Small Scale Manufacture
 
of Burned Building Brick
 
D.W. THOMAS
 
Manager, Technical Service
Industrial Minerals Division
International Minerals & Chemical Corporation
Skokie, Illinois U.S.A.
 
                             published by
 
                             VITA
                 1600 Wilson Boulevard, Suite 500
                   Arlington, Virginia 22209 USA
              Tel:  703/276-1800 * Fax:   703/243-1865
                    Internet:  pr-info@vita.org
 
 
         SMALL-SCALE MANUFACTURE OF BURNED BUILDING BRICK
 
                           Preface
 
    The purpose of this manual is to outline, in as
simple a manner as possible, the details of making and
burning clay brick suitable for domestic building.   The
scope of the manual is confined to "cottage industries";
it does not cover large commercial production such as is
known in the United States.  The author has had personal
contact with such brickmaking plants in both Central
Mexico and Honduras.  It is hoped that by publishing
some of the observations and experiences made at these
two locations, I can help community development leaders
to offer advice and assistance in developing areas where
brickmaking plants are needed.
 
                    INTRODUCTION
 
          The Materials:  Clay and Fuel
 
    The two principal materials needed to carry out even
elementary brickmaking are (1) a source of clay, and
(2) a reliable source of fuel.   We will expand on the
clay requirements first.
 
                          Clay
 
    Clay is a hydrous aluminum silicate formed by the
deterioration of a number of minerals over a long period
of time.  When glue-like organic material is associated
with it, the clay becomes plastic or hand moldable and
pliable.  It is found throughout the world and has been
treated, since time began, with far less respect than
it deserves.  It is from this ordinary clay that man can
make the brick to house him, the tiles to cover his home,
pipe to carry water to his living area, pipe to divert
sewage, clay pots to store and cook his food, and tiles
to pave his walk and driveways.   Certainly, any material
which in itself can provide all these features should
not be slighted.  How, then, does one select the proper
clay and what, actually, IS the proper clay?
 
    There are four characteristics of clay to consider
when we are thinking of using it as an ingredient in
brick or tiles:
 
    1.   It must be easily available and must be able
        to be won from the earth with a minimum of
        physical effort.
 
    2.   It must be plastic.   This means that when the
        clay is mixed with small amounts of water, it
        will become pliable and will respond to the
        human hand by taking different shapes.
 
    3.   It must develop strength upon drying.
 
    4.   It must develop hard and durable "use" strength
        when fired or burned in a kiln.
 
    Clays are found, for the most part, when topsoil is
removed by stream action or as a result of a road cut.
If a pond or water-collection area is above the normal
level for flowing water, this can mean that a clay mass
is present.  Thus, a pond found in the countryside which
is some 200 feet above the level of a nearby stream would
indicate that there is a very fine material underlaying
the pond and thus the normal outflow of rainfall has been
restricted.  Digging near the banks of such an area of
captured water will generally reveal the presence of a
"lens" of fine grained and plastic clay.
 
    If community development leaders have samples of clay
and are wondering if the material will, in fact, make
good brick, these samples can be sent to ceramic laboratories
in your country or in the United States where
simple, but conclusive tests can be made to find out if
the clay is a possible ingredient for brick forming.
One such laboratory willing to make elementary tests of
clay, and to comment on it, is the
 
                  Ceramic Laboratory
                  International Minerals & Chemical Corp.
                  Post Office Box 437
                  Mulberry, Florida
                  U. S. A.
 
Community development leaders wishing to have local clays
evaluated for their possible use in brick can contact
this laboratory directly.  You should get detailed packing
and shipping instructions from the laboratory before
shipping any material.
 
     Starting and Operating a Brickmaking Plant
 
    This manual continues now with the assumption that a
suitable clay has been found and that it is within easy
access of the proposed user.   We will further assume that
firing or heat-treating facilities do not presently
exist and that there are only very limited sources of
steel or metals.  The fuels will be limited to materials
such as wood scraps and other burnable materials as are
locally available.  In brief, we will now explore the
establishment and operation of a building-brick plant
wherein nothing but "on hand" materials and labor will
be utilized.
 
