TECHNICAL PAPER #70
David W. Thomas
V. F. Nast
1600 Wilson Boulevard, Suite 500
Arlington, Virgnia 22209 USA
Tel: 703/276-1800 * Fax:
Understanding Small-Scale Brick Making
1990, Volunteers in Technical Assistance
This paper is one of a series published by Volunteers in
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the lime and cement business, and Victor Palmeri, a
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UNDERSTANDING SMALL-SCALE BRICK MAKING
VITA Volunteer David W. Thomas
THE INVENTION OF FIRED BRICK
Sun-dried earthen blocks (adobe) have been used as a
material for thousands of years, especially in very dry
Clay is mixed with water, and sometimes straw to keep the
blocks from cracking, and formed by hand into blocks.
blocks are placed in the sun until they are thoroughly
dried blocks are hard, but they soften and come apart in
The invention of more durable "fired" or baked
brick was an event
of enormous importance.
Nearly 7,000 years ago people discovered
that exposing clay to high heat would convert it to a hard,
glassy material (called ceramic, from the Greek word for
pottery). The first
ceramic materials were cooking vessels
and figurines; eventually, about 3,500 years ago, the technology
was applied to building blocks.
Like sun-dried blocks, fired bricks were modular and easily
But fired bricks were very hard, as well as resistant to
attack by weather and fire.
They were usually cheaper than stone
and often could be manufactured close to building
technology made it much easier for people to make durable
buildings, walls, roads, and bridges.
The Romans combined brick
with concrete and developed new kinds of buildings.
New kinds of
cities, political institutions, and arts flourished.
and refined ceramic technology produces not only building
materials, but special porcelains, glasses, and even such
devices as radio transistors and computer chips.
bricks are flat and rectangular, their relatively small size
irregular surfaces require the use of mortar for assembly
walls and other structures.
Mortar is an adhesive made of cement,
lime, and sand, to which water is added at the time of use
make a paste. It hardens
in a few hours.
Today, 65 percent of the bricks made in the world are used
dwellings; 35 percent are used for walls, public buildings,
other non-dwelling structures.
In addition to common or ordinary
building bricks, there are glazed and other decorative
special "firebrick," designed to protect surfaces
heat. Bricks can be
manufactured by large automated factories;
they can also be made on a small scale by one or two
working together in a rural setting.
This paper describes the
small-scale manufacture of ordinary bricks.
Building bricks are made with clay and water, and fired with
locally available fuels.
Strenuous physical work is involved.
rewards, on the other hand, are enormous.
Durable housing that
resists the elements generates a feeling of purposefulness
security to those so sheltered.
The comfort and improved health
that comes with living in a dry house, one that holds warmth
cool weather or remains cool in the hot sun, reward the hard
THE TECHNOLOGY OF FIRED BRICK
Clay is often abundant in old river and lake beds because it
the finely granular end product of the breakdown by water of
rocks and minerals.
The minerals from which clay is derived contain
oxides of such common chemical elements as aluminum, iron,
manganese, and silicon, as well as other compounds of
and silicon. When
exposed to high heat (900 [degrees] C or more), some of
the materials melt to form a glue that holds the unmelted
process is called vitrification; the melt
becomes glassy when it cools.
Brick must be strong; strength
comes from vitrification, the kinds of chemicals in the
the temperature and duration of firing.
The color of fired brick
is usually rust-red because of the abundance of iron oxide,
In primitive manufacture, clay may be dug and bricks formed
hand to produce 20-30 bricks per day.
Developing the desired.
hardness through crude firing may result in bricks of low
and is usually accompanied by inefficient gathering of
rural brick making can be more efficient.
Its five processes,
described below, are as follows:
1) winning or mining the clay;
2) mixing the clay with water to "plasticize" it or
make it moldable
by hand; 3) forming or shaping the bricks; 4) drying them;
and 5) firing them in a special furnace, the kiln, to
PREPARING MOLDED BRICKS FOR THE KILN
Clay winning and clay preparation are often combined.
worker chips away small amounts of a clay bank with a hoe or
adze. If the clay
formation is shaped like a flat lens at the
ground surface, the worker digs a hole about one meter deep
three meters in diameter.
Then, with short chopping strokes, the
worker "shaves" the clay from the wall of the
hole. The flakes of
clay so removed are less than a centimeter thick.
They may curl
as they are removed from the clay bank face.
Where the clay appears
as an outcropping on the side of the hill, the operator
moves the flakes to a small pit or hole nearby.
