture slightly taller than the base supports, roughly forming
the shape of the base. Fill all voids around the epoxy supports.
8. Reset the hardware in its proper location. Slowly press it into the proper position on
top of the cast epoxy supports. Allow excess epoxy mixture to squeeze out of the gap
between the base of the hardware and the deck. Sculpt the squeezed out mixture into
the desired shape (Figure 6-3b). A standard fillet works well in this situation (Section
8.4.3). Add extra mixture if necessary for shaping or to fill any voids. Remove any
excess before it cures. Allow the epoxy to cure thoroughly.
9. Tap the hardware with a mallet to remove it from the base. Clean the bottom of the
hardware and the top of the cast base with solvent to remove the mold release. Sand
both bonding surfaces with 50-grit paper.
Installing Hardware
Figure 6-3 Hardware casting is an excellent method for installing a piece of hardware that is not flush to the deck such as a winch.
10. Sand the cast base to the desired final finish. Begin with 50-grit sandpaper or a file if the
base is extremely irregular. Finish with 80-grit sandpaper.
11. Bond the hardware to the cast base using the hardware bonding procedure in section
6.2 (Figure 6-3c). Drill oversized and standard pilot holes for the fasteners through the
cast base. Allow to cure thoroughly before applying loads to the hardware. Apply three
coats of resin/hardener mixture to the base before final finishing.
6.4 Bonding studs
Bond threaded rods or studs into the substrate (instead of bolts or screws) and attach
the hardware with nuts. This variation is appropriate for many engine, motor or
machine installations. Coat the base with wax/mold release to make the hardware
removable. Although the hardware is not “bonded” to the substrate, the epoxy still
provides a bearing surface that perfectly matches and supports the base of the
Figure 6-4 Bond threaded rods or studs
into the substrate as an alternative for easily
removable hardware.
1. Prepare the studs/threaded rods by waxing the upper ends (above the surface) and
cleaning the lower ends (below the surface).
2. Place a nut and washer on the studs, wet out the lower ends and push them into the
epoxy filled holes. Allow the epoxy to cure thoroughly before tightening the nuts
(Figure 6-4).
Installing Hardware
6.5 Removable hardware
Testing at Gougeon Brothers, Inc. has shown that with bonded fasteners (screws, bolts,
threaded rods, etc.), the adhesive bond to the metal is not as important as the “keying”
between the epoxy and the threads of the fastener. This factor allows the builder to
coat the fastener with a thin film of mold release before bonding to permit easy fastener
removal after the epoxy cures.
Fatigue tests of bonded threaded rods with and without a thin coating of mold release
show only a 4-10% reduction in the overall fatigue strength of the fastener with mold
release. A thin film mold release will yield a more predictable performance than a thick
film. Mold release may include paste wax, non-stick cooking spray, silicone spray or
hair spray. While the reduction in strength of the fastener treated with mold release is
slight, it should be taken into account when calculating hardware loads. We
recommend adhesive bonding to all hardware and fasteners rather than the use of mold
release whenever possible.
6.6 Removing bonded hardware
Occasionally it is necessary to remove bonded hardware items. At temperatures above
150°F (66°C), cured epoxy begins to lose its physical properties; the resin softens and
its bonding capacity is reduced considerably. You can use this characteristic to your
advantage when you would like to remove a piece of bonded hardware.
1. Remove all fasteners. If you used a release agent on them when you bonded the piece in
place, they should come loose without too much difficulty. If the fasteners were
bonded in, it will be necessary to apply heat to them, using a soldering iron. The epoxy
around the fastener will soften enough to loosen the fastener when enough heat is
conducted down the fastener.
2. Heat the fitting briefly with a propane torch. Protect the area around the fitting from
heat damage by covering with water-soaked plywood. Allow the heat to conduct
through the base of the hardware. A sharp rap with a mallet should be enough to
dislodge the hardware. If the fitting doesn’t break loose easily the first time, don’t force
it. Heat it a second time with the torch and try again.
3. Replace the hardware by following the procedures in Section 6.2. Redrill the fastener
holes in the existing epoxy as you would for a new installation.
Protecting and Maintaining Wooden Boats
7 Protecting and Maintaining
Wooden Boats
7.1 Sunlight and protective coatings
Sunlight poses a threat to the structure and finish of all composite boats. It attacks in
two ways: heat and ultraviolet (UV) rays. Any epoxy finishes without protective
coatings are vulnerable to rapid ultraviolet degradation. WEST SYSTEM® Brand
epoxy, including the 207 Special Coating Hardener, is not intended to be used as a
final finish. Therefore, you should cover bare epoxy that will be exposed to direct
sunlight as soon as possible with an opaque paint or a clear coating (varnish). If the
surface is to be painted, add pigment to the last two coats of epoxy to protect the
surface. Surfaces that receive indirect UV exposure, such as those below decks, will last
much longer without a protective coating than directly exposed surfaces.
While a clear coating has an inherently shorter life span than a paint finish, there is a
tradition among wooden boat owners of using clear coatings to preserve and enhance
the natural beauty of wood. For many, the major attraction of wooden boats is the
beauty of wood itself and they are willing to invest a lot of time and money to achieve
near perfection in their wood finishes.
Unfortunately, these beautiful finishes seldom last forever because of exposure to the
sun. The boats must ultimately be stripped down and redone, usually at great expense.
Because of this, owners want the finish to have the longest possible life span.
The first phase of finish breakdown is loss of gloss, so surface gloss retention is essential
for coating longevity. Clear coating breakdown by sunlight has two root causes. The
first is the gradual breakdown of the coating material. The second is the slight chemical
and physical change which takes place within the surface wood cells affected by the
sunlight through the clear coating. It is thought that this change in the wood cells
contributes to the coating failure by promoting a physical separation of an already
weakened coating from the ultraviolet-altered wood surface.
We are often asked how long a coating will last over a wooden surface. The answer is
not simple because the life span of any coating depends on many factors. We consider
the following to be the most important:
1. The number of hours of exposure to sunlight in a given climate. Cloudy climates are
less hostile than sunny climates. A southern Florida location is far worse than one in
Maine because on average the solar radiation in Florida is less filtered by the
Protecting and Maintaining Wooden Boats
Figure 7-1 Effect of color on surface temperature under sunlight.
2. The angle of the exposed surface to the sunlight. For example, a deck will receive much
more direct radiation at high noon, when the sun’s destructive UV rays are most
damaging, than would cabin sides.
3. Highly glossy surfaces are more reflective of UV rays (and thus less vulnerable) than are
dull surfaces, no matter what the color.
4. Lighter colored woods are more reflective than darker colored woods, just as lighter
colored paints are far more reflective than are darker colors (Figure 7-1).
5. Thicker clear coatings last longer and offer more protection than thinner coatings.
6. Varnishes with large amounts of UV inhibitors last much longer than varnishes without
this additive. Modern two-part polyurethane varnishes last longer than the more
traditional phenolic varnishes.
7. A high-strength epoxy resin undercoating, such as WEST SYSTEM 105/207 mixture,
when used as a saturation coat under a varnish, provides a greater life span than the use
of varnish alone. A bonus is dramatically improved moisture resistance.
Gougeon Brothers, Inc. has studied the effect of these factors through many years of
observation and experimentation with all types of finishes, particularly clear finishes.
In the laboratory, we have used a weathering machine to accelerate UV damage to
coated surfaces so that we have direct comparisons between different products, finish
Protecting and Maintaining Wooden Boats
Figure 7-2 UV test samples after 3600 hours in weathering machine.
types, surface preparations, and coating substrates in a controlled test environment
(Figure 7-2). This testing has allowed us to evaluate a wide range of variables and
samples and has guided us in the development of WEST SYSTEM 207 Special Coating
Hardener. When used with, a high quality two-part polyurethane they provide a
superior quality clear finish with excellent resistance to damage from moisture and UV
7.2 Applying the final epoxy coatings
The object of final coating is to build up an epoxy coating that provides and effective
moisture barrier and a smooth base for clear coatings or paint. A minimum of two coats
of WEST SYSTEM epoxy will provide an effective moisture barrier. Apply three coats
when sanding is required. Since sanding is required before applying the finish coating,
this is the standard practice. Apply up to five or six coats if you plan to do a lot of
sanding or want the maximum moisture barrier or a deeper finish. Each coat achieves a
3-4 mil thickness. The maximum recommended thickness is 15-20 mil.
We recommend WEST SYSTEM 207 Special Coating Hardener be used for the highest
quality, longest-lasting clear finish. 207 contains a UV filter that improves the ability of
the mixed 105/207 epoxy to resist the harmful effects of sunlight without
compromising moisture resistance. Keep in mind that although 207 is very clear, it is
not colorless. It has a light amber color similar to spar varnish that will tint wood
slightly warmer and darker. If you are not interested in a clear finish, select the
hardener (205, 206 or 209) that best meets your needs.
General procedures for final epoxy coating are listed in the WEST SYSTEM User
Manual & Product Guide. The following are specially applicable for using 207 Special
Coating Hardener to prepare for a deep lustrous finish in the fastest possible time:
1. Sand and fair the wood surface using 80-grit or finer paper. Always sand in the grain
2. Apply a saturation coat of 105/207 to the bare wood surface and allow to cure
thoroughly at room temperature. The cured saturation coat will cause the wood
surface to “swell up” and feel rough. Wash and sand or scrape the swelled wood grain
to a moderate smoothness. (Be careful to avoid sanding through this initial saturation
Protecting and Maintaining Wooden Boats
Figure 7-3 Roll lightly and randomly over a small
area. Spread the epoxy into a thin even film.
Figure 7-4 Tip off the coating by dragging a foam
roller brush lightly over the fresh epoxy.