    Clay brick is made in the following steps:
 
    1.   Clay winning and clay preparation.
 
    2.   Brick forming.
 
    3.   Brick drying.
 
    4.   Kiln construction and brick firing.
 
    5.   Finished product quality selection.
 
1.  Clay Winning and Clay Preparation
 
    It is common, in small one and two-family brick
operations, to combine clay winning and clay preparation.
In general practice, the operator desiring to make the
clay plastic will use a simple hoe or adze to chip away
small amounts of the clay bank.   If the material is
available as a flat lens, he will probably dig a hole
about three feet deep under the level of the earth.   The
hole would be about 10 feet in diameter.   Then, with
short chopping strokes with his adze, the operator will
"shave" the clay from the bank face.   The flakes of clay
so removed will be about 1/4" thick.   In all probability,
they will curl up as they are removed from the clay bank
face.  In those cases where the clay appears as an out-cropping
on the side of the hill, the process is very
similar, but the operator would move his "shavings" to
a small pit or hole nearby.  The function of the hole to
receive the shavings is simply to provide a location
wherein the clay, newly cut from the bank, can be mixed
with water.  The clay "shavings" are quite light and are
not as dense as the clay remaining in the bank face.
Small amounts of water are worked into the clay by use
of the human foot.  A dancing and hopping movement is
characteristic of people accustomed to mixing water and
clay in this manner.  It is common to have one man chipping
the clay face and another person doing the water mix
operation.  When the clay-water mixture reaches the
consistency of pourable concrete, it is placed in a
pail or bucket and removed to the brick-forming area.
An ordinary wheelbarrow at this point would be considered
a most welcome labor-saving device.
 
2.  Brick Forming
 
    The actual brick-forming operation is one of merely
pouring or dumping the clay-water mixture into a multiple-cavity
brick die.  This die is generally made of wood and
is open on both faces.  See Illustration No. 1 for

52p05a.gif (600x600)


details of a typical wooden brick mold.   There may be
as many as four cavities in the die so that each casting
will yield four brick.  The brick themselves are roughly
ten inches long, 2 1/2 inches high, and 5 inches wide.
Actual dimensions will vary from country to country,
depending on local taste and previous performance.   The
above brick, 10 x 2 1/2 x 5 inches may be too heavy or
cumbersome for some female workers.   If this is so,
smaller units can be made.  It should be noted at this
point that the final brick will be smaller than the actual
die or mold with which it was originally formed.   This
firing shrinkage will be dealt with in a later portion
of this manual.
 
    The molds are coated with sand to make it easier to
remove the clay from the wooden sides of the mold.   This
can be done by sprinkling sand the size of grains of
salt on the mold surfaces after the mold has been immersed
in water.  Oil, at a premium in most places, will also
act as a parting agent.  In those cases where oil can be
used, it has a dual advantage in that it will be absorbed
by the brick and consumed by the heat of the kiln and
will actually provide part of the fuel requirements.
The molds are filled on level ground.   Usually, two
operators are needed in the casting or pouring of the
brick.  After the bucket of clay-water mix has been poured
into the open mold cavity, the mold is vibrated slightly
by the heel of the 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 is pushed off.
Excess material laying on top of the mold is then struck
from the mold by a deft movement of the heel of the hand.
The excess material captured in this manner is placed
in another mold and will be used in another brick.
 
    The consistency of the brick mix is a very important
and critical point.  Clay-water mixtures which are too
watery will have a tendency to flow or cause the brick to
slump when the restraining mold is lifted free of the
mix.  Clay-water mixtures which are too stiff or lacking
sufficient mobility will not fill the corners of the
brick mold and the resultant product will then be irregular
and jagged.  Once the proper consistency or waterclay
ratio is determined experimentally, the pit operator
should exercise all possible care to see that this consistency
is maintained throughout the working day.
 
    After excess clay is removed, the mold may be lifted
up and free of the brick castings.   In order to get a
straight up draw of the mold, it is necessary to have two
men perform the operation.  Once free of the brick, 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 brick just released from the mold.   Thus,
the brickmaking process becomes a continuous operation
with the mold moving progressively to make row after row
of brick.  See Illustration No. 2.