The hole receives
the shavings and provides a location where the clay, newly
from the bank, can be mixed with water.
The shavings are quite
light compared to the clay remaining in the bank face.
Now, small amounts of water are worked into the clay,
treading with the feet.
People characteristically dance and hop
when they mix water and clay in this manner.
Often, one person
chips the clay face while another mixes the clay with
the mixture reaches the paste-like consistency that is
(as judged from experience), it is placed in a bucket or, if
available, a wheelbarrow, and removed to the brick-forming
Forming the Bricks
There is no "standard" brick size, but setting the
length of the
fired brick to a little more than twice its width allows a
of bonding patterns during bricklaying.
The dimensions of
fired bricks usually depend on local tradition, but are
to 22 cm long, 9 to 11 cm wide, and 5 to 7.5 cm thick.
the unfired bricks are made larger than the finished size,
allow for shrinkage during firing.
The amount of shrinkage depends
upon the clay and the firing conditions and is learned by
Bricks are formed simply by pouring or dumping the
mixture into a mold that has up to four cavities, so that
bricks are formed at one time.
The mold is usually made of wood
and is open on both faces (Fig. 1).
It has handles at each end
for handling and lifting.
The molds are coated with oil or sand to make it easier to
the formed bricks from the wooden sides.
If sand is used, grains
about 0.5 mm in size are sprinkled on the mold surfaces
mold has been immersed in water.
Oil is scarce in most places,
but where it can be used it will be absorbed by the brick
burned during firing, thus providing part of the fuel
The molds are filled on level ground.
Usually, two operators are
needed in the casting or pouring of the bricks.
After the bucket
of clay-water mix has been poured into the open mold cavity,
mold is vibrated slightly by striking it with the heel of
hand. This causes
the material to settle and level off at the
top. Some water is
absorbed by the ground; some comes to the top
and runs off. Excess
material lying on top of the mold is then
pushed off with the hand or a board and saved for the next
The consistency of the mixture is critical.
Mixtures that are too
watery tend to flow or cause the bricks to slump when the
lifted free of the mixture.
Mixtures that are too stiff may not
fill the corners of the mold.
The bricks will then be irregular
and jagged. Once the
proper consistency, or water-clay ratio, is
determined by experiment, the pit operator ensures that it
maintained throughout the working day.
After excess clay is removed, the mold is lifted up and
the cast brick. Two
persons are needed to lift the mold vertically.
Once free of the bricks, the mold is again wetted with water
and sand is sprinkled on the inner surfaces.
It is then placed on
the ground in front of the bricks just released from the
Thus, the brick making process becomes continuous, the mold
progressively to make row after row of bricks.
Drying the Bricks
The drying ground
should be level and free of surface irregularities.
An open and shade-free area is preferred to speed drying.
If daily rainfall is expected, the formed bricks are protected
with a cover that has no sides, so that the air can move
around them. After
about three days in the flat or "as made"
position, the bricks can be handled without deforming or
them. At this stage,
they must be stacked in a special
manner to speed up the final stages of drying.
Figure 3 shows an effective stacking pattern for drying
Two bricks are first placed on the ground resting on the
that is approximately 20 cm by 6 cm and one brick-length
Then two bricks are placed upon the first two, at right
them, so that the second two bricks cover the ends of the
pair. To achieve
stability as the pile grows taller, a "tie
brick" is used, extending from the center of one brick
center of another that is at the same level in an adjacent
Thus, the tie bricks link each vertical column of bricks to
growth and alternate tie-brick placement continues
until the drying stack is about 1.5 m high and of any
convenient length, generally about 3 m.
The bricks are dried by prevailing winds that circulate
the open spaces of the stack.
The additional factors that favor
rapid drying are: 1)
high air temperature; 2) low humidity; and
3) using clay containing a small proportion of very fine
which hold more water.
A clay that has a large proportion of extremely fine
will absorb and hold more water, the evaporation of which
cause bricks to crack.
This fault can be corrected by adding some
sandy material to the clay mix.
The sand should be fine, with
most of the grains smaller than 0.5 mm and a few as large as
At least a week is needed for complete drying.
The stack must be
protected from rain during this time, because the bricks
lose strength or even crumble if they get wet.
Both the top of
the brick stack and the base must be protected.
that will shed ordinary rainfall is provided by placing a
pieces of lightweight corrugated metal upon the bricks (Fig.
Bottom protection is provided by building the stack upon a
course of previously fired bricks.
Fired brick is resistant to
water and will remain hard when wetted by runoff.
