water-based finishes andhvlp sprayers make it

WATER-BASED FINISHES AND
HVLP SPRAYERS MAKE IT EASY
Picture this if you will. You just completed a project that required hundreds of
dollars worth of wood, using thousands of dollars of woodworking machinery.
Now, are you going to apply the finish with a $5 brush? We hope not. If you’ve
always admired the smooth, rich looks that come with a spray finish, but avoided
the process because of all the complications, take heart. Help has arrived.
You can achieve professional results in
a home shop
Woodworking pros know the value of a
sprayed-on finish. But conventional
spray guns and solvent-based finishes
demand expensive equipment and shop
setups that most of us home
woodworkers cannot afford. Now there’s
a better, safer way--combining HVLP
spray equipment with water-based
finishes.
HVLP stands for high-volume, lowpressure. In contrast to conventional
spray guns, which blast out air at up to
40 pounds per square inch, HVLP units
need only 4 to 10 psi to get the job done.
The result: Up to 85 percent of the finish
lands on the workpiece compared with
35 percent for conventional sprayers.
You waste less finish, and you don’t coat
everything in your shop with overspray.
The second ingredient to this winning recipe is a water-based finish. Unlike oil-based
finishes, water-based finishes don’t give off toxic, flammable fumes. With them, you
don’t need an explosion-proof ventilation system, and you can safely spray waterbased finishes in the basement or a shop attached to your house.
Taking advantage of the opportunities offered by HVLP systems and water-based
finishes does require some education, though. So here’s our five-step program to get
you started on the kind of woodworking finish you’ve always wanted.
Choose your equipment wisely
Here are samples of three different types of
HVLP sprayers. The three-stage turbine-based
Accuspray 23i, left, the Binks Mach I CAS gun in
the middle, and the single-stage Wagner
Professional FineCoat.
Manufacturers offer two different types of HVLP setups: turbine-based machines that
pump their own air and conversion-air systems (CAS) that hook up to an air
compressor. Below, we compare the two systems, but for the techniques in this
seminar, we’ll concentrate on the turbine-based systems because they usually are
better suited to the home woodworker.
Turbine-based systems. The beauty of turbine-based systems is that they send out a
warm stream of air and finish. This helps water-based finishes dry faster and flow out
smoother, particularly during periods of high humidity. Portability also ranks high on
the list of advantages. You can carry these compact units by hand or roll them around
in the shop.
Turbine-based spray systems have one or more blowers that force air through a 1"diameter hose and into a spray gun. They are rated as one, two, or three stage,
corresponding to the number of blowers. Extra blowers increase the pressure of the air
coming out the gun, which helps spray thick-bodied finishes and speeds up work on
larger projects. The one-stage machines do a fine job of spraying water-based
polyurethanes, as well as paints and oil-based products that are thinned according to
manufacturers instructions. A two-stage machine will handle unthinned finishes and
larger projects better, and three-stage machines are used primarily by production
shops. Prices for one-stage systems range from $180 to $350, two-stage turbines sell
for about $300 to $800, and three-stage units cost around $900 to $1,200.
Conversion-air systems (CAS). CAS sprayers rely on air coming from an air
compressor. Changing this high-pressure air to low-pressure, high-volume air requires
a specialized CAS spray gun, or a pressure-conversion regulator that attaches to the
air inlet port on an HVLP gun.
This might seem like a way to get into the HVLP game without spending a lot of
money because all you buy is the gun. But CAS guns generally cost $250 to $350.
They also require a compressor with a minimum of 3 to 5 hp and an air-delivery rate
of at least 10-20 cfm at 60-80 psi. With a large compressor, however, CAS systems do
a nice job of atomizing thick finishes.
A potential source of problems with CAS sprayers is the oil or water that occasionally
gets into the hose of an air compressor. To eliminate these contaminants, you must
attach a filter to the air outlet on the compressor.
Get to know water-based finishes
The techniques you may have used in applying oil-based finishes won’t always work
with water-based products. Knowing the do and don’ts of water-based finishes will
prevent problems and improve your results.
How to control grain raising.
All water-based finishes, sprayed or not, will raise the grain of your wood. The
solution? Put on a light first coat, and let it dry. Then, lightly sand the surface with
220-grit sandpaper. Be careful not to sand through the finish and into the bare wood.
Subsequent coats will not raise the grain.
Whatever you do, never smooth a water-based finish with steel wool. Small fragments
of steel will become embedded in the finish and create rust stains.
The importance of gun cleanup.
When spraying water-based finishes with an HVLP system, the finish can dry out
inside the nozzle of the gun within minutes after you stop spraying. Once these
finishes dry, no solvent will remove them. You’ll have to scrape them out, and this
can take hours. To prevent this problem, be sure to clean your gun and its parts
immediately after you finish spraying.
Set up your shop for spraying
Finishing wood is 90 percent preparation and 10 percent application, and that holds
true with HVLP systems and water-based finishes. Here are the things you need to do
to your shop before turning on the spray gun.
Light to see the work.
With your work light in the correct position, you’ll be able to see the thickness of the
finish you’re applying and any flaws, such as sags or runs. The secret lies in
positioning yourself and your light so that you can see the light's reflection in the
finish on the workpiece. Set up your light as shown in the photo below, and spray a
few test pieces to make sure you can see the results clearly.