3. Apply a second coat of 105/207 using the roller (Figure 7-3) and tip off the surface with
a foam brush. Drag the brush across the surface of the fresh epoxy in light overlapping
strokes in the direction of the wood grain (Figure 7-4). Level out the coating as much as
possible. NOTE: Apply the epoxy in thin coats. The thinner the film, the easier it is to
keep it even and prevent runs and sags.
4. Apply a third coat while the second coat is still slightly tacky. You can add any number
of coats to build up the desired coating thickness while the previous coat is still slightly
tacky. Be sure to level out each fresh coating with the foam brush.
5. Allow these coats to cure fully. The cure can be accelerated with moderate heat, but too
much heat may cause bubbling.
Figure 7-5 Wet sand to a smooth finish.
Figure 7-6 Rinse water should sheet without
beading, indicating an uncontaminated surface.
6. Wet sand the cured 105/207 epoxy surface to a 220-grit or finer finish (Figure 7-5).
Rinse the surface with clean water. Rinse water should sheet evenly, without beading
or fisheyeing. If rinse water beads up (a sign of contamination), wipe the area with
solvent and dry with paper towels, then wet sand again until beading is eliminated.
Proceed with the finish coating after the surface has died thoroughly. See Section 8.4.1,
Surface preparation, Special preparation for various materials, Cured epoxy.
7.3 Clear finish coatings
Even though a properly applied 105/207 coating may have a high gloss finish equal to
that of a good varnish, we recommend that this surface be coated with a top quality
spar varnish for UV protection and maximum performance. Two-part polyurethanes
bond well to cured WEST SYSTEM epoxy surfaces and provide great hardness and
Protecting and Maintaining Wooden Boats
durability while retaining a high-gloss, UV-resistant surface. Be sure the surface is
properly prepared, see Section 8.4.1.
1. Thoroughly mix the two-part polyurethane varnish in the proper ratio.
2. For major applications over large surface areas, always use the 800 Foam Roller which
will give a more uniform application in less time. This means runs are less likely during
application and you will have more time to do touch up.
3. Use a high quality brush with a tapered tip, 2" to 3" wide, depending on the intricacies
of the surface to be coated.
4. During application, the roller will leave a slightly stippled surface with some air
entrapped in the coating. In most instances this stipple will flow out and the bubbles
will pop on their own to leave a smooth, high-gloss surface upon cure. In some
conditions, you will need to brush out the rolled-on coating to assist the leveling
process. Do this by lightly brushing the surface with smooth, even strokes as soon as
possible after you have applied the varnish. Be aware that the time available to perform
this “tipping off” will vary by climate. Cooler temperatures should allow 5 to 10
minutes to tip off a newly applied coating with no difficulty; hot, dry conditions will
allow you less time.
For health reasons, we do not recommend spraying two-part polyurethane. Inhalation
of fumes, dust, vapors and droplets must be avoided. Spraying marine paints in general
is not recommended except if done by a trained professional with industrial grade
equipment and only in properly ventilated areas.
We are often asked how many coats of varnish you should apply. The answer is the
more the better, with the important understanding that the final coat always needs a
high gloss for longevity. Initially apply one or two coats over the 105/207 epoxy base.
Then plan to apply a new coat every year or two to assure a continued glossy surface.
This approach not only renews the surface to a high gloss, but also takes care of any
dings or scratches. Thus it has the potential to provide the longest-lasting finish before
you have to strip the surface back to bare wood and refinish from scratch.
7.4 Paint
The longest-lasting finishes are fully pigmented paints. Pigments filter out all or most
of the harmful UV rays, thus protecting the substrate. However, a slow oxidation of the
surface occurs over many years, causing it to lose its gloss. Light colored paints are
more reflective and maintain their gloss longer than darker colors. Protecting the
substrate from heat is another important reason to choose lighter colors (Figure 7-1).
We have tried many types of paint supplied by a variety of manufacturers. The more
recently developed linear polyurethanes (LP) are superior to any other paint we have
used. We recommend them as the best painting system to use over a cured WEST
SYSTEM epoxy surface. The LP systems have excellent resistance to sunlight, salt
spray and other weathering factors. They possess outstanding abrasion resistance and
hardness that can equal or surpass that of polyester gel coat. Best of all, LP paints bond
well to a cured WEST SYSTEM epoxy surface.
Until recently, most LP paint systems were designed for spray application and
application difficulties somewhat restricted their marine use. However, several of the
large paint companies have now developed brushable LP systems which we have
applied with rollers and brushes on several recent projects. While brushing may not be
quite as fast as spraying, the preparation time required for brushing is much less. Thus,
there is not a great time difference between the two methods, and in some situations
brushing could even be faster.
Protecting and Maintaining Wooden Boats
Unfortunately, LP systems pose a significant health hazard mainly due to spraying
action. LP systems contain small amounts (1% to 2%) of a highly toxic material called
isocyanate. When sprayed, this isocyanate is atomized. Most manufacturers
recommend use of a supplied air hood to prevent breathing or contacting any
contaminated air.
Brush application of LP paint systems reduces the isocyanate problem to almost
nothing because without atomization the isocyanate does not escape into the
atmosphere to be inhaled. Thus you can avoid the major obstacle to using LP systems
by applying the material with a brush instead of spraying. However, with either brush
or spray application, some solvents will escape into the atmosphere. Without adequate
ventilation of the painting area, solvent fumes from any type of paint system can be
dangerous and uncomfortable to breathe.
7.4.1 Surface glazing
Glazing or surfacing compounds often reduce finishing time. These products are much
thinner than standard puttying fillers so you can apply them quickly in a thin film over
large areas. We recommend using a wide putty knife or spreader to apply surfacer. This
technique results in a smooth surface which is not difficult to sand to a fine finish. Since
small particles of dirt can interfere with your finish, be sure your wood is clean before
applying these products.
Surfacing compounds have an advantage over primer paints in that surfacers are
high-solids materials and can be used easily to fill small voids and depressions in a cured
resin surface. Often the choice is between sanding away small air holes and valleys or
filling them. Extra sanding takes time and may remove too much protective coating, so
surfacing compounds are a good alternative.
Paint companies market surfacing compounds with instructions for their use. If you
will be using a linear polyurethane (LP) paint system, be sure to select a surfacer which
can be used under the paint. (LP paint systems use aggressive solvents which can lift
some coatings or fillers.) When using surfacing compounds, be aware of the
consistency of the compound as you are applying it. If it is too thick, it will be difficult
to apply in a controlled thin film and cause some buildup on the surface. If it is too thin,
you will lose filling power. However, it is better if the compound is on the thin side
because you can always apply another coat if the first was not sufficient, and this is
faster than sanding. You can control surfacing compound consistency by adding the
manufacturer-recommended amount of thinner. You may have to do this at regular
intervals to make up for the evaporation of thinner as you apply the compound. For
best results, use a drywaller’s taping knife, 6" to 8" wide. Make sure that the surface to
which you are applying the compound is clean.
7.4.2 Primers
We find that we rarely need primer paints when we coat hulls with WEST SYSTEM
epoxy. Primers can’t, of course, be used on naturally finished hulls, but even on painted
surfaces they don’t greatly reduce finishing time.
Primers are not usually needed to help bond a paint film to a cured WEST SYSTEM
epoxy surface. Most finish coatings adhere to an epoxy-coated surface that has been
sanded well, although interfacing primers are required with some specialized bottom
paints. If the instructions on your paint or varnish recommend a primed surface, sand
the epoxy coating until it is no longer glossy and follow the directions given by the
manufacturer for preparation. Test the product in an inconspicuous area to be sure
that it will bond to epoxy. If any product fails to dry within the period specified on its
packaging, try a different brand or use a primer.
Protecting and Maintaining Wooden Boats
Primers are sometimes used to make sanding quicker. The theory is that primers are
easier to sand than epoxy; while this may be true in some situations, you must weigh
the benefit against the time needed to apply the primer and to get an even surface.
Primers are difficult to apply evenly with a roller or brush, are unsafe to spray, and do
not flow out as well as WEST SYSTEM epoxy, so a good deal of sanding is needed just
to get the primer as smooth as the original rough-sanded epoxy surface.
A colored base coat will ease final fairing by serving as a guide to prevent oversanding
and will also reduce the number of coats of paint needed to cover an unpainted surface.
When we plan to paint a hull, we add WEST SYSTEM Color Pigment to our final coat
of epoxy, and use this instead of primer as a tracer coat.
7.5 Repairing dings and cracks
After repair or restoration, continue to inspect your boat carefully for damage. Look
for hairline cracks at the joints. There will probably be some in the first year after the
repair. See if boat flexure is the source of the crack or if moisture intrusion is causing
expansion and cracking. You do not need to repair these cracks instantly. When you
pull out your boat in the fall, sand or scrape the cracks slightly and allow the area to
dry. Repair the epoxy coating and replace any paint or varnish used over it.
Touch up dings to the varnish or paint to maintain their effective moisture and UV
barriers. Plan to apply a new coat of varnish every year or two. The linear
polyester/polyurethane coatings do not take buffing like a gelcoat so we recommend
careful application. The acrylic/polyurethanes can be buffed but seem less durable.
7.6 Ventilation for longevity
Ventilation is a key factor in the continued longevity of your boat. Keeping the boat’s
interior as dry as possible is the best preventive maintenance for preserving the
structure and making the boat more comfortable.
Keep the bilges as dry as possible. This is a good idea whether or not you have coated
the bilges with epoxy. Make sure that drainage is good and that there are no hidden
areas in the bilges where water can lie. Limber holes should be large and open. For
safety and longer coating life, keep fuel and oil out of the bilges.
An open interior layout is better for ventilation. Do not let clutter build up. See that no
water-absorbent materials (leaves or clothing) are in contact with the hull or interior
joiner work.