52p07a.gif (600x600)


 
3.  Brick Drying
 
    In arid countries, it is not generally necessary to
cover the newly made brick.  They are simply left in the
position in which they were made and allowed to dry in
the sun.  In those areas where rainfall is a daily occurrence,
it is best to provide a covering for the newly
formed brick.  The cover should have no sides so that the
air can move freely around the brick.   After about three
days in the flat or "as made" position, the brick can be
handled without deforming or crumbling.   At this stage,
they are placed in a special manner to speed up the final
stages of drying.
 
    Perhaps the most important factor in drying is the
"hack" or manner in which the brick shapes are stacked
in the drying area.  In Illustration No. 3, right hand

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drawing, is shown a typical "hack" for drying brick.
In this operation, two brick are first placed on the
ground on the face or narrow dimension.   They are placed
as far apart as a brick is long.   Then, at 90 [degrees] to the
first two brick, two more brick are placed on the top
of the first two.  The second placed brick will cover
the ends of the first pair.  In order to establish some
degree of stability in such an open setting of brick as
the pile extends higher, it is recommended that a "tie"
brick be used to keep the stacks of brick from toppling.
The tie brick actually keys one vertical column of brick
into the one adjoining it.  The key, or tie, brick is
placed so that it extends from the center of the first
two brick mentioned above to the center of the pair of
brick placed adjacent to it.   The continued placing of
pair on pair, 90 [degrees] reversal as the pile extends upward,
and the alternate tie-brick placement continues until the
drying stack is about five feet high and of any convenient
length, generally about 10 feet.
 
    Drying is accomplished by permitting prevailing winds
to circulate through the open spaces of the "hack".
Three important factors control the rate of drying:
(1) the heat naturally available, (2) the humidity, and
(3) the amount of fine particles in the clay.   Obviously,
ideal conditions would call for a locale wherein the
heat of the day would stay quite high with the sun shining
most of the time.  Secondly, the lower the humidity,
the more rapid the drying of the brick.   The presence of
extreme fines or very powdery clay will require more water
in the clay-water mixture to form.   As the same fines in
the clay are more reluctant to give up the forming water,
the drying time will thus be extended.   A sandy clay is
more apt to dry rapidly, without cracks, than a clay
which is predominantly fines.
 
    The brickmaker may find that the clay he is using
has a preponderance of extremely fine particles which
causes brick cracking.  He can correct this fault by
adding some sandy material to the clay mix.   The particles
of sand should be the size of grains of salt with a few
as large as match heads.
 
    In any event, it is necessary to provide at least
one full week to insure complete drying.   During this
time, the possibility of rainfall must be taken into
account.  If the stack of brick, as described above,
is standing in an unprotected area and is exposed to the
rain, it is entirely possible that the brick will lose
strength upon being wetted and will slake or crumble as
a result of the newly combined water.   Both the top of
the brick stand and the base must be adequately protected.
Top protection designed to shed ordinary rainfall is
accomplished by placing a few cuts of lightweight corrugated
metal on the top of the brick.   This is demonstrated
in Illustration No. 3, left hand drawing.   During a rainfall,
it is possible that run-off water or pools may
develop around the bottom course of brick.   In order to
protect the stack from becoming weakened due to a water
softening of this bottom course, it is recommended that
the drying stack be built upon a first course of previously
burned brick.  These brick are resistant to
water slaking and will remain rigid although wet from
water run-off.
 
    Local conditions, including the humidity, the persistence
of rain, the amount of solar exposure, the motion
of hot air caused by wind, as well as the nature of the
clay itself, will dictate, to a large degree, when the
drying process is completed.   In any event, it is imperative
that the drying process be complete before the
brick are taken to the final process:   the firing or
burning of the brick.
 
    There are two simple tests to determine if the drying
process is, indeed, complete.   As clay dries, it
changes color.  Generally the color becomes lighter
as the water leaves the clay mass.   Thus, a thoroughly
dried brick would show no color differential, upon
being broken in half, from the outer skin area or the
center section inside the brick.   Another means of
determining if all the drying is completed, is to weigh
a brick taken from the drying hack.   Then place it in
an oven or near a source of heat.   Weigh again.  If
the brick heated in the oven shows a loss of weight,
this means that the brick in the drying pile also must
contain water and thus the drying process is not complete.
 