Drying is a critical process that requires the exercise of
Bricks with even a trace of water should never be placed
in the kiln. If the
water content is too high, a brick may explode
in the kiln when heated.
Completeness of drying can be
tested easily because clay usually assumes a lighter color
dries. Upon being broken
in half, a thoroughly dried brick shows
no color difference between the outer part and the
method is to weigh a brick taken from the stack.
it near an oven or other heat source for a few hours.
If it loses
weight, the bricks in the stack f rom which it was taken are
to be incompletely dried.
BUILDING THE KILN
Where bricks are made on a very large scale, firing is a
process for which a tunnel kiln is used.
Such a kiln is the
largest single investment for the manufacturer and can cost
half million dollars or more.
In making bricks on a small scale, firing is a batch
Kilns can be built of locally available material and can be
with local fuels.
The bricks are placed in the kiln, the fire
started and needed temperature is reached.
After several days of
firing, the fuel supply is stopped and the kiln and its load
allowed to cool down naturally.
The kiln consists of the fire box, the flue system, the
side walls, and the mudded end walls.
Haste in building the kiln
can result in shoddy side walls and fire boxes, which, in
results in constant and time-consuming repairs.
The Fire Box
The fire box is an opening in the permanent side wall into
the operator places the fuel.
It usually measures 60 cm wide, 100
cm high, and 75 cm deep.
The top can, but need not be, arched.
the center of the 60-cm span, about 50 cm from the ground,
rods or grid bars are placed horizontally.
The bars are 2 cm in
diameter and are placed 7.5 cm apart to support the
are secured by embedding them in the bricks on both sides of
opening (Fig. 5).
The Flue System
The flue system includes the openings that let air and hot
enter and leave the kiln, as well as spaces among the bricks
stacked in the kiln for firing.
It allows free movement of hot
gases from the heat source in the fire box, to the bricks
fired, and finally to the upper parts of the kiln and out
provided openings, just as smoke and heat travel up a
bring this about, the bricks must be stacked as described
under "Loading the kiln."
The Permanent Side Walls
The two identical, permanent side walls are built of
fired brick; the fire boxes are apertures located in
walls are usually placed about 3 m apart and perfectly
The bricks to be fired are placed in the area between the
The walls are normally two brick lengths or 50 cm thick
It is not necessary to have a supply of fired bricks on hand
build a first kiln.
The side walls and fire boxes can be made of
unfired brick; such a kiln is much smaller than the one to
After the first firing, perhaps as many as 50
percent of the bricks in the kiln will develop enough
be used. These are
set aside; continued firings will yield an
accumulation of bricks to make two full-sized side walls.
The Mudded End Walls
The mudded end walls are two temporary closures at the ends
the permanent side walls, constructed after the kiln is
They are taken down to remove the load of bricks after
The mudded end walls may be made of previously fired or
bricks placed directly on each other (Figs. 6 and 7).
between the bricks are filled from the outside with a
brick clay and water; it is smeared on by hand in the same
spreading plaster on a house wall.
The purpose of the mud is to
prevent the escape of heat from the kiln between the bricks.
Bricks used for these walls are seldom exposed to the heat
would harden them.
For this reason, they are set aside to be
placed in the inner kiln areas during later firings.
LOADING THE KILN
Once the kiln side walls and fire boxes are assembled, the
may be loaded with dried bricks.
Careless haste in placing the
bricks in the kiln can result in collapse of the entire
usually resulting in a complete loss of the batch of bricks.
The dried bricks are first arranged between the permanent
in the areas close to the fire box.
Bricks in the fire box area
are placed one pair on top of another, with pairs at right
to each other, as in the drying stack.
The same tie-brick system
is used to give stability to the columns of bricks.
Once these areas are filled, the inner sections of the kiln
loaded. Here, the
stacks of bricks are placed farther apart to
allow free movement of hot gases.
The keying technique is extended
in two directions.
In order to prevent internal topple or
insecure and unstable piling of bricks, the rows are keyed,
to the other, by placing the second row of bricks close to
1 cm away from) the bricks in the first column.
The bricks are
arranged so that the sides of the bricks in the second row
columns are placed against the ends of the bricks in the
row. This setting is
reversed for the next row, and so on until
the entire kiln is loaded (Fig. 7).
Bricks in the ends of the kiln, close to the mudded end
are placed closer to each other to reduce the escape of heat
through these walls.
When the top course of bricks is built to
form the kiln roof, its bricks form a solid platform
by open areas 60 cm square (Fig. 8).