Watertight deck or cabin openings and effective ventilators with good drainage (such
as dorade boxes or mushrooms) can make the boat more comfortable when in use and
drier at the dock or mooring. If using a fabric mooring cover, vents are available that
can be sewn or snapped into the cover fabric to provide ventilation as well as weather
All of these factors work together to provide good ventilation. If you have questions
about options, we suggest you consult the books listed in Appendix–Additional
reading, page 77.
Using WEST SYSTEM® Epoxy
8 Using WEST SYSTEM® Epoxy
This section is designed to help you understand and safely handle WEST SYSTEM
epoxy products and to provide the basic techniques used in most repair and building
operations. Refer to the WEST SYSTEM User Manual & Product Guide for more
complete product information.
8.1 Epoxy safety
Epoxies are safe when handled properly. To use WEST SYSTEM epoxies safely, you
must understand their hazards and take precautions to avoid them.
The primary hazard associated with epoxy involves skin contact. WEST SYSTEM Resins may cause moderate skin irritation. WEST SYSTEM Hardeners are corrosive and
may cause severe skin irritation. Resins and hardeners are also sensitizers and may
cause an allergic reaction similar to poison ivy. Susceptibility and the severity of a reaction varies with the individual. Although most people are not sensitive to WEST SYSTEM Resins and Hardeners, the risk of becoming sensitized increases with repeated
contact. For those who become sensitized, the severity of the reaction may increase
with each contact. The hazards associated with resins and hardeners also apply to the
sanding dust from epoxy that has not fully cured. These hazards decrease as resin/hardener mixtures reach full cure. Refer to product labels or Material Safety Data Sheets for
specific product warnings and safety information.
1. Avoid contact with resin, hardeners, mixed epoxy and sanding dust from epoxy that is
not fully cured. Wear protective gloves and clothing whenever you handle WEST SYSTEM Epoxies. Barrier skin creams provide additional protection. If you do get resin,
hardener or mixed epoxy on your skin, remove it as soon as possible. Resin is not water
soluble—use a waterless skin cleanser to remove resin or mixed epoxy from your skin.
Hardener is water soluble—wash with soap and warm water to remove hardener or
sanding dust from your skin. Always wash thoroughly with soap and warm water after
using epoxy. Never use solvents to remove epoxy from your skin.
Stop using the product if you develop a reaction. Resume work only after the symptoms disappear, usually after several days. When you resume work, improve your
safety precautions to prevent exposure to epoxy, its vapors, and sanding dust. If problems persist, discontinue use and consult a physician.
2. Protect your eyes from contact with resin, hardeners, mixed epoxy, and sanding dust
by wearing appropriate eye protection. If contact occurs, immediately flush the eyes
with water under low pressure for 15 minutes. If discomfort persists, seek medical
3. Avoid breathing concentrated vapors and sanding dust. WEST SYSTEM epoxies have
low VOC content, but vapors can build up in unvented spaces. Provide ample ventilation when working with epoxy in confined spaces, such as boat interiors. When adequate ventilation is not possible, wear a NIOSH (National Institute for Occupational
Using WEST SYSTEM® Epoxy
Safety and Health) approved respirator with an organic vapor cartridge. Provide ventilation and wear a dust mask when sanding epoxy, especially uncured epoxy. Breathing
uncured epoxy dust increases your risk of sensitization. Although epoxy cures quickly
to a sandable solid, it may take over two weeks at room temperature, or post-curing, to
cure completely.
4. Avoid ingestion. Wash thoroughly after handling epoxy, especially before eating or
smoking. If epoxy is swallowed, drink large quantities of water—DO NOT induce
vomiting. Because hardeners are corrosive, they can cause additional harm if vomited.
Call a physician immediately. Refer to First Aid procedures on the Material Safety Data
For additional safety information or data, write to: EPOXY SAFETY, Gougeon Brothers, Inc., PO Box 908, Bay City, MI 48707 USA or visit www.westsystem.com.
8.1.1 Cleanup
Contain large spills with sand, clay or other inert absorbent material. Use a scraper to
contain small spills and collect as much material as possible. Follow up with absorbent
towels. Uncontaminated resin or hardener may be reclaimed for use. DO NOT use saw
dust or other fine cellulose materials to absorb hardeners. DO NOT dispose of hardener in trash containing saw dust or other fine cellulose materials—spontaneous
combustion can occur.
Clean resin or mixed epoxy residue with lacquer thinner, acetone or alcohol. Follow
all safety warnings on solvent containers. Clean hardener residue with warm soapy water. Clean 207 Hardener residue with alcohol.
Dispose of resin, hardener and empty containers safely. Puncture a corner of the can
and drain residue into the appropriate new container of resin or hardener. DO NOT
dispose of resin or hardener in a liquid state. Waste resin and hardener can be mixed
and cured (in small quantities) to a non-hazardous inert solid.
Pots of curing epoxy can get hot enough to ignite surrounding combustiI CAUTION!
ble materials and give off hazardous fumes. Place pots of mixed epoxy in a safe and
ventilated area, away from workers and combustible materials. Dispose of the solid
mass only if curing is complete and the mass has cooled. Follow federal, state or local
disposal regulations.
8.2 Epoxy products
This section provides a short description of WEST SYSTEM resin, hardeners and fillers. Refer to the current User Manual & Product Guide for complete information on all
WEST SYSTEM products.
8.2.1 Resin and hardeners
105 Resin—A clear, light-amber, low-viscosity, epoxy resin that can be cured in a wide
temperature range to yield a high-strength, rigid solid which has excellent cohesive
properties and is an outstanding bonding adhesive and moisture vapor barrier. WEST
SYSTEM 105 Resin is formulated for use with four different WEST SYSTEM hardeners. Use the Hardener Selection Guide (Figure 8-1) to select the hardener most suited
for your application.
Using WEST SYSTEM® Epoxy
205 Hardener—Used for general bonding, barrier coating and fabric application. Formulated to cure at lower temperatures and to produce a rapid cure that develops its
physical properties quickly at room temperature. 5:1 mix ratio.
206 Slow Hardener—Used for general bonding, barrier coating and fabric application.
Formulated for a longer working and cure time or to provide adequate working time at
higher temperatures. 5:1 mix ratio.
Note: 205 Fast and 206 Slow Hardener may be blended for intermediate cure times.
Always maintain the proper 5 part resin to 1 part hardener ratio. Do not mix 205 or
206 (5-to-1 ratio) Hardeners with 207 or 209 (3-to-1 ratio) Hardeners.
207 Special Coating Hardener—Formulated specifically for barrier coating and fabric
application where clear finish is desired. 207 contains a UV stabilization additive, but
still requires long term UV protection with paint or varnish. It provides good physical
properties for bonding, but it is more difficult to thicken and less cost effective for this
purpose than 205 or 206 hardener. 207 is a light amber color that will tint wood
slightly darker and warmer, similar to varnish. 3:1 mix ratio.
209 Extra Slow Hardener— Used for general bonding, barrier coating and fabric application in extremely warm and/or humid conditions. Provides approximately twice
the pot life and working time as 206 Slow Hardener and adequate pot life up to 110°F
(43°C). Also used at room temperatures when a long pot life and working time are
required. 3:1 mix ratio.
Hardener Selection Guide
CURE SPEEDS at room temperature*
General bonding, fabric application and barrier coating
General bonding, fabric application and barrier coating
Clear fabric application and
General bonding, fabric application and barrier coating
Room Temp.
100g cupful
thin film
thin film
*Epoxy cures faster in warmer temperatures and in thicker applications—Epoxy cures slower in cooler temperatures and in thinner applications.
Figure 8-1 Select a hardener for its intended use and for the cure speed best suited for your job, in the temperature range you are
working in.
8.2.2 Fillers
Throughout this manual, we will refer to epoxy or resin/hardener mixture, meaning
mixed resin and hardener without fillers added; and thickened mixture or thickened
epoxy, meaning resin/hardener with one of six fillers added.
Fillers are used to thicken the epoxy for specific applications. They are categorized as
either Adhesive Fillers—used for structural bonding or gluing, and gap-filling; or Fairing Fillers—used for cosmetic surface filling. Although each filler has unique handling
and cured characteristics that make it more suitable for some jobs than others (Figure
8-2), for most bonding applications any of the adhesive fillers can be used. And for
most surface filling, either of the fairing fillers can be used. Fillers may also be blended
for intermediate characteristics.
Using WEST SYSTEM® Epoxy
Adhesive fillers
403 Microfibers—For general bonding and gap filling. Epoxy/403 mixtures have superior gap-filling qualities and good strength for most bonding applications while retaining wetting/penetrating capabilities. Works especially well with porous woods.
Cures to an off-white color.
404 High-Density Filler—For hardware fastener bonding and applications that require maximum physical properties and where high-cyclic loads are anticipated. Also
used for gap-filling where maximum strength is necessary. Cures to an off-white color.
405 Filleting Blend—For use in bonding and filleting on naturally finished wood projects. A strong, wood-toned filler that mixes easily and spreads smoothly. Cures to a
brown color and can be used to tint other fillers.
406 Colloidal Silica—For general bonding, gap-filling, high-strength bonds and fillets.
A practical and versatile, smooth-textured filler. It can be used alone or mixed with
other fillers to improve workability and smoothness. Cures to an off-white color.
Fairing fillers
407 Low-Density Filler—A blended microballoon-based filler used to make a fairing
compound that is easy to sand or carve while still being reasonably strong on a
strength-to-weight basis. Cures to a reddish-brown color.
410 Microlight™—A very low-density filler for creating a light, easily-worked fairing
compound. 410 spreads smoothly and sands very easily when cured. Not recommended under dark colored paint or on other surfaces subject to high temperatures.
Cures to a light tan color.