4.  Kiln Construction and Brick Firing
 
    It is in the firing of the brick that it receives its
strength.  In the presence of high heat, the alkalies in
the clay, together with small amounts of oxides of iron
and other metals are joined, to a degree, in chemical
union with the alumina and silica in the clay to form a
dense and durable mass.  A kiln is a furnace or oven in
which brick are fired or heat treated to develop hardness.
Where brickmaking is done on a large scale, the firing
operation is performed in a continuous-process kiln referred
to as a tunnel kiln.  In making brick on a small
scale, firing is a periodic operation wherein the brick
are placed in the kiln, the fire started and heat developed,
and then, after several days of firing, the fuel is cut
off from the fire and the entire kiln and its load are
allowed to cool down naturally.   Where brickmaking is on
a high production basis, the kiln is the largest single
investment for the manufacturer.   It can represent a cost
of as much as a half million dollars.   For our purposes,
we will concern ourselves with the periodic-type kiln.
We will limit our attention to kilns which can be built
of locally available material and can be fired with fuels
native to the land.
 
    To reduce the kiln to its simplest parts, we will
identify the different components as follows:
 
            The Fire Box, The Flue System, The
            Permanent Side Walls and the Mudded
            End Walls                     
 
    The fire box is an opening through which the operator
feeds the fuel.  It generally consists of an opening
about 24 inches wide and 38 inches high and 30 inches
deep.  The top area can be arch-shaped, but this is a
refinement which is not necessary.   In the center of the
24-inch span, about 20 inches from the ground, iron rods
or grid bars are placed.  These bars, preferably 3/4 inches
in diameter, are spaced about 3 inches apart and are to
serve as a grate in the opening of the fire box.   They
are secured by embedding them in the brick work on either
side of the opening.  See detail in Illustration No. 4.

52p12a.gif (600x600)


 
    The flue system is the system of open spaces purposely
made in stacking the brick to allow the movement of heat
and gases.  The flue system provides openings for the
heat from the fire box to reach the brick in the kiln
and to travel to the upper areas of the kiln in the same
manner as smoke and heat will travel up a chimney.   The
flue system is, then, a chimney built in the kiln of the
brick to be burned.
 
    The permanent side walls are made of previously fired
brick which form the two sides of the kiln.   The fire boxes
are located in the permanent side walls.   Both side walls
are identical.  They are generally about 10 feet apart
and are perfectly parallel.  The brick to be fired are
placed in the area between the permanent side walls.   Permanent
side walls are normally two brick lengths or 20 inches
thick.  See Illustration No. 5.

52p14a.gif (600x600)


 
    To those confronted with the task of building such a
kiln, the thought may occur, "Just where do I get brick
to make the side walls and the fire boxes?" The answer
is simple.  One would start with "green" or unfired brick
and make the entire kiln, side walls and fire box.   The
first kiln would be greatly reduced from the size of the
projected kiln.  After the first firing, perhaps as many
as 50% of the brick in the kiln will develop enough hardness
to be used.  These are set aside and continued firings
with the small scale kiln are made until sufficient
brick to make the two full-sized side walls are accumulated.
 
    The Mudded End Walls are closures of brick which are
constructed at the ends-of the permanent side walls.   The
mudded End Walls may be made of previously burned brick
or they may be built up of unburned brick.   It is through
the openings closed by the Mudded End Walls that the brick
are loaded into the kiln and removed from the kiln's
mid-section.  Illustrations 5 and 6 will serve to show the

52p14a0.gif (600x600)


layout and construction of the fire boxes, the permanent
side walls and the mudded end walls.   The mud for the end
walls is a mixture of brick clay and water which is smeared
on the outer areas of the brick placed between the permanent
side walls.  This mud is smeared on by hand in a
fashion much like the modern day plasterer would spread
plaster on a house wall.  The purpose of the "plastering"
mud is to prevent the development of flues or escaping
heat from the kiln as it might travel through cracks between
brick set in the ends of the kiln.   Brick fired in
this end area are seldom exposed to the heat necessary to
develop desired hardness and, for this reason, they are
set aside to be placed in the inner kiln areas on subsequent
firings.
 