As in the case of the end
walls, the close-set top bricks are mudded over to prevent
escape of gases and heat through cracks between them.
The flue system or draftway now extends from the fire box,
through the stacks of bricks to the top of the kiln.
It is at
this point that the set of firing controls required on the
is installed. Pieces
of sheet metal are provided that slide over
the various openings to control the amount of hot gases that
escape from the flue space.
Thus, a piece of metal about 90 cm
square is needed for each 60 cm by 60 cm opening in the top
the kiln. To create
a greater draft and make the fires hotter,
remove the covers.
To dampen the fires and to hold the heat as
long as possible, slide them over the openings, thus
the passage of gases and heat from the kiln.
FIRING THE KILN AND ITS CONTENTS
The Heating Period
Using wood as fuel will create the high heat necessary for
firing of the kiln.
It should be cut into 1.75-meter
successful fuels include coffee husks, coconut
hulls, dung, olive pits, and even burnable fabric
scraps. A good
supply of fuel in ready condition should be on hand when
is started. A fuel
shortage in the middle of a firing can result
in loss of the entire load of bricks.
The fuel is placed on top of the grate bars and (for wood)
only to the inner edge of the permanent side walls; it is
pushed inward as the ends are consumed.
A small fire is now
started under the grate so that the flames traveling upward
ignite the fuel above.
The metal covers on top of the kiln are
opened to permit free access of air and create a draft from
fire box upward.
When the fuel is burning, the space under the grate bars
entry of air for continued combustion.
The space can be blocked
with excess fuel or ashes, thus providing an additional
of draft. At early
firing stages the area under the grate is free
of fuel or ash.
After the fires have burned and smoked f or 10 to 12 hours,
operator may be able to see a slight reddish glow by viewing
inner part of the kiln through the archway of the fire
the entire inner mass of the kiln has developed a cherry-red
glow, this part of the kiln is at the correct firing
(875 [degrees] C to 900 [degrees] C).
To complete the firing and permit the
of each brick to reach the correct temperature, the flue
draft is retarded by sliding the top covers over about half
the flue openings.
At the same time, the areas under the grates
are blocked with fuel or ash.
These adjustments retard heat loss
from the kiln as well as allow all parts of the kiln to
Holding and Cooling
Firing has now entered the holding or "soaking"
achieved, these conditions must be maintained for at least
hours, adding fuel as necessary.
Because of the reduced draft,
less fuel will be needed than for the first firing stages.
At the end of the holding period, the fuel supply is stopped
the top plates are placed to cover the flue openings
Sometimes, operators also completely fill the openings of
fireboxes with ashes from previous fires to further reduce
loss, thus holding the heat in the kiln as long as possible.
After about two days, the bricks can be removed from the
First, the end walls are torn down starting with the upper
The bricks of the end wall that did not receive full heat
can finished in subsequent firings.
The mud used to close up the
gaps between the bricks can be knocked off and does not
Bricks shrink during firing, sometimes as much as 10
Thus, the stacks of bricks in the center of the kiln may be
after firing than before.
After all the newly fired bricks
are removed from the area between the two permanent side
the entire kiln, including the fire boxes, is swept clean of
ashes, bits of clay, and broken bricks.
It is now ready for another
Scale of Production
The scale of production described here will meet the housing
needs of a few villages.
A large, automated facility is needed
for construction of a new city.
Marketing and Product Diversification
Marketing the bricks should not present problems.
Wood as building
material is already very scarce in many areas, as forests
become transformed into crop and grazing land.
of forests brings about major climatic and other
disturbances, and has properly caused concern among farmers
officials. But clay
is abundant in many places, and the kind of
clay found at the surface of the earth is usually
for making building bricks.
Gaining experience in making common bricks may lead to the
of other clay-based products.
These include tiles for roofs,
walkways, and roadways, and glazed or decorative bricks for
and public buildings.
The processes described in this paper
for building bricks are fundamentally the same for other
products. The clay
for other kinds of brick may need to be mined
from deeper locations.
1. Hand Operated
Clay Crusher for Brickmaking.
9, No. 3, Intermediate Technology Publications,
2. Wade, R.J. and
Mason S.A., Stabilized Brick Manufacture and
Workshop, Papua New Guinea-University.
Papua New Guinea
University of Technology, Department
3. Brandt, W.O,,
Manufacture of Burned Brick by Simple Methods.
Technical Assistance, 1966.
4. Kundu, T.K., A
Feasibility Study of a Gas Fired Brick Kiln
Bangladesh. Thesis No. 1219.
Asian Institute of Technology,