See Appendix —Estimating Guides for WEST SYSTEM products, for additional filler selection information.
Filler Selection Guide
Resin/Hardener mixture
thickened with a Filler
Use description—Desired characteristics
Highest density
Highest strength
Lowest density
Easiest sanding
Filleting Blend
Bonding with Fillets—Increase joint bonding area and create a structural brace between parts—Smoothness/strength
Laminating—Bond layers of wood strips, veneers, planks, sheets and cores—Gap filling/strength
Bonding Hardware—Increased fastener interface and hardware load capability—Maximum strength
General Bonding—Join parts with epoxy
thickened to create a structural gap
filler—Strength/gap filling
Fairing—Fill low areas and voids with an easily shaped and sanded surface filler/fairing
compound—Sandability/gap filling
High-density Colloidal Silica
Figure 8-2 Selecting Fillers—As a rule, use higher-density fillers when bonding higher-density materials such as hardwoods and metals. Any of the adhesive fillers are suitable for most bonding situations. Your choice of a filler for general use may be based on the handling characteristics you prefer. Fillers may also be blended to create mixtures with intermediate characteristics.
Using WEST SYSTEM® Epoxy
8.3 Handling epoxy
This section explains the fundamentals of epoxy curing and the steps for proper dispensing, mixing, and adding fillers to assure that every batch of epoxy cures to a useful
high-strength solid.
8.3.1 Understanding epoxy's cure stages
Epoxy Temperature
Mixing epoxy resin and hardener begins a chemical reaction that transforms the combined liquid ingredients to a solid. The time it takes for this transformation is the cure
time. As it cures the epoxy passes from the liquid state, through a gel state, before it
reaches a solid state (Figure 8-3).
Open time
Initial cure
Tack free
Figure 8-3 As it cures, mixed epoxy passes from a liquid state,
through a gel state, to a solid state.
Cure time is shorter when the epoxy
is warmer. Cure time is longer when
the epoxy is cooler.
Minimum Recommended Temperature
Cure time after mixing
1. Liquid—Open time
Open time (also working time or wet lay-up time) is the portion of the cure time, after
mixing, that the resin/hardener mixture remains a liquid and is workable and suitable
for application. All assembly and clamping should take place during the open time to
assure a dependable bond.
2. Gel—Initial cure
The mixture passes into an initial cure phase (also called the green stage) when it begins
to gel, or "kick off". The epoxy is no longer workable and will no longer feel tacky. During this stage it progresses from a soft gel consistency to the firmness of hard rubber.
You will be able to dent it with your thumb nail.
The mixture will become tack free about midway through the initial cure phase. While
it is still tacky, a new application of epoxy will still chemically link with it, so the surface
may still be bonded to or recoated without special preparation. However, this ability
diminishes as the mixture approaches the final cure phase.
3. Solid—Final cure
The epoxy mixture has cured to a solid state and can be dry sanded and shaped. You
should not be able to dent it with your thumbnail. At this point the epoxy has reached
most of its ultimate strength, so clamps can be removed. It will continue to cure over
the next several days at room temperature.
A new application of epoxy will no longer chemically link to it, so the surface of the epoxy must be properly prepared and sanded before recoating to achieve a good mechanical, secondary bond. See Surface Preparation 8.4.1.
8.3.2 Understanding and controlling cure time
Open time and cure time govern much of the activity of building and repairing with epoxy. Open time dictates the time available for mixing, application, smoothing, shaping,
assembly and clamping. Cure time dictates how long you must wait before removing
Using WEST SYSTEM® Epoxy
clamps, or before you can sand or go on to the next step in the project. Two factors determine an epoxy mixture’s open time and overall cure time—hardener cure speed and epoxy temperature.
Hardener speed
Each hardener has an ideal temperature cure range (Figure 8-1). At any given temperature, each resin/hardener combination will go through the same cure stages, but at different rates. Select the hardener that gives you adequate working time for the job you
are doing at the temperature and conditions you are working under. The product guide
and container labels describe hardener pot lives and cure times.
Pot life is a term used to compare the cure speeds of different hardeners. It is the
amount of time a specific mass of mixed resin and hardener remains a liquid at a specific temperature. (A 100g-mass mixture in a standard container, at 72°F). Because pot
life is a measure of the cure speed of a specific contained mass (volume) of epoxy rather
than a thin film, a hardener's pot life is much shorter than its open time.
Epoxy temperature
The warmer the temperature of curing epoxy, the faster it cures (Figure 8-3). Curing
epoxy's temperature is determined by the ambient temperature plus the exothermic
heat generated by its cure.
Ambient temperature is the temperature of the air or material in contact with the epoxy. Air temperature is most often the ambient temperature unless the epoxy is applied
to a surface with a different temperature. Generally, epoxy cures faster when the air
temperature is warmer.
Exothermic heat is produced by the chemical reaction that cures epoxy. The amount of
heat produced depends on the thickness or exposed surface area of mixed epoxy. In a
thicker mass, more heat is retained, causing a faster reaction and more heat. The mixing container shape and mixed quantity have a great affect on this exothermic reaction.
A contained mass of curing epoxy (8 fl. oz. or more) in a plastic mixing cup can quickly
generate enough heat to melt the cup and burn your skin. However, if the same quantity is spread into a thin layer, exothermic heat is dissipated, and the epoxy's cure time
is determined by the ambient temperature. The thinner the layer of curing epoxy, the
less it is affected by exothermic heat, and the slower it cures.
Controlling cure time
In warm conditions use a slower hardener, if possible. Mix smaller batches that can be
used up quickly, or quickly pour the epoxy mixture into a container with greater surface area (a roller pan, for example), thereby allowing exothermic heat to dissipate and
extending open time. The sooner the mixture is transferred or applied (after thorough
mixing), the more of the mixture’s useful open time will be available for coating, lay-up
or assembly.
In cool conditions use a faster hardener or use supplemental heat to raise the epoxy
temperature above the hardeners minimum recommended application temperature.
Use a hot air gun, heat lamp or other heat source to warm the resin and hardener before
mixing or after the epoxy is applied. At room temperature, supplemental heat is useful
when a quicker cure is desired. NOTE! Unvented kerosene or propane heaters can inhibit the cure of epoxy and contaminate epoxy surfaces with unburned hydrocarbons.
Heating epoxy that has not gelled will lower its viscosity, allowing the epI CAUTION!
oxy to run or sag more easily on vertical surfaces. In addition, heating epoxy applied to
a porous substrate (soft wood or low density core material) may cause the substrate to
“out-gas” and form bubbles in the epoxy coating. To avoid outgassing, wait until the
epoxy coating has gelled before warming it. Never heat mixed epoxy in a liquid state
over 120°F (49°C).
Using WEST SYSTEM® Epoxy
Regardless of what steps are taken to control the cure time, thorough planning of the
application and assembly will allow you to make maximum use of the epoxy mixture's
open time and cure time.
8.3.3 Dispensing and mixing
Careful measuring of epoxy resin and hardener and thorough mixing are essential for a
proper cure. Whether the resin/hardener mixture is applied as a coating or modified
with fillers or additives, observing the following procedures will assure a controlled
and thorough chemical transition to a high-strength epoxy solid.
Dispense the proper proportions of resin and hardener into a clean plastic, metal or
wax-free paper container. Don’t use glass or foam containers because of the potential
danger from exothermic heat buildup. DO NOT attempt to alter the cure time by altering the ratio. An accurate ratio is essential for a proper cure and full development of
physical properties.
Dispensing with Mini pumps
Most problems related to curing of the epoxy can be traced to the wrong ratio of resin
and hardener. To simplify metering, we recommend using calibrated WEST SYSTEM
Mini Pumps to dispense the resin and hardener. 301 Mini Pumps and 303 Special Ratio Mini Pumps are calibrated to deliver the proper working ratio of resin to hardener.
Pump one full pump stroke of resin for each one full pump stroke of hardener. Depress
each pump head fully and allow the head to come completely back to the top before beginning the next stroke (Figure 8-4). Partial strokes will give the wrong ratio. Read the
pump instructions before using pumps.
Scrape corners
Figure 8-4 Dispense the proper proportions of resin
and hardener.
Figure 8-5 Stir resin and hardener together thoroughly, at least one minute—longer in cooler temperatures.
Before you use the first mixture on a project, verify the proper ratio according to the instructions that come with the pumps. Recheck the ratio anytime you experience problems with curing.
Dispensing without Mini Pumps—Weight/volume measure
To measure 105 Resin and 205 or 206 Hardener by weight or volume, combine 5 parts
resin with 1 part hardener. To measure 105 Resin and 207 or 209 Hardener by volume, combine 3 parts resin with 1 part hardener (by weight, 3.5 parts resin–1 part
First time users—Begin with a small test batch to get the feel for the mixing and curing process before applying the mixture to your project. This will demonstrate the
hardener's open time for the temperature you are working in and assure you that the
resin/hardener ratio is metered properly. Mix small batches until you are confident of
the mixture's handling characteristics.
Using WEST SYSTEM® Epoxy
Stir the two ingredients together thoroughly, at least one minute—longer in cooler
temperatures (Figure 8-5). To assure thorough mixing, scrape the sides and bottom of
the pot as you mix. Use the flat end of the mixing stick to reach the inside corner of the
pot. If you are using a power mixer, occasionally scrape the sides and corners of the
mixing pot while mixing.
If you are going to be using the mixture for coating, quickly pour it into a roller pan to
extend the open time.
Curing epoxy generates heat. Do not fill or cast layers of epoxy thicker
than ½"—thinner if enclosed by foam or other insulated material. Several inches of
mixed epoxy in a plastic mixing cup will generate enough heat to melt the cup if left to
stand for its full pot life. For this reason, do not use foam or glass mixing containers. If a
pot of mixed epoxy begins to exotherm (heat up), quickly move it outdoors. Avoid
breathing the fumes. Do not dispose of the mixture until the reaction is complete and
has cooled.