    Let us assume that the brick to be processed as burned
building units have been thoroughly dried and that the
permanent side walls of the kiln, together with the archway
fire boxes, have been prepared for loading and subsequent
firing.  The dried brick are first arranged in
the area immediately in back of the fire box.   The placing
of brick is always BETWEEN the permanent side walls.
Brick in the fire box area are placed one on top of the
other in a cross hatch manner.   Thus, two brick would be
placed on the ground in back of the fire box and two more
will be placed on top of these but turned 90 [degrees] so that
they overlap the bottom two brick.   This process continues
until the entire area is filled.   Bricks in the inner
section of the kiln are never placed in close proximity
one to the other.  This is to permit the heat to make
thorough penetration of the mass of brick and to permit
gases generated during the firing process to escape.
There are two exceptions to the rule about placing brick
close to each other.  In the case of the brick appearing
in the end zones of the kiln, it is recommended that these
units be placed close to each other.   This is the area
where the end wall mud is applied and it is not desirable
to permit the development of a flue area through the end
walls.  The other area where brick are close-set is the
last course of brick at the top of the kiln.   In laying
or placing the top-most row of brick, the operator will
place the brick wide-spaced to form areas about 2 feet
square in a number of places across the top of the kiln.
Thus, when looking down on the top of a properly placed
kiln, one would see the two permanent side walls and he
would see a number of square areas in which the brick were
open placed or separated.  The number of these top openings
depends on the size of the kiln.   Illustration No. 6

52p15a.gif (600x600)


shows a typical arrangement.   As in the case of the end
walls, the close-set top brick are mudded over to prevent
the escape of gases and heat through cracks between brick.
It is now obvious that we have established a flue system
or draftway extending from the fire box, through the setting
of brick and extending onward through the kiln setting to
the top of the kiln itself.  It is at this point that we
apply one set of firing controls required on the kiln.
Pieces of sheet metal should be provided to slide over the
various openings to control the amount of hot air and
gases as they pass out of the open set flue space.   Thus,
a piece of sheet metal about three feet square should be
provided for each 2' x 2' opening in the top of the kiln.
To create a greater draft and to get the fires burning
more rapidly, the flue covers would be removed.   To dampen
the fires and to hold the heat as long as possible (known
as fire soaking) the draft covers would be slid over the
openings and thus retard the passage of gases and heat
from the kiln.
 
    Special attention is drawn to the cross hatch manner
in which brick are stacked, one on the other, to accomplish
the flue system mentioned above.   The basic structure is
the same as that outlined for the drying stack earlier.
The same tie or key system is adhered to.   The keying
technique, in the inner brick placing area is extended
two directions.  In order to prevent internal topple or
insecure and unstable piling of brick, the rows are keyed,
one to the other, by placing the second row of brick in
close proximity (actually about one-half inch short of
touching) the brick in the first column.   The brick so
placed are set so that a side of the brick in the second
column will be placed against the ENDS of the brick in
the first row.  This setting is reversed in the case of the
second stand of brick and so on until the entire kiln is
loaded and thoroughly tied in, row with column, etc.   See
Illustration No. 7 for details of row and column placing.

52p17a.gif (600x600)


 
    The selection of fuel is frequently limited to just
what burnable materials are on hand.   Wood is the most
likely fuel and is perfectly acceptable in creating the
high heat necessary for complete burning of the kiln.
The wood should be cut in lengths of about 6 feet.   It is
placed on top of the grate bars and extends into only the
inner edge of the permanent side walls.   The wood is pushed
inward as the ends are consumed.   Other than wood, fuels
which have been used successfully to burn brick in various
countries include coffee husks, coconut hulls, dung, olive
pits, and even burnable fabric scraps.   Sufficient fuel
in a "ready-to-go" condition should be in good supply
whenever the firing process is started.   It would be conceivable
that the operator short of fuel would lose his
entire load of brick due to under firing if the fires
were allowed to die down and go out simply because sufficient
fuel was not on hand to complete the firing operation.
 
    As mentioned above, when the firing is about to start,
the operator places the wood or other fuel on top of the
fire box grate bars.  Then he starts a small fire directly
under the grate so that the flames traveling upward
will ignite the fuel on top of the grate bars.   The flue
covers on the top of the kiln would be left open to permit
free access of air and to create a draft from the fire
box, through the fire, and on upward to the roof of the
kiln.
 
