2. BRICKS
Bricks have been used for all types of construction from
the olden days.
Usefulness of brick has not reduced even though better
materials like cement, steel and other materials have
already came into use.
It is known that bricks are made from soil (clay).
Hence the properties of the brick depends on the soil
properties.
Good quality brick cannot be made from all types of soils.
Analysis of soil to be used in manufacture of brick can be
divided in to 3 parts.
3. Composition of good brick earth
Constituents of a Brick
• Alumina
– Chief constituent of all kinds of clay
– Imparts plasticity to clay so that it can be moulded
– A good brick should have 20-30% of alumina
– If in excess, it makes the brick warp and crack on drying
and burning
• Silica/sand
• A good brick earth should contain about 50-60% of
silica
– It imparts uniform shape to bricks
– Its presence prevents cracking, shrinking and warping of
raw bricks
– The durability depends on proper proportion of silica
– Its excess destroys cohesion between particles and makes
the brick brittle
4. • Lime
– It should be present in very small quantities not exceeding 5%
– It helps in fusing sand(alone infusible) which then acts as
cementing material for brick particles.
– It should be very finely powdered else on burning the lumps will
convert to quicklime which expands in presence of moisture
resulting in splitting of bricks.
– The excess of lime causes the brick to melt and loose its shape
• Oxide of iron
– It is added in small quantity – 5-6%
– It helps fuse sand
– Imparts red color to brick on burning
• Magnesia
– A small amount of MgO imparts yellow color to the brick
– It decreases shrinkage
– Its excess leads to decay of brick
5. Raw material clay
• Clay is one of the most abundant natural mineral
materials on earth. For brick manufacturing, clay
must possess some specific properties and
characteristics.
• Such clays must have plasticity, which permits them
to be shaped or molded when mixed with water;
they must have sufficient wet and air-dried strength
to maintain their shape after forming.
• Also, when subjected to appropriate temperatures,
the clay particles must fuse together.
6. Types of Clay
• Clays occur in three principal forms, all of which have
similar chemical compositions but different physical
characteristics.
– Surface Clays: Surface clays may be the up thrusts of older
deposits or of more recent sedimentary formations. As the
name implies, they are found near the surface of the earth.
– Shales: Shales are clays that have been subjected to high
pressures until they have nearly hardened into slate.
– Fire Clays: Fire clays are usually mined at deeper levels than
other clays and have refractory qualities.
– Surface and fire clays have a different physical structure
from shales but are similar in chemical composition.
7. – All three types of clay are composed of silica and alumina with
varying amounts of metallic oxides.
– Metallic oxides act as fluxes promoting fusion of the particles at
lower temperatures. Metallic oxides (particularly those of iron,
magnesium and calcium) influence the color of the fired brick.
– The manufacturer minimizes variations in chemical composition
and physical properties by mixing clays from different sources and
different locations in the pit.
– Chemical composition varies within the pit, and the differences are
compensated for by varying manufacturing processes. As a result,
brick from the same manufacturer will have slightly different
properties in subsequent production runs. Further, brick from
different manufacturers that have the same appearance may differ
in other properties.
8. Manufacture of clay bricks
1. Preparation of brick clay
– Unsoiling, Digging , Cleaning, Weathering , Blending ,
Tempering
2. Moulding the bricks
– Hand Moulding , Machine Moulding
3. Drying the bricks
– Natural , Artificial
4. Burning the bricks
– Burning in clamps, Burning in kilns
12. After that pour the water slowly in the soil and go on mixing it so that
the soil becomes plastic.
The consistency should be such that it can be molded easily. Amount of
water should not exceed otherwise moulding becomes difficult.
Take a handful of mixing soil make a ball by pressing it.
If necessary little amount of water is added to it make it the ball.
Keep the ball under the sun for drying. When the has dried see that
weather the ball has lost its shape or not.
Also examine if there are any cracks on the surface.
The ball which does not get deformed on drying and has very less cracks
on its surface, is most suitable for manufacture of bricks.
13. If the soil is having more sand it can be powdered easily after
drying such soils are not suitable.
The ball which after drying has become very hard and has
wide cracks, shows the deficiency of sand in soil. Such soils
can be used for manufacture of bricks by adding requisite
amount of sand.
