Green Brick Making Manual.indd - Knowledge Partnership Programme

Green Brick Making Manual.indd - Knowledge Partnership Programme
Green Brick Making Manual
A Practical Guide on How to Make Green Bricks
Contact Details:
Technology and Action for Rural Advancement
B-32, TARA Crescent,
Qutub Institutional Area,
New Delhi-110016
Phone Number: 011-26544100
Email: [email protected], [email protected]
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©Technology and Action for Rural Advancement 2014
Preface
This manual has been developed in response to the interest in
Malawi to understand the process of production of green bricks.
It aims to describe the different methods of production of green
bricks. The manual also explains in detail the methods of testing
of soil for determining its suitability in brick making and the drying,
stacking and storage of green bricks.
This user manual is expected to serve as a basic tool for the workers
and supervisors in a kiln to delineate the essential parameters of
producing green bricks.
This manual doesn’t claim to be complete or perfect. It is in the
hands of users to utilise it fully by using it as a reference guide
for further improvement. The authors would appreciate if you
could share your ideas and work experiences to further improve
this manual.
Society for Technology and Action for Rural Advancement, India.
Acknowledgments
During the course of developing this manual, every effort was made
to include the existing knowledge base, along with interactions
between personnel associated with the technology.
We would like to acknowledge the support of various organizations,
TARA Machines and Tech. Services Pvt. Ltd., India; Centre for
Community Organization and Development (CCODE), Lilongwe,
Malawi; Eco bricks Limited, Lilongwe, Malawi and IPE Global, New
Delhi; who have whole heartedly contributed towards developing
the same. Our sincere thanks to various individuals, whose views
have been accessed personally, through one-to-one interactions, the internet and printed documents.
The research efforts captured in this manual would not have been possible without the institutional support
given to the project organisations by Deutsche Gesellschalt fur Internationale Zusammenarbeit (GIZ)
GmbH and the Knowledge Partnership Programme (KPP) of the Department of International Development
(DFID), India. Managed and supported by IPE Global, the KPP aims to step up collaboration around ideas,
knowledge, evidence, accountability, technology and innovation, impacting the delivery of global public
goods and services and leverage Indian experiences to reduce poverty in LDCs.
Society for Technology & Action for Rural Advancement, India
Contents
Chapter 1: Appropriate Soils for Brick Making........................................................8
1.1 Introduction ................................................................................................................ 8
1.2 Origin and Formation of Soil ..................................................................................... 8
1.3 Formation of Soil ........................................................................................................ 9
1.4 Types of Soils in Malawi ............................................................................................. 9
Chapter 2: Soil Suitability in Brick Making ............................................................11
2.1 Additives .................................................................................................................... 11
Chapter 3: Preparatory Work before Construction ..............................................13
3.1 Introduction .............................................................................................................. 13
3.2 Visual Test ................................................................................................................. 13
3.3 Field Test ................................................................................................................... 14
3.4 Laboratory Tests ....................................................................................................... 17
Chapter 4: Choice of Brick and Production Options .............................................19
4.1 Introduction .............................................................................................................. 19
4.2 Brick Types and Choice ............................................................................................ 19
4.3 Use of Internal Fuel in Making of Green Bricks ..................................................... 20
Chapter 5: Green Brick Production Process ..........................................................22
5.1 Introduction .............................................................................................................. 22
5.2 Necessary Conditions for Green Brick Making ...................................................... 22
5.3 Standarisation of Green Bricks ............................................................................... 25
5.4 Stages of Green Brick Making ................................................................................. 27
5.5. The Moulding Process.............................................................................................. 38
Chapter 6: Drying, Stacking and Storage Process .................................................41
6.1 Introduction ...............................................................................................................41
6.2 Drying Principles .......................................................................................................41
6.3 Factors Affecting Brick Drying .................................................................................42
6.4 Behaviour of a Brick during Drying................................. ....................................... 42
GREEN BRICK MAKING MANUAL
5
VERTICAL SHAFT BRICK KILN
6.5 Determination of Drying ....................................................................................... ........ ............. 43
6.6 Stacking Patterns and Its Effect on Drying ................................................................. . ............. 43
6.7 Process of Natural Brick Drying ........................................................................ ............ ............. 44
6.8 Various Stacking Patterns and Storage of Green Bricks .......................................... .. ............. 44
Figures
Figure 1 Red Soil .................................................................................................................... ............. 9
Figure 2 Black Soil ................................................................................................................. ............. 10
Figure 3 Alluvial Soil ......................................................................................................... ..... ............. 10
Figure 4 Boiler Ash as Internal Fuel ..................................................................................... ............. 12
Figure 5 Fly Ash as an Anti-Shrinkage Material ........................................................... ....... ............. 12
Figure 6 Ball Test for Determining Suitability of Soil for Use in Brick Making ................ ............. 14
Figure 7 Sedimentation Test for Determining Suitability of Soil for Use in Brick Making............ 14
Figure 8 SmearingTest for Determining Suitability of Soil for Use in Brick Making ....... ............. 15
Figure 9 Crumbling Test for Determining Suitability of Soil for Use in Brick Making ..... ............. 15
Figure 10 Pencil Test for Determining Suitability of Soil for Use in Brick Making .......... ............. 16
Figure 11 Ball Shape Test for Determining Suitability of Soil for Use in Brick Making... ............. 16
Figure 12 Lemon Test for Determining Suitability of Soil for Use in Brick Making ..................... 16
Figure 13 Burnt Clay Bricks .......................................................................... ..................... .. ............. 19
Figure 14 Sand Lime Bricks .................................................................................................. ............. 20
Figure 15 Tobacco Dust as Internal Fuel ............................................................................. ............. 20
Figure 16 Black Core in Fired Bricks .................................................................................... ............. 21
Figure 17 Reduction Spots in Fired Red Bricks ................................................................... ............. 21
Figure 18 Manual Mixing Process ........................................................................................ ............. 29
Figure 19 Rotovator ................................................................................................. ............. ............. 32
Figure 20 Wet Mixing ............................................................................................................ ............. 33
Figure 21 Slop Moulding ....................................................................................................... ............. 33
Figure 22 Soft Mud Moulding Machine ............................................................................... ............. 38
Figure 23 Different Patterns of Stacking ............................................................................. ............. 43
Figure 24 Storage of Green Bricks ....................................................................................... ............. 44
6
GREEN BRICK MAKING MANUAL
Tables
Table 1 Comparison of Chemical Analysis of Good and Ordinary Soil Sample for VSBK Firing 17
Table 2 Properties of Good Brick Making Soil .................................................................... ............. 18
Table 3 Shrinkage Rates and Mould Sizes .......................................................................... ............. 27
Table 4 Interior Mould Sizes................................................................................................. ............. 36
GREEN BRICK MAKING MANUAL
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VERTICAL SHAFT BRICK KILN
Chapter 1
Appropriate Soils
for Brick Making
1.1 Introduction
The history of brick making goes back to the
earliest days of civilization. It is averred that
bricks were made more than 10,000 years ago.
Although such great antiquity cannot yet be proved,
archaeologists working at various sites have more
or less accurately determined that the burned and
the unburned bricks in the lower levels of the great
temple were made more than 5,000 years old.
Successive civilizations in the Euphrates – Tigris
delta used clay bricks for building their houses,
palaces and temples; many of the original bricks,
such as those used in the 6th century BC to build
Babylon, were taken from the ruins to build the
towns of Ctesiphon and Baghdad. Out of Western
Asia the art of brick making appears to have spread
westward towards Egypt and the Mediterranean
and eastward to China and India.
Soil is formed by weathering of rocks. It is a
lengthy process and takes millions of years for its
formation. Thus it is an extremely valuable resource
and should be used judiciously for making bricks.
It is essential to be aware of the properties of
soil before use in brick making. These are usually
referred to as plasticity, grain size, organic content,
colour and other chemical properties. All these
properties need to be judiciously studied before
determining the suitability in making bricks.
1.2 Origin and Formation of Soil
8
chemical compounds known as minerals. Many of
these minerals in turn combine together to form
aggregates which is known as rocks.
Rocks are divided into three main groups according
to their origin and structure.
Igneous Rocks
Igneous rocks are those that have been formed
by the action of heat. These rocks were the first
to be formed when the molten mass cooled and
consolidated into solid rock. The igneous rocks
constitute nearly 25% of the earth’s crust and
are sometimes even 15 km thick. These rocks are
mostly crystalline in nature and occur in big masses.
Sedimentary Rocks
These rocks have formed through the action of
water. They form from sediments brought by
water. Hence they are called sedimentary rocks.
The sediment may consist of various types of
substances and of various sizes of particles. These
particles are cemented together by substances
like silica, iron oxide or lime to give a solid form.
Most of these rocks are deposited in layers or
strata. All sedimentary rocks are of secondary or
derivative origin, as they consist of materials that
have previously existed on or beneath the surface
of the earth. The transportation, accumulation
and consolidation of these materials give rise to
new rocks.
Soil Forming Rocks
Metamorphic Rocks
The earth’s crust (outer solid later) is principally
composed of mineral matter. The mineral matter
is made up of various elements combined together
to form compounds. Almost all the elements are
present in the earth’s crust (e.g. oxygen, silicon,
iron, calcium etc.). Each element is in combination
with one or more elements to form definite
Metamorphic rocks have resulted from the
subsequent transformation of igneous and
sedimentary rocks under the influence of heat,
pressure and chemically active liquids and gases.
When the change is considerable, the rocks are said
to have undergone metamorphosis and the new
rock is known as a metamorphic rock.
GREEN BRICK MAKING MANUAL
1.3 Formation of Soil
1.4 Types of Soils in Malawi
The transformation of rocks into soil is termed as
soil formation or soil development. Soil formation
starts primarily with the weathering of rocks. The
weathering processes are primarily destructive in
nature and help to change the consolidated rocks
into unconsolidated soil.
Soils relevant to brick making in Malawi can be
divided broadly into following major groups.
Weathering processes are of two types:
Physical Weathering
It is a mechanical process, causing disintegration
of massive rocks into smaller particles without any
chemical change or formation of newer products.
Physical weathering is caused by the following
factors.
Temperature
The alternate expansion and contraction of rocks
due to variation in temperature produce cracks.
The number of cracks slowly increases and the rock
gets broken into pieces.
Water
Red Soil
Red colour in red soils is due to the presence of
various oxides of iron. They are either formed in-situ
or from products of decomposition of rocks washed
to a lower level. They generally include soils locally
known as red sandy soils and red alluvium. They
are mostly formed under sub-humid climate from
an assorted rock formation. Their main features
are light texture, porous structure, absence of lime
and organic matter. In the upper part of a typical
stratum, silty red soils are found. With depth the
clayey fraction increases with the presence of
granular particles of morrum or stones.
These types of soil are suitable for brick making with
a deep cherry red fired colour. However, due to its
high presence of silt and sand particles appropriate
strength is not developed. Caution should be
exercised in selecting these kinds of soils since at
depths they might contain coarser particles. (Refer
Figure 1)
In cold regions, water freezes in rock joints and
expands in volume. Due to this tremendous
pressure the rock splits into loose mass of stones.
Rain water falling on the rocks also causes some
abrasion. Moving water due to rains in rivers and
flood plains has tremendous transport capacity and
by its rolling actions further grinds the stones into
smaller pieces. Water through its erosion forces
removes the weathered parts and deposits as fine
sand, silt or clay.
Wind
Wind carrying particles in suspension, like sand
from rock fragments, when blowing constantly
over a rock at great speed exerts a grinding action
whereby the rock gets disintegrated.
Chemical Weathering
Chemical weathering takes place mainly at the
surface of rocks with the dissolution of soluble
minerals and formation of secondary products.
This is called chemical transformation. No chemical
weathering is possible without the presence of
water. The rate of chemical reactions increases
with dissolved carbon dioxide and other solvents in
water. Higher temperatures and humid climates also
greatly aid in chemical weathering. This is the reason
of finding high amount of soil in tropical climates.
Figure 1: Red Soil
Lateritic Soil
They are found mostly in areas of high rainfall. They
are light in texture and have an open free draining
structure. They are deficient in lime and thus highly
suitable for brick making. Laterite soils formed at
high levels have a pale red colour and are highly
gravelly in composition. Those formed at lower
levels have a darker colour due to accumulation of
humus and a slightly finer texture.
These types of soils are also suitable for brick
making. However due to sandy nature they must be
GREEN BRICK MAKING MANUAL
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VERTICAL SHAFT BRICK KILN
well compacted by mechanical means (pugmilling)
to avoid breakage and attain the desired strength.
Black Soil
Black soils are developed from Basaltic rocks
under semi-arid conditions. The soils are typically
black or dark brown in colour with high content
of lime nodules. They are locally known as regur,
or black cotton soil, deep and medium black soils.
Their texture ranges from sandy clay to heavy clay.
Some black soils are porous. However majority of
them are highly compact and impervious. One of
Figure 3: Alluvial Soil
varies from sandy clay to silty clay and even clayey
in case of river delta areas. The structure is also
variable, loose and free draining in case of sandy
soils and compact and impervious in case of clayey
soils. Due to its medium plasticity and high silt
content, they are most suitable for brick making.
(Refer Figure 3)
Desert Soils
Figure 2: Black Soil
the characteristics of black soil is that it swells on
wetting and shrinks and cracks when dry. These
types of soils are highly unsuitable for brick making
as a whole. (Refer Figure 2)
Alluvial Soil
Alluvial soils are the best available soil for both
agriculture and brick making. These types of soils
are characterised by extreme depth and yellowish
to grey or grayish brown in colour. The texture
10
GREEN BRICK MAKING MANUAL
They have been developed in arid regions mostly
under the influence of physical weathering. They
are mainly sandy and contain varying proportions
of lime. These types of soils are unsuitable for
brick making.
Saline and Alkaline Soils
These soils are developed in arid and semi arid
regions. Poor drainage is also responsible for their
development. Due to high salt content, these types
of soils are unsuitable for brick making. Although
in some parts of coastal India evidences of brick
making are found, the fired brick quality are poor
and are characterized by salt petering.
Chapter 2
Soil Suitability in
Brick Making
A brick production unit needs to have a good quality
soil to produce a high strength green brick. The
better the green brick, better the fired properties.
Certain types of clay are not good for brick making.
For example, soils with high sand content have
no plasticity and are difficult for forming. After
moulding these types of bricks will deform on its
own dead weight and are liable to crack during
handling. Similarly the soil used for making pottery
is not good for making bricks because it has a high
shrinkage rate which causes the brick to crack
during drying.
To select the proper soil for brick making, generally
select an area which has a tradition of brick making.
For non brick making areas the soil from varying
areas and depths should be tested for suitability
in brick making.
The most important criteria for a go or no go are
the following:

Soil should not contain any lime

Soil should be free of stone particles

Soil should be plastic i.e. it should retain its
formability
For simple field tests to check the quality of clay
refer to Chapter 3. However, these processes
are indicative only and will only give you an idea
of the soil. For confirmative tests it is always
recommended to get your soil tested from an
accredited laboratory.
Based on field trials it is generally assumed that
from a 135 ft x 135 ft land, dug upto 2 ft depth,
approximately 6 lakhs of green bricks can be
produced. Thus for a 2 shaft VSBK producing
around 25 lakh bricks per season, one would
require approximately 540 ft x 540 ft of land.
However the requirement of land will decrease if
the soil depth is more that 2 ft.
2.1 Additives
In green brick making additives are of the following
types:

Internal fuel

Anti shrinkage material

Structure opening material
Internal Fuel
For firing of green bricks in VSBK in an energy
efficient manner, addition of internal fuel is an
absolute necessity. Without internal fuel content,
firing of green bricks in a VSBK is not recommended.
Internal fuel not only reduces the external fuel
consumption but also saves on the emission
thereby reducing pollution.
Internal fuel is a waste materials produced by
process industries. They include

Tobacco industry waste

Boiler ash

Textile industry sludge

Coal dust of inferior quality

Distillery industry waste

Agro industry waste

Bottom ash from sugar manufacturing industries
These are dumped by the industries and are mostly
available free of cost. It is mixed with the soil
during its dry mixing process. Quantity of addition
depends on the quality of the soil and the internal
fuel. (Refer Figure 4)
GREEN BRICK MAKING MANUAL
11
VERTICAL SHAFT BRICK KILN

Stone dust

Sandy soil
Before addition refer to an expert for determining
the quantity to be added. Too much addition might
affect the fired brick property. (Refer Figure 5)
Structure Opening Material
Figure 4: Boiler Ash as Internal Fuel
Anti Shrinkage Material
To make highly plastic soils suitable for brick
making anti shrinkage materials are added. This is
to avoid high shrinkage and resultant cracks during
drying in the open atmosphere. Depending upon
the availability the following types of anti shrinkage
materials can be added

Fly ash

Fine sand

Medium sand (< 2 mm grain size)
In areas of very low humidity and high temperature,
a structure opening material is used in green brick
making. This is sometimes in addition to the anti
shrinkage material also. The materials generally
used are

Rice husk

Wheat straw

Saw dust
These types of materials are used only during the
summer months. They are used within the green
brick to delay the shrinkage rate of green bricks
during drying. These types of materials are added
to a maximum of 2% only depending upon the
plasticity of the soil. Too much addition reduces
the property of the fired brick.
Figure 5: Fly Ash as an Anti-Shrinkage Material
12
GREEN BRICK MAKING MANUAL
Chapter 3
Preparatory
Work before
Construction
3.1 Introduction
The quality of fired bricks depends largely upon the
soil properties, skill of the moulders and firemen,
no matter which technology is used for firing
the bricks.
The basic constituents of soil are the clay and silica
minerals which contain minerals like alumina,
potassium, iron, calcium, sodium etc. These mineral
constituents have various characteristics on brick
forming, drying and firing. Good brick quality cannot
be achieved from all types of soil. The only way to
determine the fired brick quality from a particular
soil is to make the desired product on a trial basis
and analyse the results. Confirmatory tests of soil
are also performed to explain and understand the
product quality.

Site should not be nearby the river areas,

Site must be free from tree plantation, (because
of probability of high organic content within the
soil e.g. roots, leaves etc. Further tree plantations
will provide a shadow on the green bricks thus
taking more time to dry.)

Site should not be near forest area to prevent
damage to forest trees by the emissions from
the firing process.
VSBK Soil Selection

Soil should not contain any limestone (because
presence of limestone particles greater than 1
mm gives lime bursting in a fired brick)

Soil should be free of stone particles (because
presence of stone particles damages the brick
during the firing process due to unequal thermal
expansion).

Soil should be plastic i.e. it should retain its
formability for forming a strong green brick.
Soil Suitable for Brick Business
The very first step to determine the first feasibility
of soil for a brick production site is to check its
quality and availability. For economic viability, it has
been calculated that a VSBK business requires the
local available soil for a period of atleast 3-5 years.
Therefore soil suitability is connected with VSBK site
selection criteria. This is done by visual inspection
of site and performing primary soil tests at site and
soil reserve calculation.
3.2 Visual Test
The visual test gives a quick go or no go decision
for selecting the brick production soil for further
testing. The following rough criteria should be
considered:
VSBK Site Selection

Enough soil at site to last for a period of 3–5
years keeping the economics of brick business
point of view.
Soil Reserve Calculation
The soil reserve calculation is needed for mainly
two reasons:

To ensure that the raw material last for a
period that guarantee that the initial business
investment can be recovered and profit can
be achieved.

To ensure that the same raw material quality
is available for producing consistent quality of
fired product.
GREEN BRICK MAKING MANUAL
13
VERTICAL SHAFT BRICK KILN
3.3 Field Test
There are a few basic field tests that an experienced
brick maker or VSBK technology expert must
master. Although indicative, a good professional
will always derive the correct conclusion out of the
field based tests.
Ball Test
Ball test is mainly for determining sand and clay
proportion in the soil. This test is very essential for
soil having high plasticity and low silica content,
because quantity of sand and water to be added
for the proper plasticity can be found out. (Refer
Figure 6)
Take a handful of soil and put some water in it.
Water should not be too high to make slurry out of
the mixture. It should be enough to make the soil
moist and make dough by hand.
With the hand and fingers mix the soil and water
thoroughly. After uniform mixing try to make a ball
out of the soil. This activity might take some time
depending on the amount of water added. If the
water content is more then add more dry soil.
After the ball is reasonably well formed, drop the
ball from a height of atleast 1 m. Alternatively, the
ball can be dropped from shoulder height with
hands straight. Take care that the surface on which
the ball is dropped is levelled and clean – preferably
a concrete surface or a hard surface. Never do the
test in a wet or a loose surface.
Observe the ball on the floor. If the ball retains
its shape with little amount of deformation at the
bottom only, then the soil is plastic clayey in nature.
However if the ball flattens out upon hitting the
floor, then the soil is sandy in nature.
Take another ball and dry it under atmosphere or
under a small open fire. Cool the ball and repeat
the test. If the ball cracks into many pieces after
contact with the floor then the soil is sandy in
nature. However, if the ball breaks into two to three
pieces then the soil is clayey and plastic in nature.
Sedimentation Test
Observe the smoothness of the surface of the
ball. For plastic soils the surface will be shiny and
uniform. However, for sandy soils it will be difficult
to make a round shaped ball.
Figure 7: Sedimentation Test for Determining
Suitability of Soil for Use in Brick Making
This process is also known as “Bottle Test” for
determining the proportion of clay and sand
particles in the soil. It also gives the idea of
percentage mixture of sand and clay in the soil.
(Refer Figure 7)
Fill one-fourth quantity of the glass beaker with
the required soil. Add half teaspoonful of salt
into the soil. Add water to about 50% above the
soil level. Wait for a few minutes till the water
percolates to the bottom (there will be a distinct
colour difference). Stir the soil and water mixture
vigorously with a spoon for at least 2-5 minutes. The
colour of the stirred material should be uniform.
Figure 6: Ball Test for Determining Suitability of Soil
for Use in Brick Making
14
GREEN BRICK MAKING MANUAL
Pour the stirred slurry into the measuring cylinder.
Add some more water in the beaker and drain off
the entire soil into the measuring cylinder. Take
care that no soil is attached to the sides of the
measuring cylinder.
Place the measuring cylinder on a level platform
and allow it to stand for atleast 12 hours or until
the water becomes clear at the top.
When the water is clear, measure the height of the
sand (h1), silt (h2) and clay (h3) layers.
The respective sand, silt and clay content are
calculated in percentage by dividing the respective
heights with the total height (h1+h2+h3) and
multiplying by 100.
Let the thumb dry out. After drying if the soil layer
falls off easily or can be removed then the soil
is sandy or silty in nature without any plasticity.
However if the soil stick to the thumb and index
finger after drying the it is plastic in nature.
Observe for coarser particles in the soil smear. It
gives a measure of the coarse sand in the soil.
Finger Crumbling Test
Smearing Test
In the field after digging
the land upto the
required depth take
out a small quantity of
the required soil. (Refer
Figure 9)
After the required
depth of soil is reached
take some loose soil
(found near the dug
out area) and put a
little bit of water into it.
Alternatively a soil lump
may also be taken.
Take care not to put
too much of water and
make a watery paste.
(Refer Figure 8)
After the soil is
saturated with water,
mix the soil and water
on the left hand. With
the soil a ball should
be tried to make. Roll
the moist ball in hand
enough so that the
ball is dried out to a
little bit.
Figure 8: Smearing
Test for Determining
Suitability of Soil for
Use in Brick Making
Pinch out a little bit
of the soil with the
thumb and the index
finger and smear on
the thumb by the
index finger at one go.
The smearing should
be done as fine as
possible.
During this process observe for any coarse particles.
It will be felt by the fingers. After the smearing, the
soil does not form a smooth and thin layer, then
the soil is sandy.
To know the plasticity
of the layers of soil, this
test can be performed
whenever intended
to, since it is not an
expensive one and
takes a few seconds to
perform.
Figure 9: Crumbling
Test for Determining
Suitability of Soil for
Use in Brick Making
Take two button sized
(preferably smooth
surface) soil lumps.
The soil lumps should
be sized so that it can
be held between two
fingers e.g. thumb and
index finger.
Press lightly the two fingers on the soil lumps.
Increase the pressure as and when required.
If with low to medium pressure the two soil lumps
gets pressed against each other and cracks, falling
apart into a several pieces then the soil is likely to
be silty or sandy with no plasticity.
If with the maximum pressure, the soil buttons
does not disintegrate or gets broken into two
to three pieces only, the soil is a semi plastic to
plastic soil.
Take care to perform this test repeatedly for three
to four times to get the approximate idea. Before
doing the test, take care that both the soil being
tested are of the same quality.
If the thin soil layer is shiny and evenly spread out
over the thumb then the soil is plastic in nature.
GREEN BRICK MAKING MANUAL
15
VERTICAL SHAFT BRICK KILN
Pencil Test
Take a handful of soil
and put sufficient
water in it to enable to
roll out a pencil out of
the soil. Take care to
mix the soil in hand for
some time. This is to
allow some plasticity
being developed within
the clayey particles of
the soil. Water should
not be too high to
make slurry out of the
mixture. It should be
enough to make the
soil moist and make
dough by hand. (Refer
Figure 10)
Figure 10: Pencil
Test for Determining
Suitability of Soil for
Use in Brick Making
With the hand and
fingers mix the soil
and water thoroughly.
After uniform mixing,
place the moist soil on
the two palms and try
to roll out a fine pencil
out of the soil.
The diameter of the rolled soil should be enough
as per a pencil; not too thick or too thin.
If the soil forms a pencil long enough without
breaking or disintegrating, then it is indicative of
a plastic soil. However if the soil length breaks out
then the soil is non plastic sandy in nature.
Ball Shape Test
and uniform ball. If after
repeated attempts the
soil daub does not form
into a round ball, then
the soil is sandy. During
this process, if water is
released out of the ball
then the soil is silty /
sandy. However if after
a few attempts, a good,
smooth and round ball
is formed, then the soil
is semi plastic to plastic
in nature.
Wash hands with water.
If washing is easy then
the soil is silty / sandy
with low clay content.
However even after
repeated washing, soil
is sticking into the palms
then the soil is clayey in
nature.
Figure 11: Ball Shape
Test for Determining
Suitability of Soil for
Use in Brick Making
After washing if soil sticks to the corners of the
finger nails then the soil has high clay content.
Lemon Test
Take a lump of soil from the required area or depth.
Try to avoid loose soil since the lime nodules (if
any) might not be contained within a small amount
of loose soil. Look for soil lumps which have white
spots in it. (Refer Figure 12)
Place a small amount of soil in the Petridish.
Ground the soil into a loose form by hand. Do
not put water into the soil, since it will retard the
process of reaction with the acid.
After the required soil depth is reached collect
loose or lumps of the representative soil to be
tested. (Refer Figure 11)
Take water and mix with the soil to make it moist
enough to roll into a ball. Wait for a few minutes or
till all the soil has absorbed the water.
Use one hand to roll the moist into a ball. This
process might take a little bit time depending upon
the amount of water added. If the amount of water
added is accidentally more than that required then
take some more soil. Use fingers to smoothen and
uniformly mix the moisture with the soil.
Try to form the soil mixed with water into a smooth
16
GREEN BRICK MAKING MANUAL
Figure 12: Lemon Test for Determining
Suitability of Soil for Use in Brick Making
Take a small amount of acid by the pipette and put
over the soil. Watch closely for any effervescence
or bubbling action.
If the soil does not show any effervescent, repeat
the test with a separate soil sample.
After repeat tests, if the soil does not show any
effervescent, then it is free of lime. However, even
if there are minute cases of effervescence, the soil
contains lime nodules harmful for brick making.
3.4 Laboratory Tests
Chemical Analysis
Chemical composition of the soil is found out by
chemical analysis. Chemical analysis has been
one of the most reliable indicators to judge the
quality of soil suitable for VSBK. The important
chemicals to be analysed are Alumina, Silica, Iron
oxide, Calcium Oxide, Manganese oxide, Sodium
oxide and Potassium oxide. Our experience shows
that, Alumina, Iron and Magnesium has a very
significant role in defining the brick quality. If the
amount of Alumina is higher (range 20 to 30%) in
the soil, bricks have good ring, if the percentage of
Iron oxide is greater than 5%; it gives cherry red
color and Magnesium oxide gives the yellowness,
so generally less percentage of Magnesium (below
2%) is preferred for brick making in VSBK.
Chemical analysis of soil is carried out using
different methodology such as Furnace ignition,
Gravimetric analysis and Titrimetric analysis in
a well-equipped laboratory. It is not possible to
analyse the chemical composition of soil using
some practical methods at the site. However, a
person having the in depth knowledge in ceramic
can predict the compositions of major chemicals
by visually judging the soil and brick quality. (Refer
Table 1)
Table 1: Comparison of Chemical Analysis of Good and Ordinary Soil Sample for VSBK Firing
S No.
Test Parameters on Dry Basis
(% by mass)
Good sample
Ordinary
Sample
Method Use
1
Loss of Ignition
7.7
3.2
Furnace ignition
2
Silica as SiO2
61.8
80
Gravimetric
3
Iron as Fe2O3
3
0.9
AAS
4
Aluminum as Al2O3
23
14.6
Calculation
5
Sodium as Na2o
0.2
0.1
AAS
6
Potassium as K2O
2.76
Trace
AAS
7
Calcium as CaO
Trace
Trace
Titrimetric
8
Magnesium as MgO
1.2
1.2
Titrimetric
9
Organic Carbon as C
0.82
0.66
Titrimetric
GREEN BRICK MAKING MANUAL
17
VERTICAL SHAFT BRICK KILN
Mineralogical Analysis
Mineralogical analysis of soils gives a qualitative
data on the phases present. Determination of
phases is essential to know and predict the material
behaviour after reactions have taken place. The
mineralogical phases in soils are determined by
X-ray diffraction analysis. Generally before firing,
the following phases are present:

Illite (most common), Montmorillonite (present
in black soils), Kaolinite (white china clays)

Quartz (in the form of sand)

Muscovite, feldspar, haematite etc.
After firing with a mixture of soil, sand, and internal
fuel the following phases are developed within a
fired brick:

Mullite (needle like structure, gives strength)

Free quartz (gives fired strength)

Amorphous phase (glassy phase, acts as a
binding material)
Physical Analysis
Percentage of clay, silt and sand can be determined
by physical analysis. Similarly, plasticity index, liquid
limit and plastic limit of soil are also determined
18
GREEN BRICK MAKING MANUAL
Table 2: Properties of Good Brick Making Soil
Elements
Percentage
Clay
20 – 30
Clay & Silt
40 – 65
Liquid Limit
25 – 38
Plasticity Index
7 – 16
Volumetric shrinkage
15 – 25
by physical analysis. The properties of good brick
making soil are given in Table 2.
The given range of liquid limit, plasticity index and
volumetric shrinkage for producing good brick
quality has not yet been practically conformed. In
places where the physical parameters cannot be
analysed, one can even proceed to next step of soil
testing on the basis of chemical analysis.
Chapter 4
Choice of Brick
and Production
Options
4.1 Introduction
Many people may confuse clay brick with “brick”
made from other materials. For example, concrete
units rely on a cement paste to bond the materials
together. Moreover, concrete units are inherently
a grayish color, which means that users must inject
color pigments before the setting process and use
color sealant afterwards to have a color affect. On
the other hand, clay brick has thousands of color
and shade options that will not fade. Contrary to
some people’s perceptions, clay brick is actually
significantly stronger than concrete brick as well.
Another brick-like material, made from fly ash,
claims to meet the same performance standards
as clay brick.
Bricks are made from clay and shale – some of the
most abundant, natural materials on earth – and
then fired through a kiln at up to 1000 -1200º C. The
reason the brick turns into such a durable material
is that the clay/shale unit actually goes through a
vitrification process in the kiln, which enables the
clay particles to fuse together.

Concrete Bricks

Fly ash Clay Bricks
Common Burnt Clay Bricks
Clay bricks are man-made materials that are
widely used in building, civil engineering work and
landscape design. They are also used for paving
footpaths, sidewalks, driveways and garden beds.
Clay is a natural earth material with plastic
properties. It becomes cohesive when kneaded,
expands when wet, shrinks when dry and gains
strength when fired. The material can also be made
into various textures to complement the exterior
appearance of a home.
Common burnt clay bricks are formed by pressing
in molds. Then these bricks are dried and fired
in a kiln. Common burnt clay bricks are used in
4.2 Brick Types and Choice
Bricks are used for building and pavement all
throughout the world. In the USA brick was once
used as a pavement material, and now it is more
widely used as a decorative surface rather than a
roadway material. Bricks are usually laid flat and
are usually bonded forming a structure to increase
its stability and strength. There are several types of
bricks used many of them being about eight inches
long and four inches thick.
There are various types of bricks used in masonry.

Common Burnt Clay Bricks

Sand Lime Bricks (Calcium Silicate Bricks)

Engineering Bricks
Figure 13: Burnt Clay Bricks
GREEN BRICK MAKING MANUAL
19
VERTICAL SHAFT BRICK KILN
generalwork with no special attractive appearances.
When these bricks are used in walls, they require
plastering or rendering.
Sand Lime Bricks
Sand lime bricks are made by mixing sand, fly ash
and lime followed by a chemical process during wet
mixing. The mix is then moulded under pressure
forming the brick (Refer Figure 14). These bricks can
offer advantages over clay bricks such as:

Their color appearance is grey instead of the
regular reddish color
different colors as pigmented during its production.
Concrete blocks may be produced with hollow
centres to reduce weight or improve insulation. The
use of block work allows structures to be built in the
traditional masonry style with layers (or courses) of
staggered blocks. Blocks come in many sizes, blocks
are usually 390 mm × 190 mm × 190 mm excluding
mortar joints.
Fly Ash Clay Bricks
Predetermined quantity of fly ash is added to the
soil, depending upon the characteristics of the soil,
and thoroughly mixed when the mix attains proper
moisture content, casting of the bricks was done
manually and the moulded bricks were air dried.
Then bricks were placed in the kiln for firing at 900
± 10° C there after removed for use in building
construction.
4.3 Use of Internal Fuel in
Making of Green Bricks
Figure 14: Sand Lime Bricks

Their shape is uniform and presents a smoother
finish that doesn’t require plastering

These bricks offer excellent strength as a loadbearing member
Engineering Bricks
Engineering bricks are bricks manufactured at
extremely high temperatures, forming a dense and
strong brick, allowing the brick to limit strength and
water absorption.
Use of internal fuel in brick making is based on
the premise that substituting wastes into brick
making process either as fuels, pore opening or anti
shrinkage materials can improve the profitability
of brick making enterprises, reduce the working
hazards and also reduce the environmental impact
of brick making.
Many types of domestic, agricultural and industrial
wastes have an acceptable heat value and therefore
have a potential for use in domestic or industrial
processes that require heat. Some wastes. e.g.
boiler ash, slags, charcoal wastes, rice husks
can be clean burning and so less polluting than
conventional fuels such as coal or wood. Certain
industrial wastes acts as fluxes, thereby lowering
the firing temperature and hence the energy
Engineering bricks offer excellent load bearing
capacity damp-proof characteristics and chemical
resisting properties. These bricks satisfy the
minimum crushing strength and having a minimum
density of 1.9 kg/dm³, and have been fired to the
point of sintering, they count as engineering bricks.
Concrete Bricks
Concrete bricks are made from solid concrete.
Concrete bricks are usually placed in facades,
fences, and provide an excellent aesthetic presence.
These bricks can be manufactured to provide
20
GREEN BRICK MAKING MANUAL
Figure 15: Tobacco Dust as Internal Fuel
required to form the ceramic bonds in clay mixes.
This will obviously reduce fuel use and its associated
costs proportionally. The typical internal fuel that
can be used in Malawi is tobacco ash and boiler ash.
(Refer Figure 15)
Advantages of Using Internal Fuel
The compressive strength of bricks can be increased
by the addition of wastes that act as fluxes. If such
an increase is not required, the addition of a flux
may mean that, as an alternative, bricks can be
fired at a lower temperature, saving fuel while
maintaining acceptable properties.
heavy metal compounds found in some internal
fuels. Usually a fired brick can contain within
its structure these harmful substances without
significant leaching. Hence there is no risk to either
builders or users of these bricks. Brick making
therefore has potential of being the means of
disposal of heavy metals and harmful substances
which can otherwise find its way into human
consumption. Internal fuel use in brick making
can also reduce the suspended particulate matter
released into the atmosphere when coal is burnt
as an external fuel.
For more details on the internal fuel, refer to the
VSBK Operation Manual.
The density of common bricks is typically in the
range of 1.60 – 1.80 gm/cm3. When particulate
fuel is included in the bricks this burns away and
leaves pores. Thus the density of the final product
is reduced. On the other hand they are somewhat
less strong and durable. If density falls below
1.60 gm/cm3, bricks would not be durable enough
for use in construction.
Some types of internal fuel can cause the fired bricks
to change their colour. This is mainly caused due to
appreciable lime or iron content within the additive.
Alternatively, presence of iron also acts as a flux,
which decreases the vitrification temperature,
thereby decreasing energy consumption. For
internal fuel bricks, reduction in chemical reaction
occurs when insufficient air gets to the fuel. The
result is inefficient burning of bricks and the fuel
remains partly burnt. Also, during firing if bricks
are placed too close together in the kiln, black
reduction spots can occur where the surfaces are
in contact. Bricks with reduction cores and spots
are more likely to exhibit substandard properties
(Refer Figure 16 and 17). Often consumers do not
like the appearance and reluctant to buy the bricks.
Therefore firing of internal fuel bricks has to be
for a long period in a slow manner with increased
airflow. This problem is not supposed to occur
when the firing is done in a fixed chimney Bull’s
Trench Kiln. This is mainly due to its extremely slow
firing schedule with appreciable air flow through
the gaps between the brick setting.
In some cases, there is an interesting advantage
associated with internal fuel use in brick making.
Fired clay bricks can incorporate harmful or even
Figure 16: Black Core in Fired Bricks
Figure 17: Reduction Spots in Fired Red
Bricks
GREEN BRICK MAKING MANUAL
21
VERTICAL SHAFT BRICK KILN
Chapter 5
Green Brick
Production
Process
5.1 Introduction
Green brick production is the heart and science
of brick making. It is the most important aspect
in any and all type of brick making to achieve
quality and hence - profitability. Each step of the
entire green brick production system is interlinked
and is dependent on the earlier process. All
the process of green brick making are equally
important. Neglecting any one process will affect
the final product quality. The VSBK firing system
is a fast firing process with very little tolerances
for errors. Due to dynamic movement of the
entire brick columns and the load distribution on
each brick, the quality of the green brick must be
nearly perfect. However, this aspect of the VSBK
technology is never recognised, resulting in poor
brick quality. This has a direct effect on the fired
product resulting in deteriorating profits. This is
not understood by any brick producer thus putting
the entire blame on non-performance of the VSBK
technology.
Basic premise of VSBK technology
and its correlation with green
brick quality
GARBAGE IN = GARBAGE OUT
This chapter describes the best green brick
production practices with respect to manual
moulding and soft mud moulding with selective
mechanization. Heavy duty structural product
fabrication including stiff extrusion has not been
discussed here since they are not of economical
relevance with respect to Malawi brick production
scenario.
22
GREEN BRICK MAKING MANUAL
5.2 Necessary Conditions for
Green Brick Making
Malawi has abundant natural resources for making
bricks in the form of soil. Various types of soils are
found in Malawi for brick making. However for
sustainable brick production soil is not the only
raw material. The ultimate objective of any brick
production unit is its profitability and the presence
of an increasing market is the most important pre
requisite for establishing a brick production unit.
The minimum conditions needed to establish and
produce good quality green bricks are:

Soil

Additives

Water

Mixing

Ageing

Drying

Tools and equipments

Motivation

Space

Management
Soil
A brick production unit needs to have an acceptable
quality soil to produce a high strength green
brick. The better the green brick, better the fired
properties. Certain types of clay are not good for
brick making. For example soils with high sand
content have no plasticity and are difficult for
forming. After moulding these types of bricks will
deform on its own dead weight and are liable to
crack during handling. Similarly the soil used for
making pottery is not good for making bricks
because it has a high shrinkage rate which causes
the brick to crack during drying.
To select the proper soil for brick making, generally
select an area which has a tradition of brick making.
For non-brick making areas the soil from varying
areas and depths should be tested for suitability
in brick making.
The most important criteria for a go or no go are
the following:

Soil should not contain any lime

Soil should be free of large stone particles

Soil should be plastic i.e. it should retain its
formability
Additives
In green brick making additives are of the following
types:

Internal fuel

Anti-shrinkage material

Structure opening material
Internal Fuel
For firing of green bricks in VSBK in an energy
efficient manner, addition of internal fuel is an
absolute necessity. Without internal fuel content,
firing of green bricks in a VSBK is not recommended.
Internal fuel not only reduces the external fuel
consumption but also saves on the emission
thereby reducing pollution.
Internal fuel is a waste materials produced by
process industries. The various types of internal
fuel suitable for Malawi include:

Tobacco industry waste

Boiler ash from sugar industries

Textile industry sludge

Coal dust of inferior quality

Distillery industry waste

Agro industry waste
These wastes are usually dumped by the industries
and are mostly available free of cost. It is mixed
with the soil during its dry mixing process. Quantity
of addition depends on the quality of the soil and
the internal fuel.
Anti-shrinkage Material
To make highly plastic soils suitable for brick
making anti shrinkage materials are added. This is
to avoid high shrinkage and resultant cracks during
drying in the open atmosphere. Depending upon
the availability the following types of anti-shrinkage
materials can be added:

Boiler ash

Fine sand

Stone dust

Sandy soil
Before addition refer to an expert for determining
the quantity to be added. Too much addition might
affect the fired brick property.
Structure Opening Material
In areas of very low humidity and high temperature
e.g. summer months in Malawi, a structure opening
material should be used in green brick making.
This is sometimes in addition to as anti-shrinkage
material also. The materials generally used are:

Rice husk

Wheat straw

Saw dust
These types of materials are used only during the
summer months. They are used within the green
brick to delay the shrinkage rate of green bricks
during drying. These type of materials are added
to a maximum of 2% only depending upon the
plasticity of the soil. Too much addition reduces
the property of the fired brick.
Water
One of the most important raw materials for
making bricks is water. To produce bricks one must
have sufficient quantity of water available. Before
starting a brick production unit, a continuous
source of water supply must be determined.
GREEN BRICK MAKING MANUAL
23
VERTICAL SHAFT BRICK KILN
Generally for brick production water is supplied
from own submersible water pumps, or deep wells.
Check the water level for the availability of water
during the summer season also.
To produce 1,000 bricks approximately 750 litres
of water is needed during moulding only. Apart
from water source and lifting, proper distribution
system needs to be established so that it reaches to
moulder in appropriate time and quantity.
Mixing
An important criterion to produce good green bricks
is that all the raw materials including additives,
soil and water should be mixed thoroughly.
Aggregation of any single material within a green
brick is a source of weak spot thereby reducing its
fired property.
Usually mixing is done manually by moulders.
However if proper supervision is not there often
the mixing is not done properly. It is always
recommended to adopt a mechanized means of
mixing e.g. by pugmill. This will not only ensure
uniformity of the materials but also a greater
compacted material will less water content, which
is good for achieving quality. For mechanized brick
making through soft mud moulding technique to
extrusion, mixing is completed within the process.
Ageing
The process of ageing uniformly dissolves the
dry particles of soil and develops plasticity within
the soil. Uniformly plastic soil makes bricks of
uniform quality.
The process and time of ageing depends on the
quality of the soil and may vary from 24 hours to
several days. The longer the time, the better the
ageing. Always remember that ageing should be
done under moist and warm conditions. Higher
temperature helps in speeding up the ageing
process.
Drying
Proper use of dry green bricks is essential to
achieve good fired quality. Before transportation
or stocking of green bricks it has to be ensured that
the green bricks are fully dry.
To achieve this proper stacking of bricks is a
necessary prerequisite. The rate of drying or drying
time depends upon the plasticity of the soil and
the atmospheric conditions. Higher plasticity soil
will take more time for drying than sandy soils.
24
GREEN BRICK MAKING MANUAL
Similarly the same quality of green bricks will dry
much faster during the summer time compared to
the winter time. Generally in hot areas with very low
humidity (30% - 40%) green bricks get fully dried
within 4–5 days. Whereas the same bricks during
winter time will always contain moisture of 6% 10% even after 21 days.
Tools and Equipment
A brick making unit needs basic tools in order
to make green bricks. For a two shaft VSBK unit
requiring approximately 10,000 bricks per day will
need a family of 10-12 moulders depending on their
productivity. The following minimum equipments
will be needed for smooth production:

1 pugmill

6 pick axes

12 spades

12 wheelbarrows

4 levelling rings

12 brooms

2 cft box

24 moulds

12 bowcutters
Space
Sufficient space is needed for moulding and
drying bricks. The site should be hard, smooth,
clean and leveled. During the winter months more
space is needed due to longer drying time whereas
proportionately lesser time is required in the summer
months.
To accommodate 12 moulder family will need an area
of approximately 9,000 sq.m.
Motivation
The production of handmade bricks is exhausting,
tedious and dirty work. Therefore, in order for a brick
production unit to succeed, the workers must be
motivated towards their want to produce the bricks.
A cordial atmosphere of give-and-take should be tried
and installed amongst the work force. They need to
feel that the making of good green bricks will benefit
them by earning a living through an increased profit
from surplus generated in the business.
Management
As with any production unit or business, good
management is the key to a successful brick
business. Unfortunately this aspect is often ignored
or forgotten because brick making is considered
to be a “low” or relatively simple technology. It has
to be remembered that a brick production unit
cannot withstand more setbacks than a normal
commercial business.
Management of a brick unit means planning,
organizing, staffing and controlling the production
in order that the bricks can be produced within
budget and sold profitably. This has to be ensured
through

Quality

Strength
Benefits of Standardisation
Many builders and contractors do not like to use
bricks from small time producers like clamps since
the bricks can vary a great deal in form, size, colour
and quality. For example one clamp owner may make
a brick of 200 mm x 100 mm x 60 mm and another
in the same area may make a brick 220 mm x 100
mm x 68 mm. Because the sizes differ, it is difficult
for a builder to mix these bricks when building a
wall. A large contractor may need 20,00,000 bricks
annually, yet many small clamp owners may produce
on 1,00,000 bricks per season. Thus if he purchases
bricks from 20 different producers making 10
different sizes and quality it would cause problems
for construction.

Adequate and timely supplies of raw material

Maintenance of equipment

Suitable production facilities for workers, their
safety and comfort

Quality control of raw material, process and
finished product

Smooth flow of production

Adequate financial arrangements for wages and
general purchases

Good book keeping system

Suitable recruitment and training of skilled
personnel

Specific tasks and roles for each staff
There are three general types of brick forms:

Skill upgradation

Hollow blocks

Good human behaviour

Solid extruded bricks

Solid hand moulded bricks
5.3 Standardisation of Green Bricks
Standardisation of green bricks is necessary to
deliver into the market a uniform quality of fired
brick. This is necessary since in a VSBK the shaft
size is decided based on the green brick size and
cannot be changed afterwards.
The characteristics of standardisation are based on

Form

Size
Another advantage of standardising the bricks is being
able to accurately calculate the number of bricks
needed to construct a building. It also means that the
size of the openings (e.g. doors and windows) can be
calculated and can be made before the building is
completed. Standardised bricks also save cement due
to lesser amount of plastering and mortar joints.
For standard brick size refer to Malawian Standard
codes. The standard brick dimension as stated is 230
mm x 110 mm x 75 mm.
Characteristics of Standardisation
Form
Hollow Blocks
Normally these types of blocks are made in a large
brick factory with special machines and equipment.
In rural areas it is also possible to make hollow blocks
with special wooden moulds, but the results are often
unsatisfactory.
Builders often like using hollow blocks because the
larger size allows them to build a house in less time
than with smaller solid bricks. The only disadvantage
is that they do not have any frogs (depression
in bricks).
GREEN BRICK MAKING MANUAL
25
VERTICAL SHAFT BRICK KILN
Solid Extruded Bricks
Although these bricks are widely used in South
Africa, they are slowly gaining prominence in the
rest of Africa. They are also made with expensive
machines and infrastructure. These bricks generally
have high strength. They are generally used in
special construction areas with exposed brick work.
However these bricks are not gaining popularity due
to the following
Length
There is a very important relationship between the
length of a brick and its width because of the way
we follow brick laying.

Do not possess frog

High cost of extruded machine
The length of a brick should be equal to twice its
width plus 10 mm (for the mortar joint). A brick with
this length will be easier to build with because it will
provide an even surface on both sides of the wall.

High infrastructure development
Height

Cannot dry in the open atmosphere

Specialised firing techniques
The height of a brick, though of less importance
also has a relationship with the length of the brick.
The height of three bricks plus two 10 mm mortar
joint should be equal to the length of the brick. But
nowhere this relation is followed.
Solid Hand Moulded Bricks
Solid bricks are most commonly manufactured
by both big and small clamp owners and VSBK
entrepreneurs. They have the following advantages:

The form is simple. It is much easier to make the
mould and easier to mould the brick
Generally the height varies according to tradition
and the firing practice. In clamp kilns the height
varies between 50 mm to 70 mm. In a VSBK firing
system best results in terms of quality and energy
consumption are obtained with green brick height
between 70 mm to 75 mm.

They can be fired in all types of kilns
Minimum and Maximum Dimensions

The bricks have good strength and can be used
also as a load bearing structure.

They can be used to build arches

If the bricks are made and fired properly, it is
not necessary to plaster the wall, thus saving on
construction costs
Each fired brick made by ordinary hand moulding
process will never be exactly the same size. They will
vary due to mixing process, water content during
moulding, compaction style and size of moulds.
Whereas these variations are unavoidable, they
should be limited within a range.
Size
A brick has a length, width and height. The size or
dimensions of a brick are determined by how it will
be used in construction.
Width
The width of a brick should be small enough to allow
a mason to lift the brick with one hand and place
it on a bed of mortar. For an average mason, the
width should not be more than 115 mm. If the brick
was wider, the mason would have to put down the
trowel while building the wall to pick up the brick
by two hands. As a result time would be wasted.
In addition, a wider brick would weigh more and
26
therefore tire the mason more quickly. In terms of
production, a larger brick is more difficult to fire in a
kiln and consumes more energy for the same price
realization.
GREEN BRICK MAKING MANUAL
Ideally bricks manufactured by any process should
have dimensional tolerances of 2%. This means that
if the brick size is 230 mm x 110 mm x 70 mm, the
length of the brick should be between 226 mm and
234 mm. The width should be between 108 mm to
112 mm and the height between 69 mm to 71 mm.
Quality
A good quality brick should be regular in shape and
size, with smooth even sides and with no cracks or
defects.
Normally poor quality bricks are a result of poor
soil selection or as a result of poor techniques when
making the bricks. However these errors can easily
be overcome.
Strength
5.4 Stages of Green Brick Making
Bricks must have enough strength to carry the
weight of the roof. If bricks are well made and well
fired, there will be a metallic sound or ring when
they are knocked together. If they make a dull
sound, it could mean that the soil is improper or
they are either cracked or underfired.
Table 3: Shrinkage Rates and Mould Sizes
Fired Brick Size: 230mm x 110mm x 70mm
Shrinkage
Rate
A simple test for strength is to drop a brick from
a height of 1m (shoulder height) horizontally on
a hard floor. A good brick will not break. This test
should be repeated with a wet brick (a brick soaked
in water for 7 days). If the soaked brick does not
break when dropped, the quality is good enough
to be used in construction. If the bricks dissolve or
fall apart underwater or during handling, the bricks
were probably underfired or too sandy.
Mortar Joint
Brick mortar can be made form lime, cement or
mud. Generally in urban areas cement is used
whereas mud masonry is used in rural villages. The
purpose of mortar is to join the bricks together in a
fixed position and to smooth out the irregularities
in the shape and size of the bricks. This is necessary
in order to transmit the load or weight correctly and
evenly throughout every part of the wall.
The strength of the mortar should be less than
that of the brick. This will prevent the bricks from
cracking when a wall or a foundation settles. If
movement does occur, it is better to have the
mortar crack instead of the brick because it is easier
to repair or replace mortar than a brick.
The strength of a wall is also affected by the
thickness of the mortar joints. A 20 to 30 mm sandcement mortar joint is much weaker than a joint of
10 mm. For a strong wall, all mortar joints should
be 10 mm thick.
Moulds
All good brick making material will shrink when
dried and fired. Generally the shrinkage is higher
in the green stage. During firing it is nominal to
negligible. Thus the brick making moulds should
be larger than the final size of the brick. Good brick
making soils have shrinkage between 5% - 10% and
therefore the moulds should be 5% - 10% larger
than the fired brick size. It is extremely essential to
accurately calculate the shrinkage rate of the soil
under various temperatures and heating schedules
for finally determining the mould size. This has to be
done in a laboratory or by a ceramic expert. (Refer
Table 3)
Interior Mould Dimensions
Length
Width
Height
5%
241
mm
115
mm
73 mm
6%
244
mm
117
mm
74 mm
7%
246
mm
118
mm
75 mm
8%
248
mm
119
mm
76 mm
9%
251
mm
120
mm
76 mm
10%
253
mm
121
mm
77 mm
There are six main stages of green brick making
before they go for firing. They are:

Extraction of clay

Soil preparation


Grinding
Soil processing

Manual mixing

Pugmilling

Filtration

Moulding

Drying

Stacking
Within each of these stages there are several
important steps. Each one of them is important on
GREEN BRICK MAKING MANUAL
27
VERTICAL SHAFT BRICK KILN
its own right and is complimentary to each other
towards achieving the ultimate product – a good
green brick.
Equipments

Shovels
Each of the steps has been discussed in more
detail in subsequently.