    The principal part of the burning is done on top of
the grate bars.  The under area provides a point of entry
for the air (oxygen) required to accomplish continued
combustion.  This under area can be closed off by placing
excess fuel or ashes in the under area.   This dampering
by closing off the area under the grate is still another
control feature.  The early stages of firing, when the
fires are just getting started and developing heat, would
be conducted with the dampers on top open and the under
grate area free of fuel or ash.   After ten to twelve hours
of continued burning and stoking, the inner portion of
the kiln will begin to pick up heat.   The operator may be
able to discern a slight reddish glow as he observes the
inner portion of the kiln by looking through the archway
of the fire box.  When the entire inner mass of the kiln
has developed a cherry red glow, the kiln is at its prime
heat for good firing.  At this time, however, the hot
areas may be confined to just those brick in or near the
flue path.  In order to complete the firing and to permit
the inner portion of all the brick to attain proper heat,
it is best to retard the draft movement by sliding the
top covers over about half of the flue openings.   At
the same time, it is advisable to place fuel or ash in the
bottom grate area.  This retardation of draft reduces the
heat loss through the stack and permits the heat to travel
in the areas of the brick setting not reached via the normal
draft or flue routes.  This period of dampered fire box and
upper flue tops is known as the "soaking" period.  Soaking
in the firing of brick is very important.   Once the cherry
red inner hue (corresponding to a temperature range of
1600 [degrees] F - 1750 [degrees] F., 875 [degrees] C - 900 [degrees] C.) is developed and the
soak period started, it is necessary for the operator to
hold this condition for at least 6 hours.   During this
six hour "hold", fuel will be consumed and should be
applied to the fire.  The combustion will, however, be
retarded as the passage of air is reduced.
 
    After the six hour "hold" period is completed, the fuel
is cut off and the top plates are placed in position to
cover the flue openings.  Often the openings in the
permanent side wall or the fire box will be filled with
ashes from previous fires.  The reason for this is to prevent
any heat loss due to the open grate way and thus hold
the heat in the kiln and on the brick as long as possible.
This covering of flues and closing the fire box may be
thought of as an extension to the soaking period.   After
about two days, the brick can be removed from the kiln.
The end walls are torn down by removing the upper section
first.  The brick which formed the actual end wall and did
not receive full benefits of the heat can be refired in
subsequent firings.  The mud used to close up the gaps
between close set brick will knock off and will not impair
the appearance of the brick.   After all brick are
removed from the area between the two permanent side
walls, the entire kiln, with the fire boxes included,
should be swept clean of refuse and bits of clay and broken
brick.  The kiln is now ready for another firing.
 
    One final word concerning the firing operation should
be included at this point.  When clay products are processed
through the firing or heat treating stage, they
undergo an important transition:   shrinkage.  Normally the
shrinkage of a fired clay product will amount to as much
as ten percent of its original size.   Thus, in firing a
kiln loaded with brick, we should be aware of the shrinkage
factor and expect the stacking of brick in the center
of the kiln to be several inches lower after the firing
process than it was at the beginning.   Some kiln operators
will be able to judge the degree of firing by noting the
height to which the pile of brick has been reduced as a
result of this normal function:   shrinkage.
 
    Building brick, as noted here, can be made with clay
and locally available fuels.   The labor required is hard,
and by our terms, backbreaking.   The rewards, on the other
hand, are enormous.  Durable housing which will resist
the torments of the elements generates a feeling of
purposefullness and security to those so sheltered.   The
comfort of living in a dry abode and one which will remain
cool in the hot sun should be reward enough for the hard
work involved.
 
    For the PCV who strikes out on his own, and attempts
to build and operate such a kiln and product as is described
here, the author has one additional ingredient
to suggest:  patience!!
 
    Haste in building the kiln can result in shoddy side
walls, shoddy side walls and fire boxes means that constant
and time consuming repairs are called for.   Haste in
placing the brick in the kiln can result in collapse of
the entire mass.  The net result here is dead loss in
most cases.  Perhaps the most critical area to exercise
patience is in the drying process.   Brick with even a
trace of water should never be placed in the kiln.
 
    Questions and comments will be welcomed by the author.
Inquiries and related comments should be directed to:
 
                D. W. THOMAS
                39 WOODBRIDGE AVENUE
                UNIT 23
                METUCHEN NJ  08840
                USA
 
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