8.3.4 Adding fillers and additives
After selecting an appropriate filler for your job (Section 8.2.2), use it to thicken the epoxy mixture to the desired consistency. The thickness of a mixture required for a particular job is controlled by the amount of filler added. There is no strict formula or
measuring involved—use your eye to judge what consistency will work best. Figure 8-6
gives you a general guide to the differences between unthickened epoxy and the three
consistencies referred to in this manual.
Figure 8-6 Epoxy can
be thickened to the exact consistency needed
for a particular job. The
procedures in this manual refer to four common consistencies;
syrup, catsup, mayonnaise and peanut butter.
Unthickened mixture.
Slightly thickened.
Moderately thickened.
Maximum thickness.
Drips off vertical surfaces.
Sags down vertical surfaces.
Clings to vertical surfaces–peaks fall over.
Clings to vertical surfaces–peaks stand up.
Coating, “wetting-out”
before bonding, applying fiberglass, graphite
and other fabrics.
Laminating/bonding flat
panels with large surface areas, injecting
with a syringe.
General bonding, filleting, hardware bonding.
Gap filling, filleting, fairing, bonding uneven
Always add fillers in a two-step process:
1. Mix the desired quantity of resin and hardener thoroughly before adding fillers. Begin
with a small batch—allow room for the filler.
2. Blend in small handfuls or scoops of the appropriate filler until the desired consistency
is reached (Figure 8-7).
For maximum strength, add only enough filler to completely bridge gaps between surfaces without sagging or running out of the joint or gap. A small amount should
squeeze out of joints when clamped. For thick mixtures, don't fill the mixing cup more
than 1/3 full of epoxy before adding filler. When making fairing compounds, stir in as
much 407 or 410 as you can blend in smoothly—for easy sanding, the thicker the
better. Be sure all of the filler is thoroughly blended before the mixture is applied.
Using WEST SYSTEM® Epoxy
Figure 8-7 Blend in
small handfuls or scoops
of the appropriate filler
until the desired consistency is reached.
Additives are used to give epoxy additional physical properties when used as a coating.
Although additives are blended with mixed epoxy in the same two-step process as fillers, they are not designed to thicken the epoxy. Follow the mixing instructions on the
individual additive containers.
8.3.5 Removing epoxy
Removing uncured or non-curing epoxy. Removed uncured epoxy as you would
spilled resin. Scrape as much material as you can from the surface using a stiff metal or
plastic scraper—warm the epoxy to lower its viscosity. Clean the residue with lacquer
thinner, acetone, or alcohol. Follow safety warnings on solvents and provide adequate
ventilation. After recoating wood surfaces with epoxy, it's a good idea to brush the wet
epoxy (in the direction of the grain) with a wire brush to improve adhesion. Allow
solvents to dry before recoating.
Removing fiberglass cloth applied with epoxy. Use a heat gun to heat and soften the
epoxy. Start in a small area near a corner or an edge. Apply heat until you can slip a
putty knife or chisel under the cloth (about 200°F). Grab the edge with a pair of pliers
and pull up on the cloth while heating just ahead of the separation. On large areas, use a
utility knife to score the glass and remove in narrower strips. Resulting surface texture
may be coated or remaining epoxy may be removed as follows.
Removing cured epoxy coating. Use a heat gun to soften the epoxy (200°F). Heat a
small area and use a paint or cabinet scraper to remove the bulk of the coating. Sand the
surface to remove the remaining material. Provide ventilation when heating epoxy.
8.4 Basic techniques
The following basic techniques are common to most repair or building projects, regardless of the type of structure or material you are working with.
8.4.1 Surface preparation
Whether you are bonding, fairing or applying fabrics, the success of the application depends not only on the strength of the epoxy, but also on how well the epoxy adheres to
the surface to which it is being applied. Unless you are bonding to partially cured epoxy, the strength of the bond relies on the epoxy’s ability to mechanically “key” into
the surface. That is why the following three steps of surface preparation are a critical
part of any secondary bonding operation.
For good adhesion, bonding surfaces should be:
Using WEST SYSTEM® Epoxy
1. Clean
Bonding surfaces must be free of any contaminants such as grease, oil, wax or mold release. Clean contaminated surfaces with lacquer thinner, acetone or other appropriate
solvent. Wipe the surface with paper towels before the solvent dries. Clean surfaces before sanding to avoid sanding the contaminant into the surface. Follow all safety precautions when working with solvents.
2. Dry
All bonding surfaces must be as dry as possible for good adhesion. If necessary, accelerate drying by warming the bonding surface with hot air guns, hair dryers or heat lamps.
Use fans to move the air in confined or enclosed spaces. Watch for condensation when
working outdoors or whenever the temperature of the work environment changes.
3. Sanded
Sand smooth non-porous surfaces—thoroughly abrade the surface. For most surfaces,
80-grit aluminum oxide paper will provide a good texture for the epoxy to “key” into.
Be sure the surface to be bonded is solid. Remove any flaking, chalking, blistering, or
old coating before sanding. Remove all dust after sanding.
Special preparation for various materials
Cured epoxy—Amine blush can appear as a wax-like film on cured epoxy surfaces. It is
a byproduct of the curing process and may be more noticeable in cool, moist conditions. Amine blush can clog sandpaper and inhibit subsequent bonding, but it can easily
be removed. It’s a good idea to assume it has formed on any cured epoxy surface.
To remove the blush, wash the surface with clean water (not solvent) and an abrasive
pad, such as Scotch-brite™ 7447 General Purpose Hand Pads. Dry the surface with paper towels to remove the dissolved blush before it dries on the surface. Sand any remaining glossy areas with 80-grit sandpaper. Wet-sanding will also remove the amine
blush. If a release fabric is applied over the surface of fresh epoxy, all amine blush will
be removed when the release fabric is peeled from the cured epoxy and no additional
sanding is required.
Epoxy surfaces that have not fully cured may be bonded to or coated with epoxy without washing or sanding. Before applying coatings other than epoxy (paints, bottom
paints, varnishes, gelcoats, etc.), allow epoxy surfaces to cure fully, then wash and
Hardwoods—Sand with 80-grit paper. (Sand white oak with 60-grit.)
Teak/oily woods—Wipe with acetone 15 minutes before coating. The solvent dries the
oil at the surface and allows epoxy to penetrate. Be sure the solvent has evaporated before coating.
Porous woods—No special preparation needed. If surface is burnished, possibly by
dull planer blades, sand with 80-grit paper to open pores.
Using WEST SYSTEM® Epoxy
Steel, lead—Remove contamination, sand or grind to bright metal, coat with epoxy
then sand fresh epoxy into surface. Recoat or bond after first coat gels.
Aluminum—Sand and prepare with 860 Aluminum Etch Kit.
Polyester (fiberglass)—Clean contamination with a silicone and wax remover such as
DuPont Prep-Sol™ 3919S. Sand with 80-grit paper to a dull finish.
Plastic—Adhesion varies. If a plastic is impervious to solvents such as acetone, epoxy
generally will not bond to it. Soft, flexible plastics such as polyethylene, polypropylene, nylon, Plexiglas and polycarbonate fall into this category.
Hard, rigid plastics such as PVC, ABS and styrene provide better adhesion with good
surface preparation and adequate bonding area. After sanding, flame oxidizing (by
quickly passing propane torch over the surface without melting the plastic) can improve bonding in some plastics. Its a good idea to conduct an adhesion test on a plastic
that you are uncertain about.
8.4.2 Bonding (gluing)
This section refers to two types of structural bonding. Two-step bonding is the
preferred method for most situations because it promotes maximum epoxy
penetration into the bonding surface and prevents resin-starved joints. Single-step
bonding can be used when joints have minimal loads and excess absorption into porous
surfaces is not a problem. In both cases, epoxy bonds best when it is worked into the
surface with a roller or brush
§ Wet out— To
Precoat a joint’s bonding
surfaces with unthickened
epoxy for maximum penetration and adhesion before an additional coat of
thickened epoxy is applied.
Especially useful and recommended on porous surfaces.
NOTE: Joint strength—the ability to adequately transfer a load from one part to
a n o t h e r — d e p e n d s o n t h e co m b i n e d ef f e c t s o f t h r e e f a c t o r s . G L U E
STRENGTH—Careful metering and thorough mixing will assure the epoxy mixture
cures to full strength. SURFACE PREPARATION—For the best adhesion and load
transfer the surface must be properly prepared. JOINT AREA—The bonding area, or
adhesive area, of the joint must be adequate for the load on the joint. Increased overlap,
scarf joints, fillets and reinforcing fibers across the joint can be used to increase
bonding area.
Before mixing epoxy, check all parts to be bonded for proper fit and surface preparation (Surface preparation—8.4.1), gather all the clamps and tools necessary for the operation, and cover any areas that need protection from spills.
Two-step bonding
1. Wet-out bonding surfaces—Apply a neat resin/hardener mixture (without fillers) to
the surfaces to be joined (Figure 8-8). Wet out small or tight areas with a disposable
brush. Wet out larger areas with a foam roller or by spreading the resin/hardener mixture evenly over the surface with a plastic spreader. You may proceed with step two immediately or any time before the wet-out coat becomes tack free.
Figure 8-8 Wet out the bonding surfaces by applying
resin/hardener mixture with a brush or roller.
Figure 8-9 Apply thickened epoxy to one of the bonding surfaces.
Using WEST SYSTEM® Epoxy
2. Apply thickened epoxy to one bonding surface. Modify the resin/hardener mixture by
stirring in the appropriate filler until it becomes thick enough to bridge any gaps
between the mating surfaces and to prevent “resin-starved” joints. Apply enough of the
mixture to one of the surfaces, so that a small amount will squeeze out when the
surfaces are joined together with a force equivalent to a firm hand grip (Figure 8-9).