Guard against overspray.
Even though HVLP systems greatly reduce overspray, you should still plan to control
it. Cover your tools and workbenches with drop cloths, or hang an old shower curtain
or other barrier around your work to avoid spraying the walls.
Position yourself and the work light so you
can see the reflection of the light in the
sprayed surface.
Nix the dust for top results.
Fast-drying sprayed finishes don’t collect dust like brushed-on finishes, but you
should minimize airborne dust anyway. Clean and vacuum the area thoroughly. Turn
off all fans, including the heating or air conditioning. You also may want to mop the
floor with water to keep down static electricity, which attracts dust. Turbine-based
HVLP units draw in a lot of air, and this may stir up dust.
Wear a respirator and goggles.
Water-based finishes impart very little odor, but avoid inhaling the mist from the
spray gun. When spraying, wear a snug-fitting respirator with a replaceable organicvapor cartridge. Replace the filter when you can smell odors through the respirator.
Cotton dust masks won’t suffice because they don’t neutralize organic vapors.
Prepare the gun and finish
Successful spray-finishing requires a lot of small, but simple adjustments at this step.
You may need to thin the finish and tweak the settings on the gun until you get a
perfectly even flow.
Thin and strain the finish.
Although most manufacturers of water-based finishes don’t recommend thinning
products more than 5 percent, you may want to thin other finishes, such as
polyurethanes or paints. You’ll find directions for thinning on the labels of most
finishes.
You must, however, strain any finish you spray to get rid of lumps or contaminants, as
shown below. Most hardware stores sell disposable paper strainers you can use for
this purpose.
Select a pattern. The air horns on the front nozzle of a spray gun enable you to adjust
the shape of your spray pattern. Turn the horns horizontal for a vertical pattern, or
vertical for a horizontal pattern. Set the horns at 45 degrees for a circular pattern. Test
your spray pattern on a piece of scrapwood until you get the desired shape. Use a
vertical pattern for spraying panels, a horizontal pattern for narrow vertical
workpieces, and a round pattern for round or circular objects. For most HVLP spray
guns, keep the nozzle about 6-10" from the workpiece to obtain the best results.
Strain the finish through a disposable filter
available at hardware stores.
Adjust the fluid-to-air ratio.
The next step is to adjust your finish flow to get the proper amount of finish on the
work surface. You increase or decrease the amount of finish by turning a knurled
knob located at the rear of the gun just above the handle.
Start with the fluid control set at the minimum and increase the amount of fluid until
the finish on your test piece starts to run or sag. Then, reduce the amount of fluid until
the runs stop. If you get a surface that has a texture similar to that of an orange-peel,
you need more finish.
Turning the air horns on the front of the
spray gun enables you to change the shape of
your spray pattern.
Adjust the fluid control knob at the rear of the
gun until you get the proper amount of finish
on a test panel.
Start your spray guns
Having tuned up the equipment and prepared the finish, all you have to do now is
spray the parts of a project in the correct order and maneuver the gun properly. Start
spraying on the edges and corners, saving the large areas and panels for last. On
enclosed structures, such as boxes and drawers, spray the inside first.
To avoid the natural tendency to pivot the gun from the wrist or elbow, move your
arm from the shoulder. And be sure to maintain a constant speed with the gun.
OUTSIDE CORNERS. Aim the spray gun so the
corner splits the spray pattern down the middle.
INSIDE CORNERS. Spray down each side with a small overlap in the corner.
EDGES. Aim so the center of the spray pattern hits the center of the edge.
PANELS. Start by triggering the gun before the spray pattern hits the workpiece. Do
not let go of the trigger until the spray pattern has completely left the workpiece.
Overlap each spray pattern 50 percent, and work in a back-and-forth motion.
GUN TRAVEL, ROUND OBJECTS. Keep the gun equidistant from the project
during the entire spraying motion. If you cannot maneuver around your project easily,
mount it on a lazy Susan. That way, you can rotate the project 360 degrees.
GUN TRAVEL, FLAT OBJECTS. The nozzle of the spray gun should travel along
a straight path that’s parallel to the object being sprayed. If you spray in an arc, you’ll
apply too little of the finish on the ends, which causes orange peel. Too much in the
middle causes runs or sags).
Tips on spraying other
products with HVLP
HVLP systems work for more than just water-based finishes. Here are the other
options available.
Paint.
You can spray oil- or latex-based paint with most HVLP systems, but you may have
to thin the paint anywhere from 10 to 30 percent to achieve smooth results. Follow
manufacturers recommendations on thinning, and spray a few test panels before
applying paint to a project. If thinning doesn’t work, you can buy accessory air
nozzles for spraying thick finishes.
Oil-based polyurethanes.
Oil-based polyurethanes usually require thinning. But unless you have an extensive
ventilation system with an explosion-proof fan, you must spray these oil- or solventbased products outside in a spark-free environment.
Lacquer.
Because of its quick-drying nature, lacquer usually does poorly in an HVLP spray
system. The warm, turbine-driven air causes the lacquer to dry prematurely, leading to
an orange-peel texture. With their cooler air delivery, however, CAS systems do a
good job with lacquers. Like oil-based products, lacquer requires extensive ventilation
precautions due to its toxic and flammable fumes.
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