Broom

Pick axes

Wheel barrows

Tractor
Extraction of Clay
Before the start brick production the search for
a good clay deposit should be over. Not only the
quality but the availability of it for atleast 5 years
must be ensured. Once the source of soil has
been located and properly tested in laboratory
the process of extraction starts.
The first step is to cut the grass and any short
bushes. (Never select an area which has a high
concentration of big trees. They are very difficult
to cut and are not possible to take out the roots.)
Clean the area from any other foreign matter like
roots, vegetation, dry leaves, and stones.
When the area is cleaned, approximately 6
inches of the top soil should be removed for
use in agriculture. The depth will vary until one
encounters clear soil.
After removing the top soil, the digging and
transportation of dry soil begins. The soil should
be dug to atleast to a depth of 6 ft or till one
encounter good soil whichever is lesser. During
digging soil should be taken out vertically and
not horizontally. This is necessary since one
encounters more plastic soil as depth increases.
This might not be true always. Before digging
of actual soil for brick making commences one
should make an assessment of the soil quality
based on vertical and horizontal digging.
Whenever one encounters a sandy layer digging
of soil should be discontinued.
The soil can be prepared in situ at the digging site
or can be transported based on the requirement
and site conditions. If the moulding site is far
away from the firing area and the soil quality
is appreciably good then it is profitable to
transport the green bricks instead of soil. In a
100 cft capacity tractor the soil transported will
be enough to make only 800 bricks. However
in the same tractor one can transport at least
2000 of dried green bricks. Thus transportation
of dried green bricks saves on expenses. The
only disadvantage is that if the green bricks are
not of good quality then it will incur appreciable
transportation breakage.
28
GREEN BRICK MAKING MANUAL
Soil Preparation
Grinding
In Malawi a majority of the brick making soils
available are usually coarser in variety. Although
the most widely used are the black soils, throughout
the country occurrences of red colour granular soils
are prolific. In presently followed practices, these
soils are usually dug out and formed into bricks.
Presence of coarser particles induces cracking
shrinkage due to these coarser particles.
These kind of coarse texture soils should be ground
into smaller sizes to create more surface areas
for higher degree of plasticity. There are various
industrial scale crushers and grinders available for
size reduction of coarse soils. The most common
equipment’s are jaw crusher, roller crushers,
disintegrators and pulverizers in order of decreasing
fineness. Choice of crushing equipment’s is usually
left to the process engineering part of the brick
production system comparable with the economics
of brick production.
The most suitable and low cost equipment for
crushing of coarser particles are the disintegrators.
These are quite inexpensive and can be fabricated
and maintained locally. The only issue is the
maintenance of the impact blades and the sieve.
This issue can also be solved with choice of
hardened steel materials.
The only disadvantage of using disintegrators is
that the soil has to be dry. Use of moist soil will
choke the openings of the sieve and retard the
productivity process.
Soil Processing
To make good quality green bricks, the dry/moist
lumpy clay has to be properly mixed with additives
into a uniform, smooth and soft moist mixture
containing no hard lumps of soil or stones. It should
not be too soft or too hard and should have enough
plasticity for shaping and retaining the form.
To obtain this mixture, the soil is treated in four
different steps:

Batching and addition of additives

Dry mixing

Ageing

Wet mixing
Keeping the basic steps same the process of soil
preparation varies depending upon the general
practice followed in various regions. Mostly they can
be classified broadly into four different categories:

Manual mixing

Semi-mechanised mixing

Filtration techniques

Other mixing techniques
Internal fuel is added depending on its quality, soil
characteristics and external fuel consumption.
Convert the internal fuel and other additives
from weight to volume basis. For this you need to
construct a cft box. It is a wooden box having internal
dimensions 1ft x 1ft x 1ft. It also has two handles on
two ends for easy handling and transportation.
Convert the material to be added from weight into
volume.
1
2
3
4
5
6
Each of the process has been discussed in greater
detail below.
Manual Mixing
To make good quality green bricks, the dry lumpy
soil has to be mixed uniformly with additives and
then turned into a smooth, soft paste.
Batching and Additives
After digging or transporting the soil, it is spread
evenly over the mixing area. The lesser the pile
height, the better the mixing in lesser time. Take
eight fired bricks from your area. Around the soil
pile keep them in an octagonal pattern on the
height. Thus the height of the soil pile can now
be measured to one brick length. Spread the soil
evenly to this brick height. You will require to move
the bricks to widen the pile. The dummy bricks can
now be taken out. Always perform this step before
adding other materials.
Sieve the additives in a 2 mm mesh before mixing.
However the rice husk if added does not require
any sieving since it is of uniform size. Keep aside
the sieved material that passed through the 2 mm
mesh. Sieving is of utmost importance since any
particles bigger than 2 mm will make the fired brick
weak due to absence of any binding with the soil
matrix.
Depending on soil plasticity, anti-shrinkage materials
like stone dust, fine sand, boiler ash are added.
Figure 18: Manual Mixing Process
Add one material at a time. Preferably the low
density materials should be added first i.e. internal
fuel and then stone dust. For all purposes, rice husk
to be added at the last. The material to be added
should be spread uniformly over the pile. If in any
place there is a cluster of additives spread uniformly
over the soil by hand. Repeat the process similarly
for other additives.
Dry Mixing
After the materials are added, the pile should be
dry mixed at least two times. Dry mixing should be
started from one end only. Never start dry mixing
from two ends by two persons. For dry mixing
use a spade have a blade length of more than 9
inches. This will ensure that during cutting the blade
GREEN BRICK MAKING MANUAL
29
VERTICAL SHAFT BRICK KILN
reaches the bottom. Always make a small and deep
cut. If the first cut does not reaches the bottom,
then next time again cut it to reach the bottom.
Never try another area. Remember that best mixing
is achieved by cutting vertically and not horizontally.
After the whole pile is mixed, repeat the process
again. During the cutting process break any big
lumps of soil into small pieces. Take out any roots
or organic matter. Reject all stony particles. Ideal dry
mixing can be judged by the uniformity of colour of
the pile
After proper mixing again, spread the mixed pile
uniformly having a brick height. Start the flow of
water from temporary channels. Remember that the
water flow should be slow to allow the soil to absorb
water. Never force the water on the soil. Generally
there are no methods of controlling the quantity
of water. It is best to leave it to the jurisdiction of
the moulders. However, best bricks are made with
low water content. Generally 20% - 25% by weight
of soil, water is added. However this depends on
the soil quality. Sandy soils require lesser water,
whereas clayey soil needs more water.
Ageing
After the mixed soil and additives has been watered
it is very important to see that the whole mix is aged
properly. Ageing is the process of adding water to
the soil and allowing it to stand undisturbed for a
few days before mixing. This process enables the
soil lumps to soften and break into smaller pieces
making the mixing process easier. Technically water
enters the clay particles and enhances the plasticity
of the mix. Plasticity ensures good shape, size and
finishing of green bricks.
For ageing in manual mixing generally the process
followed is to allow the water to stand with the soil.
For proper ageing of the soil the following needs to
be ensured:
30

The whole soil pile is covered with water

Too much water is not on the pile

The water does not evaporate during the ageing
process. If need arises then the pile needs to be
covered with a black plastic.