Thickened epoxy can be applied immediately over the wet-out surface or any time
before the wet-out is no longer tacky. For most small bonding operations, add the filler
to the resin/hardener mixture remaining in the batch that was used for the wet-out.
Mix enough resin/hardener for both steps. Add the filler quickly after the surface is wet
out and allow for a shorter working life of the mixture.
3. Clamp components. Attach clamps as necessary to hold the components in place. Use
just enough clamping pressure to squeeze a small amount of the epoxy mixture from
the joint, indicating that the epoxy is making good contact with both mating surfaces
(Figure 8-10). Avoid using too much clamping pressure, which can squeeze all of the
epoxy mixture out of the joint.
Figure 8-10 Clamp components in place before the
epoxy gels.
Figure 8-11 Remove or shape excess epoxy that
squeezes out of the joint.
4. Remove or shape excess adhesive that squeezes out of the joint as soon as the joint is
secured with clamps. A wooden mixing stick with one end sanded to a chisel edge is an
ideal tool for removing the excess (Figure 8-11).
Single-step bonding
Single-step bonding is applying the thickened epoxy directly to both bonding surfaces
without first wetting out the surfaces with neat resin/hardener. We recommend that
you thicken the epoxy no more than is necessary to bridge gaps in the joint (the thinner
the mixture, the more it can penetrate the surface) and that you do not use this method
for highly-loaded joints or for bonding end grain or other porous surfaces.
The term “laminating” refers to the process of bonding numbers of relatively thin
layers, like plywood, veneers, fabrics or core material to create a composite. A
composite may be any number of layers of the same material or combinations of
different materials. Methods of epoxy application and clamping will differ depending
on what you are laminating.
Because of large surface areas and limitations of wet lay-up time, roller application is
the most common method for applying epoxy. A faster method for large surfaces is to
simply pour the resin/hardener mixture onto the middle of the panel and spread the
mixture evenly over the surface with a plastic spreader. Apply thickened mixtures with
an 809 Notched Spreader.
Using staples or screws is the most common method of clamping when you laminate a
solid material to a solid substrate. An even distribution of weights will work when you
are laminating a solid material to a base that will not hold staples or screws, such as a
foam or honeycomb core material.
Using WEST SYSTEM® Epoxy
Vacuum bagging is the ideal clamping method for laminating a wide range of materials.
Through the use of a vacuum pump and plastic sheeting, the atmosphere is used to
apply perfectly even clamping pressure over all areas of a panel regardless of the size,
shape or number of layers. For detail information on vacuum bagging, refer to 002-150
Vacuum Bagging Techniques.
8.4.3 Bonding with fillets
A fillet (fil’it) is a cove-shaped application of thickened epoxy that bridges an inside
corner joint. It is excellent for bonding parts because it increases the surface area of the
bond and serves as a structural brace. All joints that will be covered with fiberglass cloth
will require a fillet to support the cloth at the inside corner of the joint.
The procedure for bonding with fillets is the same as normal bonding except that
instead of removing the squeezed-out thickened epoxy after the components are
clamped in position, you shape it into a fillet. For larger fillets, add thickened mixture
to the joint as soon as the bonding operation is complete, before the bonding mixture
becomes tack free, or any time after the final cure and sanding of exposed epoxy in the
fillet area.
1. Bond parts as described in 8.4.2 Bonding.
2. Shape and smooth the squeezed-out thick epoxy into a fillet by drawing a rounded
filleting tool (mixing stick) along the joint, dragging excess material ahead of the tool
and leaving a smooth cove-shaped fillet bordered on each side by a clean margin. Some
excess filleting material will remain outside of the margin (Figure 8-12). Use the excess
material to re-fill any voids. Smooth the fillet until you are satisfied with its
appearance. A mixing stick will leave a fillet with about a 3 8" radius. For larger fillets, an
808 Flexible Spreader, cut to shape or bent to the desired radius, works well.
Apply additional thickened epoxy to fill voids or make larger fillets. Apply the mixture
along the joint line with the rounded mixing stick, using enough mixture to create the
desired size of fillet. For longer or multiple fillets, empty caulking gun cartridges or
disposable cake decorating bags can be used. Cut the plastic tip to lay a bead of
thickened epoxy large enough for the desired fillet size. Heavy duty, sealable food
storage bags with one corner cut off may also be used.
Figure 8-12 Shape and smooth the fillet with a
rounded filleting tool.
Figure 8-13 Clean up the excess epoxy outside of the
fillet margin.
3. Clean up the remaining excess material outside of the margin by using a sharpened
mixing stick or a putty knife (Figure 8-13). Fiberglass cloth or tape may be applied over
the fillet area before the fillet has cured (or after the fillet is cured and sanded).
4. Sand smooth with 80-grit sandpaper after the fillet has fully cured. Wipe the surface
clean of any dust and apply several coats of resin/hardener over the entire fillet area
before final finishing.
Using WEST SYSTEM® Epoxy
8.4.4 Fairing
Fairing refers to the filling and shaping of low areas so they blend with the surrounding
surfaces and appear “fair” to the eye and touch. After major structural assembly has
been completed, final fairing can be easily accomplished with WEST SYSTEM epoxy
and 407 or 410 low-density fillers.
1. Prepare the surface as you would for bonding (Section 8.4.1). Sand smooth any bumps
or ridges on the surface and remove all dust from the area to be faired.
2. Wet out porous surfaces with unthickened epoxy (Figure 8-14).
3. Mix resin/hardener and 407 Low-Density or 410 Microlight™ filler to a peanut butter
Figure 8-14 Wet out porous surfaces before applying
thickened fairing compound.
Figure 8-15 Trowel the thickened epoxy fairing compound into the voids and depressions with a plastic
4. Trowel on the thickened epoxy mixture with a plastic spreader, working it into all
voids and depressions. Smooth the mixture to the desired shape, leaving the mixture
slightly higher than the surrounding area (Figure 8-15). Remove any excess thickened
epoxy before it cures. If the voids you are filling are over ½" deep, apply the mixture in
several applications or use 206 Slow Hardener or 209 Extra Slow Hardener, depending on ambient temperature.
5. Allow the final thickened epoxy application to cure thoroughly.
6. Sand the fairing material to blend with the surrounding contour (Figure 8-16). Begin
with 50-grit sandpaper if you have a lot of fairing material to remove. Use 80-grit paper
on the appropriate sanding block when you are close to the final contour.
CAUTION! Don’t forget your dust mask. Remove the sanding dust and fill any remaining voids following the same procedure.
Figure 8-16 Sand the fairing material to blend with
the surrounding contour.
7. Apply several coats of resin/hardener to the area with a disposable brush or roller after
you are satisfied with the fairness. Allow the final coat to cure thoroughly before final
sanding and finishing.
Using WEST SYSTEM® Epoxy
8.4.5 Applying woven cloth and tape
Fiberglass cloth is applied to surfaces to provide reinforcement and/or abrasion resistance, or in the case of Douglas Fir plywood, to prevent grain checking. It is usually applied after fairing and shaping are completed, and before the final coating operation. It
is also applied in multiple layers (laminated) and in combination with other materials
to build composite parts.
Fiberglass cloth may be applied to surfaces by either of two methods. The “dry”
method refers to applying the cloth over a dry surface. The “wet” method refers to applying the cloth to an epoxy-coated surface often after the wet-out coat becomes tacky,
which helps it cling to vertical or overhead surfaces. Since this method makes it more
difficult to position the cloth, the dry method is the preferred method especially with
thinner cloth.
Dry method
1. Prepare the surface as you would for bonding (Section 8.4.1).
2. Position the cloth over the surface and cut it several inches larger on all sides. If the surface area you are covering is larger than the cloth size, allow multiple pieces to overlap
by approximately two inches. On sloped or vertical surfaces, hold the cloth in place
with masking or duct tape, or with staples.
3. Mix a small quantity of epoxy (three or four pumps each of resin and hardener).
4. Pour a small pool of resin/hardener near the center of the cloth.
5. Spread the epoxy over the cloth surface with a plastic spreader, working the epoxy
gently from the pool into the dry areas (Figure 8-17). Use a foam roller or brush to wet
out fabric on vertical surfaces. Properly wet out fabric is transparent. White areas indicate dry fabric. If you are applying the cloth over a porous surface, be sure to leave
enough epoxy to be absorbed by both the cloth and the surface below it. Try to limit the
amount of squeegeeing you do. The more you “work” the wet surface, the more minute air bubbles are placed in suspension in the epoxy. This is especially important if you
plan to use a clear finish (see note page 70). You may use a roller or brush to apply epoxy to horizontal as well as vertical surfaces.
Figure 8-17 Spread the epoxy from the center of the
fabric toward the edges with a plastic spreader.
Figure 8-18 Squeegee away excess epoxy before the
first batch begins to gel.
Smooth wrinkles and position the cloth as you work your way to the edges. Check for
dry areas (especially over porous surfaces) and re-wet them as necessary before proceeding to the next step. If you have to cut a pleat or notch in the cloth to lay it flat on a
compound curve or corner, make the cut with a pair of sharp scissors and overlap the
edges for now.
Using WEST SYSTEM® Epoxy
NOTE: For clear wood finishes, an alternative wet out method is to lay the epoxy onto
the fabric with a short-bristled brush. Dip the brush in the epoxy and lay the epoxy on
the surface in a light even stroke. Don’t force the epoxy into the cloth,which may trap
air in the fabric and show through the clear finish. Apply enough epoxy to saturate the
fabric and the wood below. After several minutes, lay on additional epoxy to dry
(white) areas.
7. Squeegee away excess epoxy before the first batch begins to gel (Figure 8-18). Drag the
spreader over the fabric, using even-pressured, overlapping strokes. Use enough pressure to remove excess epoxy that would allow the cloth to float off the surface, but not
enough pressure to create dry spots. Excess epoxy appears as a shiny area, while a
properly wet-out surface appears evenly transparent, with a smooth, cloth texture.
Later coats of epoxy will fill the weave of the cloth.
8. Trim the excess and overlapped cloth after the epoxy has reached its initial cure. The
cloth will cut easily with a sharp utility knife (Figure 8-19). Trim overlapped cloth, if
desired, as follows:
Figure 8-19 Trim excess
cloth when the epoxy
reaches its initial cure
phase. The wet-out cloth
will be dry but flexible and
will trim easily with a sharp
utility knife.
a) Place a metal straightedge on top of and midway between the two overlapped edges.
b) Cut through both layers of cloth with a sharp utility knife (Figure 8-20).
c) Remove the topmost trimming and then lift the opposite cut edge to remove the
overlapped trimming (Figure 8-21). d) Re-wet the underside of the raised edge with epoxy and smooth into place.
Figure 8-20 Trim overlapping fabric using a metal
straightedge and a sharp utility knife, for a flush butt
Figure 8-21 Remove the topmost trimming. Then lift
the opposite cut edge to remove the overlapped trimming.
The result should be a near perfect butt joint, eliminating double cloth thickness. A
lapped joint is stronger than a butt joint, so if appearance is not important, you may
want to leave the overlap and fair in the unevenness after coating.
9. Coat the surface to fill the weave before the wet-out reaches its final cure stage (Figure
8-22). Follow the procedures for epoxy barrier coating under Section 7.2. It will take
Using WEST SYSTEM® Epoxy
Figure 8-22 Apply
the first coat of unthickened epoxy to
fill the weave of the
cloth before the wetout coat reaches its
final cure phase.
two or three coats to completely fill the weave of the cloth and to allow for a final sanding that will not affect the cloth.
Wet method
An alternative is to apply the fabric or tape to a surface coated with wet epoxy. As mentioned, this is not the preferred method, especially with large pieces of cloth, because
of the difficulty removing wrinkles or adjusting the position of the cloth as it is being
wet out. However, you may come across situations when this method may be useful or
1. Prepare the surface (Section 8.4.1).
2. Pre-fit and trim the cloth to size. Roll the cloth neatly so that it may be conveniently
rolled back into position later.
3. Roll a heavy coat of epoxy on the surface.
4. Unroll the glass cloth over the wet epoxy and position it. Surface tension will hold most
cloth in position. If you are applying the cloth vertically or overhead, you may want to
wait until the epoxy becomes tacky. Work out wrinkles by lifting the edge of the cloth
and smoothing from the center with your gloved hand or a spreader.
5. Apply a second coat of epoxy with a foam roller. Apply enough epoxy to thoroughly
wet out the cloth.
6. Remove the excess epoxy with a spreader, using long overlapping strokes. The cloth
should appear consistently transparent with a smooth cloth texture.
7. Follow steps 7, 8 and 9 under the dry method to finish the procedure.
Any remaining irregularities or transitions between cloth and substrate can be faired by
using an epoxy/filler fairing compound if the surface is to be painted. Any additional
fairing done after the final coating should receive several additional coats over the
faired area.
Note: A third alternative, a variation of both methods, is to apply the fabric after a wet
out coat has reached an initial cure. Follow the first three steps of the Wet Method, but
wait until the epoxy cures dry to the touch before positioning the fabric and continuing
with Step 3 of the Dry Method. Apply the fabric before the first coat reaches its final
cure phase.
Refer to Section 7, Protecting and Maintaining Wooden Boats for procedures on barrier coating and applying finish coatings.
WEST SYSTEM product estimating guides
WEST SYSTEM product estimating guides
Group size quantities and coating coverage
WEST SYSTEM epoxy resin and hardeners are packaged in three “Group Sizes.” For each container size of resin, there is a corresponding sized container of hardener and a corresponding mini
pump size. When purchasing resin, hardener and mini pumps, be sure all containers are labeled
with the same Group Size letter (A, B or C).
1 qt (.94 L)
.98 gal (3.74 L)
4.35 gal (16.47 L)
Saturation Coat
Porous Surfaces
Buildup Coats
Non-Porous Surfaces
205-A or 206-A
.43 pt (.20 L)
1.2 qt. (1.15 L)
90–105 sq. ft.
120–135 sq. ft.
(11–12.5 m2)
207-A or 209-A
.66 pt (.31 L)
1.3 qt.
(1.26 L)
90–105 sq. ft.
(9–10 m2)
120–135 sq. ft.
11–13 m2)
205-B or 206-B
.86 qt (.81 L)
1.2 gal. (4.55 L)
350–405 sq. ft.
(32–37 m2)
462–520 sq. ft.
(43–48 m2)
207-B or 209-B
1.32 qt (1.24 L)
1.3 gal. (4.98 L)
370–430 sq. ft.
(35–40 m2)
490–550 sq. ft.
(45–50 m2)
205-C or 206-C
.94 gal (3.58 L)
5.29 gal. (20 L)
1530–1785 sq. ft.
(142–165 m2)
2040–2300 sq. ft.
(190–213 m2)
207-C or 209-C
1.45 gal (5.49 L)
5.8 gal. (21.9 L)
1675–1955 sq. ft.
(155–180 m2)
2235–2520 sq. ft.
(207–233 m2)
Fiberglass thickness per layer
Filler/epoxy proportion guide
Fabric weight
4 oz.
6 oz.
9 oz.
12 oz. 15 oz. 22 oz.
Approximate mixed epoxy required to produce a catsup, mayonnaise or peanut butter consistency for
the various sized filler products at 72°F. Mixtures will
be thinner at higher temperatures.
Single layer
Quantity of mixed epoxy required for
Package size
6.0 oz
20.0 oz
20.0 lb
3.8 qt
3.2 gal
48.0 gal
2.5 qt
2.0 gal
32.0 gal
1.0 qt
.9 gal
15.3 gal
15.2 oz
45.6 oz
30.0 lb
1.2 qt
3.6 qt
9.4 gal
.9 qt
2.8 qt
7.4 gal
.7 qt
2.0 qt
5.3 gal
8.0 oz
.9 qt
.7 qt
.6 qt
1.7 oz
5.5 oz
10.0 lb
1.3 qt
1.1 gal
27.0 gal
.9 qt
3.0 qt
16.0 gal
.5 qt
1.7 qt
6.0 gal
4.0 oz
12.0 oz
14.0 lb
.5 qt
1.7 qt
6.0 gal
.4 qt
1.3 qt
4.8 gal
.3 qt
1.0 qt
3.7 gal
2.0 oz
5.0 oz
4.0 lb
1.2 qt
3.0 qt
8.9 gal
.9 qt
2.4 qt
7.2 gal
.7 qt
1.8 qt
5.6 gal
Epoxy shelf life
"Peanut butter”
If the containers are kept
sealed when not in use
WEST SYSTEM resin and
hardeners should remain
usable for many years. Over
time, 105 Resin will thicken
slightly and will therefore require extra care when mixing. Hardeners may darken
with age, but physical properties are not affected by
color. Mini Pumps may be
left in containers during
storage. It is a good idea, after a long storage to verify
the metering accuracy of the
pumps and mix a test batch
to assure proper curing before applying epoxy to your
Problem solving guide
Problem solving guide
This guide is designed to help identify and prevent potential problems associated with using epoxy. If the solutions
described here do not resolve the problem, call the Gougeon technical staff.
The epoxy mixture has
not cured after the recommended cure time
has passed.
Bond failure.
Off ratio-Too much or too
little hardener will affect
the cure time and thoroughness of the cure.
1. Remove epoxy. Do not apply additional material
over non-curing epoxy. See 8.3.5 Removing epoxy.
2. Check correct number of pump strokes-use equal
strokes of resin and hardener. DO NOT add extra
hardener for faster cure!
3. Check pump ratio (see pump instructions).
4. Check for correct pump (5:1 or 3:1 ratio) and
pump group size (Group B resin and Group B hardener).
Low temperature- Epoxy
mixtures cure slower at
low temperatures.
1. Allow extra curing time in cool weather.
2. Apply heat to maintain the chemical reaction and
speed the cure.
3. Use a faster hardener, designed to cure at lower
Insufficient mixing.
1. Remove epoxy. Do not apply additional material
over non-curing epoxy. See 8.3.5 Removing epoxy.
2. Mix resin and hardener together thoroughly to
avoid resin rich and hardener rich areas.
3. Add fillers or additives after resin and hardener
have been thoroughly mixed.
Incorrect products.
1. Remove epoxy. Do not apply additional material
over non-curing epoxy. See 8.3.5 Removing epoxy.
2. Check for proper resin and hardener. Resin will
not cure properly with other brands of hardener or
with polyester catalysts.
Insufficient cure.
See above.
Resin starved joint-epoxy
has wicked into porous
surfaces leaving a void in
the joint.
Wet out bonding surfaces before applying thickened
epoxy. Re-wet very porous surfaces like end grain.
Contaminated bonding
Clean and sand the surface following the procedure
on page 63, (Section 8.4.1).
Bonding area too small for
the load on the joint.
Increase bonding area by adding fillets, bonded fasteners or scarf joints. See bonding note, page 65.
Too much clamping pressure squeezed epoxy out
of the joint.
Use just enough clamping pressure to squeeze a
small amount of epoxy from the joint.
Epoxy applied too
1. Use 800 Roller Covers and roll the coating out into
a thinner film. A thin film will flow out much
smoother than a thicker film after it is tipped off with
the foam roller brush.