The longer the ageing process the better the
soil properties. However to have a judicious mix
of property and productivity the ideal time of
ageing has to be atleast for 72 hours.
GREEN BRICK MAKING MANUAL
Wet Mixing
After the soil and additives has been aged well, it
needs to be mixed and kneaded. The purpose of
mixing is to ensure that the soil mix is a smooth,
soft and homogenous mixture containing no hard
lumps.
There are various methods of mixing aged clay for
small scale brick making. One can use a machine or
do it manually. Semi mechanised mixing process
has been described later. The main problem with
this type of process is that it requires a 3-phase
electricity connection for operation. In remote
areas installation of electrical connection is costly.
Moreover supply of the same is also erratic.
Thus, the most preferred mixing process is
manual – trampling by feet. The aged clay is
spread out where moulders trample it with their
feet until it becomes a smooth mixture with a
uniform colour. One advantage of this system
is that rocks, stones, vegetation can be felt with
the feet and removed. The main disadvantages
are that uniform mixing is not possible. Sincere
workers will ensure a smoother mixture. Another
difficulty is that it is inhumane and tiring.
Moulders daily have to spend atleast 1-2 hour for
ensuring smooth mix. At times this type of mixing
process can be hazardous also. If there are any
sharp objects within the soil e.g. nails, metal parts,
pieces of glass or rough stones the moulders are
likely to get hurt. Thus wherever possible this type
of mixing process should be avoided.
Semi-mechanised Mixing
In this type of mixing the quantity and process
has been optimized for a two shaft VSBK requiring
around 10,000 – 12,000 green bricks per day.
This type of mixing process has the advantage
of ensuring uniform quality of aged and mixed
soil to the moulders. It ensures uniform quality
of green bricks. Although the processing requires
greater manpower its ultimate profitability is the
reduction of breakage and better fired product.
Batching and additives
During semi-mechanized mixing, since the whole
processing of soil takes place at a time so it
makes more sense to transport the soil in an area
nearer to the mixing machine. Soil needs to be
transported in tractors. After removal of the top
soil the digging and transporting the dry clay soil
has to be done to the transporting area.
After one tractor load of soil has been transported
and dumped the required amount of additives has
to be spread uniformly over the whole pile.
Depending upon the green brick weight one tractor
load of soil will produce approximately 1000 – 1200
green bricks. Thus to produce 10,000 green bricks
approximately 10 tractor loads of soil is required
each day.
The second tractor load of soil has to be unloaded
over the previous pile only. Do not unload away
from the pile. The same process of additives
spreading has to be adopted. This type of unloading
in piles has to be followed till the required soil has
been transported.
For ensuring smooth production, three number of
piles are needed. The first pile will be used after 72
hours of ageing and mixing. All the piles has to be
placed in a semi circular fashion around the mixing
machine so that the transportation time from the
pile to the pugmill is minimized.
the machine appropriate layout of the process and
its management is necessary.
Filtration Techniques
This type of mixing process is generally followed
in areas where the soil contains a large amount
of lime and stone granules. It is impracticable to
invest in grinding machines since it is out of the
reach of small brick makers. On the other hand it
is necessary to separate the granules for arresting
cracks within the green bricks and make it amenable
to moulding.
The main disadvantages of this process are that
it requires a large amount of water and is time
consuming. Additionally it takes up a large land for
processing and is suitable only for very small brick
makers who operate intermittent clamp kilns.
The quality of soil is excellent and addition of nonplastic material is an absolute necessity to reduce
the plasticity and prevent shrinkage cracks.
Dry Mixing
Filtration of Soil
After the required soils and additives had been
added the pile has to be cut and mixed in the dry
state at least twice. The process described earlier
has to be followed.
Generally the soil is transported in tractors and
dumped near the filtration machine. The filtration
machine consists of a drum with a paddle stirrer
attached at the central part. The top part is open
to accommodate the soil and water. At the bottom
there is an outlet for the slurry to drain out.
Watering and Ageing
For ageing the same process described earlier has
to be followed.
Pugmilling
After the required ageing is completed the aged soil
is put into a mixing machine – the pugmill.
The pugmill is a simple mechanical mixer operated
through a 7.5 HP electrical motor or a 10 HP diesel
engine. It is cylindrical 10 mm thick MS sheet drum
of approximately 200 – 250 litre capacity. It has a
central shaft to which paddle blades are fixed at
various positions. Soil is fed from the top and taken
out from the bottom. Uniform mixing of the soil is
due to its churning inside the drum at various stages
and forcing out the mixed soil through the bottom
by the paddles. The uniformity of the mix is judged
by the homogenous colour. It operates through a
gear and pinion system and speed can be varied
for faster output.
It is a continuous process having an output
of 12,000 – 15,000 bricks per day. It has to be
remembered that to get the optimum output from
Soil is fed from the top into the drum. Sufficient
water is added to dissolve the soil. The paddle is
rotated through a motor to agitate the soil-water
mix and break down any soil lumps. Coarser soil
lumps are also dissolved in this action.
After the soil is fully dissolved in water which usually
takes around 30 – 45 minutes, it is drained out over
an 1mm MS sieve. The coarser particles are taken
out while the soil mix is drained out to storage bins
through channels made for drainage. Usually the
filtration machine is placed on an elevation to take
advantage of the natural drainage system.
Storage and Additives
For storage of the soil slurry, the most economical
means is to dig pits and store in them. Usually this
is the process followed. Ideally the pits should be as
shallow as possible to facilitate evaporation.
The dimension of the pits should be 20 ft x 10ft
x 1 ft. The depth should not be more since it
will be difficult for people to mix the slurry with
additives. Each pit is sufficient to mould atleast
GREEN BRICK MAKING MANUAL
31
VERTICAL SHAFT BRICK KILN
2000 bricks serving two moulder families. Thus
to mould 12,000 bricks per day 6 numbers of pits
are required. During the summer months it takes
approximately 4 days for the slurry in the pit to dry
enough for amenable to moulding. Thus to ensure
uninterrupted production there should be atleast
24 pits. The pits usually are dug in the ground. This
facilitates evaporation of water from the surface
and soaking from the bottom.
After the pits are filled with soil slurry, required
additives are spread uniformly over it. The internal
fuel quantity is the same as during other moulding
process. However to decrease the plasticity and
reduce shrinkage cracks approximately 20%-30%
by weight of stone dust or fine sand is added. In
addition fly ash, bottom ash or boiler ash from
thermal power plants are also added between
the range of 10% - 30% as filler materials. These
materials not only reduce the plasticity but
increase the green and fired strength of the bricks.
Additionally it reduces the consumption of external
fuel during firing also.
Rotovator
This is a simple rotating attachment fixed at the
back of a tractor. (Refer Figure 19)
In this process for required mixing a large shallow
pit is made on the ground. The pit dimension is
approximately 100 ft x 100 ft having a depth of not
more than 1 ft. Soil is transported and dumped in
the pit uniformly. After required levelling additives
are measured and spread uniformly over the soil
layer. Care is taken to see that the soil-additive layer
is not more than 6 – 9 inches at any place. Water is
added in sufficient quantity to make the soil wet.
In this process generally more water is added than
Wet Mixing and Ageing
After the additives are spread out evenly over the
slurry pits, it is churned in the watery state in the
pit with the help of wooden or metal ladles. This
ensures a very good mixing of the soil and the
additives which gives a uniform firing property and
strength.
The mixed soil is left to dry out naturally for atleast
3 to 4 days in the pit. Apart from drying good ageing
also takes place. This further increases the plasticity
of the soil.
Generally by around 3 to 4 days the mixed soil
becomes ready for moulding. However this time
depends on the weather conditions. In winter
season this time even extends beyond 7days.
During this phase the mixed soil is taken out from
the respective pits and left at the surface for further
drying. The empty pit is further used for another
batch of soil slurry.
Other Mixing Techniques
Apart from the above three most commonly
followed soil preparation techniques, in some
parts of Asia local indigenous mixing techniques
have also been evolved due to an enterprising,
innovative mentality by progressive entrepreneurs
and can be innovatively adated in Malawi also.
A short description of some of them has been
attempted in the following sections.
32
GREEN BRICK MAKING MANUAL
Figure 19: Rotovator
required for moulding. This soil mixed with water
is left to age in the shallow pit for atleast 48 – 72
hours.
After required ageing, the tractor is moved around
the soil in circles. Initially it is made to rotate on
the outer layer in a circular fashion. Gradually the
circle is made smaller so that the soil all around is
mixed uniformly. At any given time the central part
is not mixed at all since the tractor cannot make
the round at that place. After uniform mixing the
soil is transported by respective moulders for green
brick making.
The advantages of this process are that a large
quantity of soil can be mixed at a time. Moreover
the total mixing time is only about 2-4 hours and it
requires no labour. However one has to invest on
an expensive tractor for this work although it can
be used for carrying fired bricks. The soil mixing
quality is also not upto the mark and often it gives
rise to inconsistent fired brick quality.
Wet Mixing
In this process a deep pit is dug in the ground
approximately to a depth of 3 – 4 ft. The pit is filled
with soil at the first instance. Required additives are
uniform mixing quality since small particles of
unmixed particles still remain within the soil mix.
Moulding
Figure 20: Wet Mixing
spread out over the soil and dry mixed thoroughly.
The main difference with other processes is that
the water added is of large quantity. The whole pit
is flooded with water so that the mix is fully under
water. After required ageing for atleast 24 – 48
hours it is mixed manually. (Refer Figure 20)
The mixing is usually done by hand. The moulder
steps down into the pit with naked feet and
tramples the soil mix. During this process the hand
is also used to break soil lumps and take out any
hard or solid particles like stone, roots etc. It is
generally believed that the right depth of the soil
mix is judged by the fact that the nose of the bend
moulder during mixing should remain just above
the water.
This is generally an effective way of mixing but quite
laborious and is possible where water is available
in plenty.
Paddle Mixing
This type of mixing is the same as manual mixing
process. The main difference is in the wet mixing
methodology. Unlike manual mixing excess amount
of water is added into the dry mix and left to age
for the required time. After tempering the wet soil
mix is spread into a very thin layer. The height of
the layer is never more than 6 inches. Four to five
persons jointly trample the soil in a watery state.
The trample style is very much different than the
ordinary manual process. The steps are very small
ensuring uniform mixing.
This type of mixing is extremely time consuming
and tedious. It is also hazardous since moulders
might damage their feet from presence of sharp
objects. However the quality of the mixed soil is
much better than the ordinary manual process.
Still even through this process one cannot achieve
Moulding is the process by which the prepared soil
is formed into the shape of a brick. There are two
methods of moulding; manual and mechanized.
Manual process consists of slop moulding and sand
moulding. Mechanized moulding consists of semi
mechanized pressing and low cost extrusion. Apart
from these there are more sophisticated methods
of brick making e.g. mechanical pressing, hydraulic
pressing and stiff extrusion. The latter methods are
out of the scope of discussion since they are out
of bounds for small scale brick makers due to its
extremely high investment cost.
Figure 21: Slop Moulding
Slop Moulding
Slop moulding is the most traditional method of
brick making. The brick is formed in a rectangular
wooden or metal mould which has no bottom or
top. The mould is wetted and placed on the ground
and filled with a very wet soil-additives mixture.
Palm of the hand is used to remove the excess soil
and smooth the top of the brick. The mould is then
lifted off, leaving the brick on the ground to dry.
(Refer Figure 22)
Often this method produces poor quality bricks
because of the excess water used both in the
mixing of the soil and the wetting of the mould. The
soil mixture becomes so wet and soft that the newly
made brick begins to deform under its own weight.
It takes the shape of the ground on which it is laid.
Once placed on the ground, it cannot be moved
because it is so soft. Often the brick is marked or
deformed if accidentally touched or moved the
GREEN BRICK MAKING MANUAL
33
VERTICAL SHAFT BRICK KILN
brick dries properly. The excess water can also
cause the brick to crack and break during drying.
Sand Moulding
Sand moulding is a drier method of shaping
bricks. If proper care is taken during moulding
it can be comparable even with machine made
bricks.
Sand moulding uses a drier stiffer soil mixture
compared to slop moulding. The soil is formed
into a wedge shape and all its sides are covered
with a “releasing agent” which prevents the soil
from sticking to the sides of the mould. The most
common releasing agent is fine, red burning
sand and hence the term “sand moulding”.
However, in some areas other type of releasing
agent e.g. saw dust, brick dust, coal dust and
even fly ash is used as a releasing agent. The
soil wedge, covered with releasing agent, is
thrown with force into a simple mould open
at only one end. Rather than use hand to level
off the top of the mould, a “bow cutter” is used
to remove the excess soil from the mould. The
mould is overturned and taken out vertically
to slide out the newly formed green brick on
the ground.
Demoulding yard
Quantity of Water
Adding the correct amount of water during soil
preparation is critical for making good quality
bricks. The lesser amount of water used, the
better the quality. The best quality green bricks
are made by hydraulic presses where the amount
of water is only around 2-4%. Amount of water
also depends on the soil quality. Generally sandy,
silty soils will require lesser water than clayey
plastic soils. However actually in practice the
amount of water depends entirely on the habit
of moulders. Soil with higher amount of water
is easier to mould than those with lesser water.
Close supervision is necessary to control the
habit of adding more water with moulders.
If there is too much water in the soil, the green
brick will:

Deform easily under its own weight after
moulding (true in cases of sandy and silty non
plastic soils)

Deform when placed on uneven or bumpy
ground
Because the soil to make the brick has
appreciably less amount of water compared
to slop moulding, the moulded brick is much
harder. However it is not possible to handle
the bricks before 24 hours of drying. Since the
bricks are hard they do not deform easily due to
its own weight. They also dry faster with much
less cracking and breakage.

Have higher and inconsistent shrinkage

Crack during drying especially in the summer
months

Take much more time to dry
It has to be remembered that all the above
advantages depends on the soil property. Non
plastic, sandy or silty soil is not good for this
type of moulding and all the merits of sand
moulding are nullified.

Productivity will be less since it will take more
time for moulders to mould bricks

Finishing will not be perfect since the soil may
not flow into the corners of the mould during
throwing the wedge

Presence of layer cracks
The whole sand moulding process can be
broadly classified into seven steps. They are:
34


Quantity of water

Making and throwing the wedge

Releasing agent

The mould

Cleaning tools

Bow cutter
GREEN BRICK MAKING MANUAL
If there is too less water in the soil:
Generally the optimum amount of water in soils
should range between 20% - 25% by weight.
Sandy and silty soils will require lesser water
whereas clayey soils will require more water.
There is a simple test that can be done to check
if the soil has the correct amount of water. A
wedge should be made out of the moulding soil
manually and it should be vertically kept on a
hard ground with the narrow edge down. If the
wedge does not change its shape, the amount of
water is correct. If the wedge begins to deform,
there is too much water in the soil mix.
If the soil mix is too wet and soft then, non plastic
materials or even soil mix can be added uniformly.
If this process is not practically feasible then just
spread the soil mix in thin layer and allow it to
dry until it reaches the correct moisture content
and stiffness. However before using the soil, the
pile has to be mixed uniformly since during the
drying process the top layer will be drier than the
bottom of the spread out pile. Uniform mixing of
uneven dried soil is necessary to achieve optimum
quality.
Making and Throwing the Wedge
Usually during moulding, moulder for convenience
sake stores a considerable amount of processed
soil. Moulder is usually not a single individual but a
family of two. In South Asia generally partnership
is between husband and wife. It can even be
done individually. Distinct roles and activities are
determined and followed.
One member usually carves out a measured (by
practice and experience) quantity of soil mix from
the heap and rolls over the releasing agent before
passing over to moulder.
The throwing wedge is formed with the ball of
soil mix rolled over the releasing agent. The
wedge is a triangular shape of soil having length
slightly shorter than the mould length. When the
wedge has been coated evenly with the releasing
agent, it is thrown into the mould with force. To
generate a natural force it is usually thrown from
approximately a height of 1ft above the mould.
The art of good moulding is the angle and force of
throwing the wedge into the mould.
The shape of the wedge is very important. When
thrown, it should enter the mould and strike the
bottom of the mould first without touching the
sides. To do this, the length and the width of the
throwing wedge should be slightly less than the
length and width of the mould.
When the wedge is made and thrown correctly,
the soil will spread out along the bottom of the
mould first before filling the sides of the mould.
The releasing agent prevents the clay from sticking
to any part of the mould and as a result allows the
green brick to slide easily out of the mould.
When the wedge is poorly made or thrown, the brick
will not slide out of the mould easily. This happens
because the mould has cut off the releasing agent
from the side of the wedge causing the exposed soil
to stick to the mould.
Forming and throwing the wedge is a skill.
Experience has shown that it may take 100 practice
throws before a new brick moulder is able to make
and throw a wedge correctly. If the brick does stick
to the mould or the finishing of the green brick is
not sharp the mould should be cleaned properly
with cleaning tools – especially the depressions
before attempting to throw a new wedge.
Releasing Agent
The releasing agent is a fine, non plastic, dry
material which coats the throwing wedge. It
prevents the soft soil from sticking to the sides of
the mould and helps the green brick to slide easily
out of the mould. Additionally releasing agent gives
a good colour to the fired brick.
The most important property of a releasing agent
is its fineness and burning colour. The finer the
material, better the finish of the green brick. Also
consumption of material is lesser if finer material
is used.
To test the firing colour of the releasing agent,
take a small quantity in a flat clay crucible. Make
a three stone fire and heat the releasing agent till
it is red hot. The firing material is usually wood.
After cooling observe the fired colour. It gives a fair
indication of the fired colour it will impart to the
green brick.
Normally the releasing agent is fine sand. However
where fine sand is not available, sawdust, coal dust
and even fly ash may be used. Never use coarse
sand as a releasing agent. It will not only decrease
the finishing of the green brick but also increase
the consumption. Normally the releasing agent is
spread as a thin layer over the ground and the soil
ball is rolled over it.
The Mould
This is the device that gives the brick its shape.
There are two major parts to it:
The Mould Box
It is the rectangular container where the brick is
formed. The mould is usually made of good quality
seasoned wood. In some places metal moulds made
of MS sheets, aluminium are also found. In some
parts of western India moulders are habituated to
use moulded plastic moulds.
GREEN BRICK MAKING MANUAL
35
VERTICAL SHAFT BRICK KILN
Usually, the mould is reinforced at the corners
on the outer side by metal angles to give it more
strength. The inside of the mould is lined by thin
metal sheets to help give the green brick a smooth
finish. It also helps in minimizing the wear and
tear and easy sliding of the brick. Consumption
of releasing agent is also reduced by metal
sheet lining.
The Frog
The frog in all types of moulds is made from wood.
It is used to form a cavity or indentation on one
side of the brick. The deeper the frog, lesser will
be the brick weight and simultaneous savings of
soil. It also allows the brick to dry faster and gives
the brick a form which improves its adherence
to cement mortar during construction. Presence
of a frog also acts as advertisement for the brick
manufacturer and enables him to distinguish his
product from others.
Fired brick size 230mm x 110mm x 70mm
Equivalent to commonly expressed
9inch x 4inch x 3inch size
Shrinkage
Rate
Interior Mould Dimensions
Length
Width
Height
4%
239mm
114mm
73mm
5%
242mm
116mm
74mm
6%
244mm
117mm
74mm
7%
246mm
118mm
75mm
8%
248mm
119mm
76mm
9%
251mm
120mm
76mm
10%
253mm
121mm
77mm
Making a Wooden Mould
Before making a wooden mould for brick making
two things must be determined: first, the final size
Table 4: Interior Mould Sizes
Fired brick size 255mm x 122mm x 78mm
Equivalent to commonly expressed
8inch x 4inch x 4inch size
10inch x 5inch x 3inch size
36
Shrinkage
Rate
Interior Mould Dimensions
Length
Width
Height
81mm
4%
208mm
99mm
99mm
128mm
82mm
5%
210mm
100mm
100mm
270mm
129mm
83mm
6%
212mm
101mm
101mm
7%
273mm
131mm
83mm
7%
214mm
102mm
102mm
8%
275mm
132mm
84mm
8%
216mm
103mm
103mm
9%
278mm
133mm
85mm
9%
218mm
104mm
104mm
10%
281mm
134mm
86mm
10%
220mm
105mm
105mm
Shrinkage
Rate
Interior Mould Dimensions
Length
Width
Height
4%
265mm
127mm
5%
268mm
6%
GREEN BRICK MAKING MANUAL
of the fired brick and secondly, the overall (both green
and fired) shrinkage of the soil from the moulded
state to the fired stage.
cleaned thoroughly. After each such cleanings the
mould is sprinkled with releasing agent for furthur
fresh mouldings.
Once the fired brick size has been decided, the
interior dimensions of the mould can be calculated.
Remember that most of the red clay bricks have a
shrinkage rate between 4% - 10%. Soils with shrinkage
lesser than 4% will not develop any binding properties
making the brick weak and fragile. Soils with shrinkage
higher than 10% will be difficult to control especially
the fired dimensions. A little bit of more water will
change the dimensions by 1% - 2%. Moreover greater
the shrinkage, higher is the chances of the green brick
developing shrinkage cracks and warping during
drying.
Bow Cutter
For any brick production to get a balance between
reasonable strength and productivity with minimal
green brick rejection a shrinkage rate between 6% 8% is ideal.
The best way to determine the shrinkage rate for
a particular combination of soil and additives is to
entrust an established laboratory to do the testing.
Never try to do it yourself since determination of
shrinkage rates is the most important step towards
a successful brick making enterprise.
The following table (Table 4) shows the interior mould
sizes for various shrinkage rates to produce three
most common types of fired bricks.
Cleaning Tools
If the wedge is not covered properly with releasing
agent, or if it was not thrown correctly into the mould,
the soil will stick to the sides of the mould. It will
then be necessary to clean the stuck soil from the
mould with a cleaning tool after the brick is removed.
Apart from this after repeated mouldings, soft soil
tends to fill the sharp corners of the mould and the
depressions of the frog. This imparts a rough finish
to the green brick.
To take care of this and ensure smooth and sharp
finish to the green brick a cleaning tool is required by
which the stuck soil is cleaned off from the mould. A
simple sharp blade is required to take out soil from
the depressions. A flat blade is required to clean the
soil sticking to the mould sides.
Generally by experience, after approximately 10 – 15
mouldings the mould needs to be cleaned. When it
is not possible to clean the stuck soil by the cleaning
tools, the mould should be dipped in water and
After the wedge of soil is thrown into the mould, the
excess soil over the mould needs to be removed and
the surface smoothened. The bow cutter cuts and
smoothes at the same time as it is moved along the
top of the mould.
The excess soil is removed and placed to one side.
Never mould the next brick with the cut off soil.
Always use fresh dough. At the end of the moulding
or when the pile gets high enough mix the cut off
pieces manually into smooth dough and mould bricks
separately. After the excess soil is removed from the
top of the mould, sprinkle a little releasing agent over
the freshly exposed surface and smoothen with hand.
This prevents the freshly laid green brick to stick to
the demoulding area.
The bow cutter is a simple instrument and can be
made very easily in any workshop. It is made of a 10
– 12 mm MS rod and bend in the form of a small bow
or a rectangular U. The length of the bend area should
be atleast 4 inches more than the mould breadth. Drill
two holes at the two ends of the bow. Tie a fine wire
at the two ends to obtain a bow cutter. Take care that
the wire is not too fine. It will break if it encounters a
solid particle. It should not also be too thick. The finish
of the green brick will suffer. Regularly clean the bow
cutter since during cutting there will be chances of
organic matter sticking to the wire.
Demoulding Yard
After the green bricks are made, they are generally
demoulded on the ground. Before start of moulding
considerable time and effort is spent on preparing
the ground for demoulding.
Before start of moulding the ground upon which bricks
will be laid should be made leveled. All vegetation and
traces of roots should be taken off. One day earlier
before moulding the ground is sprinkled with water.
Take care not to put too much water. Enough water
should be sprinkled so that the surface gets moist.
After about 6-8 hours with a curved round base tool
the ground is furthur leveled. The tool is made from
cutting out the base of a curved metal container
(termed tasla or kadai in India). Locally this is termed
as ring.
Before moulding, releasing agent is sprinkled over the
ground so that freshly laid bricks do not stick to the
ground.
GREEN BRICK MAKING MANUAL
37
VERTICAL SHAFT BRICK KILN
After every 4-5 demouldings the ground is again
leveled with the help of a ring. To keep the ground
leveled, ensure that no heavy vehicle movement
is allowed over it. Always stack the bricks on the
periphery of the moulding yard so that tractors or
hand carts can transport bricks.
After coming out of the mould the bricks lie flat on
the ground. At this time they cannot be handled
since they are very soft. If the ground is not leveled
the green bricks assume the level of the ground and
will warp due to undulations.
In some cases, to get a better finish and shape
concrete platforms are also constructed for
demoulding bricks. This is the most suitable way for
ensuring good quality. However it is costly and small
scale brick makers often will not be able to afford it.
Soft Mud Extrusion
Soft mud moulding process is similar to sand mould
moulding process but done through mechanized
means. It does not require skilled workers and can
be operated with women also. The water content in
the bricks is similar to hand moulding at around 1520% but much higher than stiff extrusion moulding
which is a round 5-8%. These bricks are dried in
open atmosphere.
The quality of soft mud moulding bricks are much
superior to normal sand or slop moulding as usually
followed in Malawi. During the pugging action
followed, the soil, water and other additives get very
uniformly mixed with a de-airing action. This mixes
the material uniformly and increases the density
of the pugged soil. Thus bricks made by soft mud
moulding process has a 20-30% more density than
normal slop or sand moulding.
The equipments required for soft mud moulding
as under:
Machine
In a soft mud moulding machine the main parts
are motor driven by electricity or diesel engine.
The power consumption of the motor is 7.5 HP. This
machine is also equipped with a water recirculation
pump whose capacity is 16 litres/second.
Stainless Steel Mould
The other component of the machine is stainless
steel mould. Three bricks can be made out of one
stainless steel mould. The minimum no of mould
provided in a machine is 24 or it depends up on the
capacity of a machine.
38
GREEN BRICK MAKING MANUAL
Figure 22: Soft Mud Moulding Machine
5.5 The Moulding Process
Soft Mud Extrusion Moulding
In soft mud moulding process soil have to be
dumped in a longitudinal way so that the machine
can be moved along with the dumped soil. The
design of soil stacking down the moulding yard
is very important. The total length in width-wise
between dumped soil, machine and de-moulding
area should not exceed 70 ft to get optimum output
of bricks in numbers to the rated capacity of the
machine (Refer Figure 23)
The following are the stage of moulding in a soft
mud moulding machine.
Stage 1: Dumping of Soil
Dumping of soil in the moulding yard is one of
the most important jobs in the moulding process.
Soil should be dumped in a longitudinal manner.
While doing so care must be taken that the height
of dumped soil should not exceed 2ft and width of
the dumped soil should not increase 10ft.
Stage 2: Ageing of soil
Process of ageing of soil is same as for hands
moulded bricks moulding process.
Stage 3: Feeding of Aged Soil
After ageing the prepared soil is fed to the
machine manually or mechanically (with the help
of conveyor belt). In manual process there are 3 to
4 labour required to feed aged soil in the machine
continuously. In mechanical process 2 labours
continuously shovel aged soil in the conveyor belt.
Stage 4: Pugging of Aged Soil
Step 2: Storing Pugged Soil at Moulding Yard
This activity is done by the machine. The horizontal
Augur is mounted in the machine which is mounted
on bearing at the either end of the machine. This
Augur is having portable blades attached in it which
act as horizontal pugmill. This Augur not only pugs
the aged soil but also helps to fill up the empty
mould with its rotational action.
Storing pugged soil at moulding yard The pugged
soil is stored individual moulders working yard in
such a way that it provides an additional 12 hours
ageing time. The soil is a longitudinal manner
roughly 80 cm width and 40-50 cm height and
covered with a plastic. Once moulding work is
starting themoulder is uncovering the plastic as less
as possible to enable access to the soil for preparing
the dough.
Stage 5: Filling of Empty Mould
The stainless steel moulds are pushed mechanically
to the bottom of the cavity of the barrel designed for
the mould. The moulds get filled up by gravitational
force of the pugged soil and by the action of the
Augur. The filled up mould then pushed up and
taken out by another action of pushing arm which is
connected on the augur. This is continuous process
and one by one the moulds get filled and taken out.
Stage 6: Scraping of Excess Pugged Soil
Excess filled soil in the stainless steel mould is
mechanically scraped off by the action of scraper.
Stage 7: De-moulding of Bricks
Filled up moulds are then de-moulded manually in
the moulding yard. Care must be while releasing the
mould. The mould is moved upside down and with
both hand pressure and it is pushed back. While
pushing back mould should come up vertically
straight.
For more details, please refer to the User Manual
on TARA BrickMek-SUPER, the soft mud moulding
technology.
Sand Moulding
The details of sand moulding are similar to all
countries. The only difference is the size and
dimensions of moulds. Although a single brick
mould is used in almost all countries in certain
countries moulders do use a 2, 3 or even 4 brick
moulds.
Step 1: Transportation of Prepared Soil
Transportation of prepared soil The pugged soil is
transported to the moulding yard for green brick
making generally by wheel barrow. The soil is
transported and unloaded at the different spots of
the moulding yard as per convenience of moulders.
Step 3: Dough Preparation
Dough is a lump of prepared soil which is rolled over
the releasing agent to decrease the adhesiveness
between the dough and the mould box. The
dough preparation requires skill in order to cut the
correct amount of soil from the stored pile. Too
much cutting of soil implies unnecessary waste of
energy as well wastage of processed soil. Too less
soil implies adding soil in the mould with the risk of
creating a texture.
Step 4: Forming of Wedge
The wedge is a triangular shape of soil having length
slightly shorter than the mould length. When the
wedge has been coated evenly with the releasing
agent, it is thrown into the mould with force.
Step 5: Throwing of Wedge into the Mould Box
After the preparation of wedge it is thrown into the
mould box. To generate a natural force it is usually
thrown from approximately a height of 30-40 cm
above the mould. The art of good moulding is to get
the correct angle and force of throwing the wedge
into the mould. The shape of the wedge is very
important. When thrown, it should enter the mould
and strike the bottom of the mould first without
touching the sides. To do this, the length and the
width of the throwing wedge should be slightly less
than the length and width of the mould. When the
wedge is made and thrown correctly, the soil will
spread out along the bottom of the mould first
before filling the sides of the mould. The releasing
agent prevents the clay from sticking to any part of
the mould and as a result allows the green brick to
slide easily out of the mould.
When the wedge is poorly made or thrown, the brick
will not slide out of the mould easily. This happens
because the mould has cut off the releasing agent
from the side of the wedge causing the exposed
soil to stick to the mould. Forming and throwing the
GREEN BRICK MAKING MANUAL
39
VERTICAL SHAFT BRICK KILN
wedge is a skill. Experience has shown that it may
take 100 practice throws before a new brick moulder
is able to make and throw a wedge correctly. If the
brick does stick to the mould or the finishing of
the green brick is not sharp the mould should be
cleaned properly with cleaning tools – especially
the depressions before attempting to throw a new
wedge.
Step 6: Compaction of Dough
After the wedge is thrown into the mould box
with force, it is compacted with hand. Care should
be taken not to produce excessive pressure at
a particular region. This makes brick irregular
in shape.
Step 7: Cutting of Excessive Dough and Levelling
Once the dough is compacted the excess soil on
the top of the mould must be removed and cut by
bow cutter. Care should be taken that the cutting is
straight and in a horizontal line. Excessive pressure
should not be put during the cutting since this will
cut the dough in an irregular and concave manner
thereby reducing the thickness of the brick.
40
GREEN BRICK MAKING MANUAL
Step 8: Releasing and Levelling
After the soil is properly compacted in the mould,
the green brick is demoulded in the moulding
yard. The green brick is released from the mould
with great care. It should be pulled gently and
in a perpendicular direction of the brick. The
consequence of rough or irregular pulling destroys
and bends the corner of the green brick. After the
brick is demoulded into the ground, it is pressed
gently by the bottom of the mould. This ensures
that all corners are straightened and the edges are
sharp.
Step 9: Cleaning of Mould
Moulds should be cleaned after forming of roughly
10 to 15 bricks. If the mould is not cleaned regularly
the finish of the green bricks decreases. Once
moulding work is completed the wooden box must
be dipped into water and left overnight until the next
moulding. This ensures that no cracks will develop,
keep the box in correct shape and increases its life
span.
Chapter 6
Drying, Stacking
and Storage
Process
6.1 Introduction
First Drying Phase
Brick production consists of four main processes:
raw material preparation, moulding, drying and
firing. Each process has an influence on the fired
brick production and quality. Although drying
does not assume importance in favour of the
other processes, still it is one of the most critical
processes for getting an appropriate fired brick
quality.
In this phase the energy, mostly as heat from
sun rays is transferred from the surrounding
environment to evaporate the surface moisture
from the green brick.
The primary objective of this chapter is to
understand the drying process and the factors
which control its properties. This would help in
finding a balance between the property required
in the fired brick and the time of drying that can
be allowed. Drying assumes more importance in
a VSBK firing system, since it is a short cycle firing
and more drier the bricks better the results. Dry
bricks save on energy since the fuel used is utilized
for chemical reactions and not for removal of
moisture. Proper drying of green bricks in VSBK
firing system assumes importance since even with
3% free moisture present in the green brick about
14.8% of total heat input is wasted in driving off
this moisture.
Second Drying Phase
Upon completion of first phase, the internal
moisture within the green bricks is transferred to
the surface and is subsequently evaporated.
The rate at which drying is accomplished is
governed by the rate at which the two processes
proceed. Energy transfer as heat from the
surrounding environment to the wet solid can occur
as a result of convection, conduction or radiation.
In some cases drying occurs as a combination of all
three effects. In most cases heat is transferred to
the surface of the wet solid and then to the interior.
Water exists in a green brick in three different
forms:

6.2 Drying Principles
Drying in brick making commonly refers to the
process of thermally removing moisture to yield a
solid product. Thermally removing the moisture can
be attained by either mechanical heating (dryer)
or atmospheric drying (exposure to sun rays). In
common brick making, and in future discussions we
will be limiting only to atmospheric drying.
How Does Drying Occur?
When a wet solid is subjected to thermal drying,
two processes occur simultaneously:

Moisture

Free water

Water of saturation
Hygroscopic water

Chemically combined water
The process of drying deals with the removal
of various forms of moisture present within
the green brick. A part of the moisture exists as
free water, which fills the pore spaces within the
soil mass and imparts plasticity to it. Once this
moisture is removed, the soil is rigid and does not
flow under moderate pressures, but still looks wet
in appearance. This condition of a green brick is
GREEN BRICK MAKING MANUAL
41
VERTICAL SHAFT BRICK KILN
termed as “leather hard”. Removal of free water is
the first phase of drying. It occurs relatively faster
and is completed within the first 24 – 48 hours after
moulding. The remaining part of the moisture, water
of saturation, is the water clinging to the surfaces
of grains after the pores have been dried up from
their free water.
The free water and the water of saturation can be
removed by evaporation. Hygroscopic water (also
called equilibrium moisture content) exists because
of vapour present in the surrounding atmosphere
which is a manifestation of the relative humidity
of the atmosphere. It generally does not have any
connection with the amount of water added within
the soil during moulding. This water cannot be
removed by atmospheric conditions. It can only be
removed by heating to 120OC.
For removal of chemically combined water within
the structure of phases, heating to 200OC – 800OC
is essential.
Internal Factors
Moisture Content within the Brick
During manual moulding of green bricks the
minimum moisture content varies between 25% 35%. The moisture content is a factor of the ease
of workability of the soil and moulder habits. High
moisture content within the green bricks will take
longer time to dry compared to those moulded with
lesser water.
Soil Characteristics
External Factors
Soil plasticity and the grain size is an important
characteristic to determine the drying times. Finer
the grain size higher will be the plasticity resulting
in more closed packing of the grains. This will result
in lower amount of open pores or finer size of them.
More sandy the soil higher will be the amount of
pores and their chances of interconnectivity. Bricks
with larger concentration of pores i.e. sandy soils
will dry faster compared to bricks made with clayey
soil due to enhanced capillary action.
Atmospheric Temperature
Brick Moulding Type
Increased atmospheric temperature (e.g. summer
months) provides higher energy input. Hence
higher drying rates are expected. Thus during the
day time in summer months highest rates of drying
are experienced. Depending upon the climatic
conditions sometimes the rates are so high that
outdoor drying of freshly moulded bricks results in
dry shrinkage cracks within a few minutes.
Brick moulding patterns also has a role to play in
determining the drying rate. More compact the
brick, lesser will the amount of pores and the water
content. Thus it will dry faster. Thus hollow soil
blocks dry much faster due to greater surface area
exposed to atmosphere and higher area of surface
diffusivity.
6.3 Factors Affecting Brick Drying
The following factors affect the drying rate of a brick.
In most of the cases two or more factors contribute
to the effect.
Relative Humidity
Relative humidity in the atmosphere gives a
measure of the moisture content in the atmosphere.
Higher the moisture content lesser will be the
capillary action for evaporation of water from the
pores of the brick. Lower relative humidity means
lower vapour pressure in the air thus increasing the
drying rates.
42
established around the green brick. These situations
retard the drying process. It is therefore necessary
to have enough movement of air across the drying
surface and around the drying brick to drive off this
moisture. Increase in the air velocity thus enhances
the drying rates.
6.4 Behaviour of a Brick
during Drying
Air Velocity
There is a marked difference between the drying
rate during the night (or more precisely when there
is no sunlight) and day (when there is sunshine).
The drying rate is very fast during the day and slow
during the night. Even during the initial period
there is no drying at the night. At the latter part of
the drying even condensation takes place during
the night.
During drying of a green brick, due to excess
removal of moisture and its higher density than the
air, there is a tendency for a moisture gradient to be
Depending upon the temperature and the relative
humidity content, the initial 1-2 days of drying is
extremely important. If the drying takes place too
GREEN BRICK MAKING MANUAL
fast, then there is a chance of the bricks to develop
cracks due to differential shrinkage between the
surface and the central part. During this stage the
bricks tend to warp also. Since the bricks are laid flat
on the surface, the exposed portion dries out much
faster than the surface in contact with the ground.
Drying accompanies shrinkage. Thus the brick tends
to bend in a concave manner.
In the latter stage after 1-2 days the bricks should
be placed on the smallest surface to enable drying
from all directions. Otherwise there might be small
cracks formed inside the brick which cannot be seen
with the naked eye. These cracks eventually expand
during the firing process resulting cracks during
firing or loss of strength.
6.5 Determination of Drying
The following simple drying tests are, if carried
out regularly, not only help to master the drying
process but also enable to judge the final quality
of the product.
Weighing Test
Procedure: Weigh 10 green (just moulded) bricks.
List down their weights, dimensions and the time of
moulding and each measurement. Each day weigh
the green bricks and record the weights.
Inference: The difference between weight and dry
bricks can be used to determine the rate of drying.
When the dry green weights of the bricks become
constant and do not change for 2-3 days of
measurements, the green bricks are optimally dried.
Inference: If there are no visible colour difference
than the bricks are absolutely dry. However there is
a distinct colour gradation between the periphery
and the central core than the bricks have not dried
properly.
Sound Test
Procedure: Take two dried green bricks from the
stack. Hold the two bricks with two hands. Strike
them lightly.
Inference: If there is a dull sound then the bricks
have not dried properly. However, if the bricks make
a sound when two wooden pieces are struck then
the bricks are sufficiently dried.
6.6 Stacking Patterns and Its
Effect on Drying
After drying to leather hard conditions on the
moulding yard, green bricks are ready to be lifted
and stacked in rows. This is usually done to

Allow full airflow circulation for further drying

Create space in the moulding ground for further
moulding
Leather hard condition is determined physically by
the condition when there will be no finger prints on
the green bricks during handling. Also at this stage
the green brick can be handled with four fingers of
a hand.
Water Vapour Test
Procedure: Select any brick considered to be dry.
Take a transparent airtight plastic bag, put the green
inside it and seal the opening. Keep the sealed
plastic bag with green brick in the open sun for
about 2 -3 hours.
Inference: The brick will start to heat up. Any resident
water inside the brick will start to evaporate. If
moisture appears on the inside of the sealed plastic
bag, then the bricks are not properly dried yet.
Breaking Test
Procedure: Select any green brick considered to
be dry. Break it into two halves. Look at the central
surface of the broken pieces.
Figure 24: Different Patterns of Stacking
GREEN BRICK MAKING MANUAL
43
VERTICAL SHAFT BRICK KILN
Stacking of green bricks requires special attention
and only well trained workers can do it in a wellmanaged way. Generally the stacking is done by
moulders itself. Stacking is usually the process of
keeping the green bricks in rows. Generally a stack
of 10 layers are used for drying. The height is usually
followed due to convenience of stacking. Various
patterns of stacking are followed in brick making.
In some parts a herringbone pattern of stacking
is followed. However the most generally followed
pattern is by keeping the bricks crossed. This allows
for faster and even drying.
If the stacking is not uniform and proper air gap is
not provided then there will be uneven drying of
bricks. The surfaces in contact with each other will
always remain moist. This will result to cracking of
the green bricks.
Whatever the stacking pattern, always there has to
be a gap of atleast 3 – 4 cm between each and every
brick for proper airflow. (Refer Figure 24)
6.7 Process of Natural Brick
Drying
Moulding Yard Drying
After the green bricks are moulded allow 1-2 days
for drying to leather hard conditions. This is defined
by the ability to handle a green brick with four
fingers without damage or distortion. Remember
that the time stated here is hypothetical and will
vary depending upon your local conditions.
After placing each brick ensure that the right gap
is maintained.
If there are any bricks found deshaped or cracked
reject them and send them to the recycling yard.
Always keep a plastic sheet ready for covering the
stack from unseasonal rains.
6.8 Various Stacking Platterns
and Storage of Green Bricks
Storing of green bricks is usually stored for firing in
the rainy season. During the summer months green
bricks dry faster. Thus the rate of production will be
very high. These bricks after proper drying needs
to stored for future firing. There are two things to
be kept in mind during storing. Firstly the storing
pattern should be such that damage due to rain will
not occur. Secondly it should be economical and not
cover much space.
Generally for making the storing chamber calculate
the number of bricks one needs to store. It is
advisable to make more number of small stores
than a single very large store. This is done to ensure
less damaged bricks. Depending upon the dry green
brick strength the stack height varies between 20 to
30 brick height.
Once the area is calculated, and the site selected
for storing clear the area from any vegetation. After
cleaning the land should be levelled properly. Place
at least three layers of fired bricks to make the base.
After 1 – 2 days turn the bricks on their length.
This will ensure more surface area exposed to the
atmosphere and even drying. This type of turning
on edges also helps in reducing warpage.
After again 1 – 2 days turn the bricks on their
width. This is the position of the bricks where the
maximum surface area is exposed.
Stack Drying
When the bricks are properly dried from the surface
they are now ready to place in the drying stack. This
situation is judged by pressing your finger on the
bricks. If the green bricks still feel soft or else there
are finger marks keep it in the moulding yard for
further drying. If the bricks feel hard and there are
no finger marks they are ready for stacking.
During stacking carry two bricks at a time with
your two hand and place it gently on the stack.
44
GREEN BRICK MAKING MANUAL
Figure 25: Storage of Green Bricks
The level might be varied so that during rain water
does not flow over the green bricks.
Start placing the green bricks from one corner.
Ensure that there should be no gap between the
bricks. Always start stacking of bricks from one side
only. If haphazard stacking is started then there will
be chances of gaps when the stack meets together.
Initially the stack should be vertical. The height of this
type of stacking might vary. Generally it is half the
length of the total stack. After reaching the desired
height the stacking of the green bricks should be
made in such a way that a sloping roof is made.
(Refer Figure 25)
After completion of the stack cover the top with
a thick plastic. Please remember that the plastic
should cover only the top to protect the bricks from
rain damage. On top of the plastic place red bricks
all along. Alternatively you can put a layer of burnt
coal ash and then a layer of red bricks. This is done
to prevent the red bricks against slipping during
heavy rains.
When using the store, keep a plastic. During
transportation intervals keep the whole stack
covered with plastic so that sudden rains do not
damage it.
GREEN BRICK MAKING MANUAL
45
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