2. Warm the epoxy to thin it or apply the coating at a
warmer temperature.
Coating curing too slowly.
1. Apply the coating at a warmer temperature.
2. Warm the resin and hardener before mixing to
speed the cure in cool weather.
3. Switch to a faster hardener if possible.
Runs or sags in coating.
Problem solving guide
Moisture from condensation
or very humid conditions
reacts with amines in uncured hardener.
1. Wash and sand cured coating to remove blush.
Cloudiness may appear in the amine blush at the
surface or throughout the coating.
2. Use 207 Hardener for clear coating applications.
3. Use 205 or 206 Hardeners for clear coating only
in dry conditions.
4. Use 207 Hardener for laminating thin veneers that
may allow epoxy to bleed to the surface, especially
when vacuum bagging.
Entrapped air from aggressive roller application.
1. Apply coating at warmer temperature–thinner epoxy.
2. Apply epoxy in thin coats.
Fairing compound (epoxy/407 or 410 mixture)
sags and is difficult to
Fairing material not thick
1. Add more filler to the mixture until it reaches a
“peanut butter” consistency–the more filler added,
the stiffer and easier it will be to sand.
2. Allow the wet-out coat to gel before applying the
fairing material to vertical surfaces.
Waxy film appears on
surface of cured epoxy.
Amine blush forms as part
of the curing process.
Blush formation is typical. Remove with water. See
8.4.1 Special preparation, page 64.
The hardener has turned
red after several years
Moisture in contact with
hardener and metal container.
Red color will not affect epoxy performance.
May not be suitable for clear coating or in exposed
areas where color is not desired.
Epoxy not completely
Allow the final epoxy coat to cure thoroughly. Allow
several days if necessary for slow hardeners at
cooler temperatures. Warm the epoxy, if possible.
Paint incompatible with epoxy.
1. Use a different type of paint. Some single part
polyurethanes are incompatible with the hardener.
If unsure, test for compatibility on a coated piece of
scrap material.
2. Use 207 Hardener.
Epoxy surface not thoroughly prepared.
Remove the amine blush and sand the surface thoroughly before applying paints or varnishes.
See 8.4.1 Special preparation, page 64.
Batch is too large.
1. Mix smaller batches.
2. Transfer the mixture to a container with more
surface area, immediately after mixing.
Temperature too warm for
the hardener.
Use 206 Slow or 209 Tropical hardener in very
warm weather.
Pinholes appear in epoxy coating over
abraded fiberglass or epoxy.
Surface tension causes epoxy film to pull away from
pinhole before it gels.
After applying epoxy with 800 Roller Cover, force
epoxy into pinholes with a stiff plastic or metal
spreader held at a low, nearly flat angle. Recoat and
tip off coating after all pinholes are filled.
Bubbles formed in coating over bare wood or
other porous material.
Air trapped in the wood escapes through coating (outgassing) as the wood's
temperature is rising.
1. Coat the wood as its temperature is dropping– after warming the wood with heaters or during the
later part of the day.
2. Apply a thinner coat, allowing air to escape easier.
3. Tip off the coating with a roller cover brush to
break bubbles.
Clear coating turned
Paint or varnish will not
set up over epoxy.
Epoxy became very hot
and cured too quickly.
Wood data
Wood data
Wood data
Additional reading
Additional reading
Bingham, Bruce. THE SAILOR’S SKETCHBOOK. Camden, ME: Seven Seas, 1983.
BOATS. Camden, ME: International Marine Publishing Co., 1987.
Chapelle, Howard L. BOATBUILDING. New York: W. W. Norton & Co., 1969.
W. W. Norton & Co., 1985.
Editors of WoodenBoat Magazine. WOODEN BOAT: AN APPRECIATION OF THE
CRAFT. Reading, MA: Addison-Wesley Publishing Co., 1982.
Gougeon Brothers, Inc. T H E GO U G E O N B R O T H E R S O N B O A T
CONSTRUCTION. 4th Edition, Bay City, MI: Gougeon Brothers, Inc., 1985.
McIntosh, David C. “Bud”. HOW TO BUILD A WOODEN BOAT. Brooklin, ME:
WoodenBoat Publications, Inc., 1987.
Monk, Edwin. MODERN BOAT BUILDING. New York: Charles Scribner’s Sons,
Skoog, Jim. CRUISING IN COMFORT. Camden, Me: International Marine
Publishing Co., 1986.
Camden, ME: Seven Seas, 1990.
Steward, Robert M. BOATBUILDING MANUAL. Camden, Me: International Marine
Publishing Co., 1980.
RESTORATION HANDBOOK. Blue Ridge Summit, PA: TAB Books Inc., 1981.
Trefethen, Jim. WOODEN BOAT RENOVATION. Camden, Me: International
Marine Publishing Co.
Adhesive fillers, 58
Aluminum, bonding to, 65
Assessing feasability, 2
butt joints in planks, 31
for stiffness, 6
frames, 21
gluing, 65
hardware, 43
joint repair, 22
scarf joints in planks, 30
splines in carvel planking, 29
studs and threaded rods, 46
Butt joints, planks, 31
Carvel planking repair, 27
Cleanup, 56
Clear coating, 51
benefits of, 6
for moisture protection, 50
Commitment, determining, 3
Controlling cure time, 60
Coverage, coating, 72
Cure stages, 59
Damage, inspecting and locating, 11
Dispensing epoxy, 61
Disposal, epoxy, 56
Double planking, repair, 32
Dry rot,
cause, 4
drilling and filling, 15
filling with epoxy, 14
filling with wood, 14
repairing, 13
Epoxy coating, 50
Evaluating damage, 8
Fairing, technique, 68
Fastener bonding, 43
Fillers, description, 57
Fillets, 67
Floors, repair, 23
laminating, 17
replacing, 19
Garboard, repair, 22
Glazing compound, 53
Hardeners, 57
Hardware casting, 45
Hardware, installing, 43
Hazards, 55
Historical value, 3
Inspecting the boat, 8
Joint repair, 22
Joint strength, 65
Keel bolt repair, 25
Keel repair, 25
Laminated skin repair, 37
Laminating, 66
Laminating frames, 17
Lapstrake plank repair, 32
Linear polyurethanes, 52
Manual overview, 2
Mini pumps, using, 61
Open time, 59
Paints, 52
Plastic, bonding to, 65
Plywood skin repair, 33
Pot life, 60
Precautions, health, 55
Preparation for bonding, 63
Primers, 53
Problem solving, 73
Removing epoxy, 63
Repair, definition, 2
Resin, 56
Resin-starved joints, 66
Restoration, definition, 2
Safety, 55
Scarf joint method, 30
Seams, carvel plank, 28
Shelf life,
epoxy, 72
Single-step bonding, 66
Sister frames, installing, 21
Stiffness, loss of, 4
Structural framework, repairing, 17
Structural framework, understanding, 8
Stud bonding, 46
Sunlight, effects of, 48
Surface preparation, 63
Teak veneer deck, installing, 41
Teak, bonding to, 64
Thinning epoxy, 16
Threaded rods, bonding, 46
Two-step bonding, 65, 66
degradation, 48
protection, 50
Using the manual, 2
Vacuum bagging, for laminating, 67
Ventilating for longevity, 7
Ventilation, 54
suitability for repair, 5
Wet-out, 65
Wooden boats,
why they fail, 4
Additional building and repair information available from Gougeon Brothers, Inc.
Publications 002-950 WEST SYSTEM® User Manual & Product Guide
The primary guide to safety, handling and the basic techniques of epoxy use. Includes a complete description of WEST SYSTEM epoxy resin, hardeners, fillers,
additives, reinforcing materials tools, supplies and publications.
002 The Gougeon Brothers on Boat Construction
This book is a must for anyone building a boat or working with wood and WEST
SYSTEM epoxy. Includes extensive chapters on composite construction techniques, materials, lofting, safety and tools, with many illustrations, diagrams and
002-550 Fiberglass Boat Repair & Maintenance
A complete guide to repair fiberglass boats with WEST SYSTEM Epoxy. Includes
illustrated procedures for structural reinforcement, deck and hull repair, hardware installation, keel repair and teak deck installation.
002-650 Gelcoat Blisters-Diagnosis, Repair & Prevention
A guide for repairing and preventing gelcoat blisters in fiberglass boats with
WEST SYSTEM Epoxy. Includes an analysis of the factors that contribute to blister formation and illustrated steps for preparation, drying, repairing and coating
for moisture protection.
002-150 Vacuum Bagging Techniques
A step-by-step guide to vacuum bag laminating techniques for bonding wood,
core materials and fabrics with WEST SYSTEM Epoxy. Discusses theory, molds,
equipment and techniques used to build composite structures.
002-740 Final Fairing & Finishing
Techniques for fairing wood, fiberglass, and metal surfaces. Includes fairing
tools, materials and a general guide to finish coatings.
Video 002-892 Basic Application Techniques
A video primer on WEST SYSTEM Epoxy Products and their use. Includes safety
procedures and application tips for coating, bonding and fairing. VHS–20 min.
002-894 Fiberglass Repair with WEST SYSTEM Brand Epoxy
A guide to structural repair on fiberglass boats. Covers repairs to cored and
non-cored panels and how to apply gelcoat over epoxy repairs. VHS–20 min.
002-896 Gelcoat Blister Repair with WEST SYSTEM Brand Epoxy
A guide for repairing and preventing gelcoat blisters on fiberglass boats. Includes an analysis of the factors contributing to blister formation and steps for
preparation, drying, repairing and coating for moisture protection. VHS–16 min.
002-970 Wooden Boat Restoration & Repair
Published by
Gougeon Brothers, Inc.
PO Box 908
Bay City, MI 48707
(989) 684-7286
Fax (989) 684-1374
6th Edition · Printed 04/03
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