Easy method is add some quantity of sand and prepare the ball
in each case.
Balls with all proportions of sand may be allowed to dry.
After drying inspect the balls, the ball which has the least
amount of cracks gives the most suitable proportions of sand.
14. Moulding properties of sand : if the corners and edges of
the bricks are not well formed then the mixture contains
less quantity of water.
Hence, add some more water in such case make another
brick.
Repeat this process till we get formed bricks have all
molded bricks for drying.
Shrinkage test of soil :
The extent of deformation and shrinkage of bricks after
burning can be determined from this test.
15. Burn the sample brick in the potter kiln for 3 days and 4
nights.
Bricks should be burnt up to red hot.
Actually the time for burning the brick depends on the size and
shape of the brick.
Bricks should be kept in the kiln in such a way that some
space is left b/w them. This is essential for proper burning.
After burning of the brick allow the brick to cool , then remove
from the kiln and examine them for shrinkage and
deformation.
Sort out the brick which have lost their shape.
Those bricks which have shrunk evenly and have
not lost shape should be selected for further tests.
16. Determination of strength and quality of
bricks:
Strike the flat surface of two bricks if the sound produced
is a metallic one then the bricks are of good quality.
If the sound produced is dull then the bricks are not of
good quality.
Strength of bricks can also be found out by soaking the
same in water.
Soak the bricks in water for 24 hrs.
Bricks of good quality do not absorb water more than 1/8th
to 1/6th of their own weight.
Compressive strength of good bricks should not be less
than 35 kg/sq.cm
17. Manufacture of Bricks :
There are four processes in the manufacture of bricks.
1. Preparation of soil
2. Molding of bricks
3. Drying of bricks
4. Burning of bricks
18. 1. Preparation of soil for brick making :
After the selection of site, grass, roots of trees etc
should be removed from that place.
If there are any stones and boulders, they should
be thrown away. In fact 10 to 15 cm of top layer
should be completely strapped.
After that soil dug by means of spade or anything
else.
The earth is broken in to pieces, the loose earth is spread out in
heaps 1 to 1.5 m high for weathering. Care should be taken to see
that there are no stone pieces are left in the earth.
2 cubic meter of soil is required for 1000 (20 x 10 x 10 cm) bricks.
After monsoon again the earth is dug out from heaps.
19. If necessary, sand is also mixed in the powdered
natural soil. After that they are thoroughly mixed.
This process is known as Blending.
After Blending, requisite amount of water should
be added in the soil and the same is kneaded by
feet of men or animal. This process is known as
tempering.
Amount of water to be added with soil is
determined by test. Quantity of water should not
be in excess otherwise the slope will be reformed
after drying.
Tempering must be done very carefully so that the
soil becomes plastic and mixing is uniform.
In large quantity of bricks are to be made , then
pug mill is used for kneading.
20. Pug mill : (for large
kneading)
It consists of a conical
upright cylindrical of steel
whose height is 1.5 to 2.0
m. cylinder is normally
tapered and 60 to 75 cm of
its depth remains buried in
the ground.
There is a vertical shaft in
its center which can rotate.
Horizontal blades are fixed to the
shaft. There are many wedge
shaped knives in the horizontal
blade which are made of steel.
21. 2.Moulding of bricks :
Moulding of bricks can be done by
means of mould.
Mould is a rectangular box, in which
top and bottom portion remains
open.
Clay and water are placed in the pug mill from
top and shaft is turned either by bullock or
mechanical power.
The blades goes inside the soil and soil will be
kneaded by knives.
Finally well kneaded soil comes out from the
bottom portion of the pug mill through
aperture.
Pug mill works continuously. Kneaded soil is
serried for molding to other place.
22. Mould is made from strong wood and iron
plates are filled are the edges so that wear
and tear of the mould is very little.
Metallic moulds are superior to wooden
moulds.
Mainly mould is made for one brick, but
now a days a new type of mould has also
come in practice. By means of this mould,
five bricks can be moulded at a time.
Size of mould depends up on the size of
the brick. But size of mould in all directions
should be larger by 8 to 10% as compared
to the size of the brick so that effect of
shrinkage due to drying and burning can
be compensated.
23. Hand moulding
• Moulds are rectangular boxes of wood or steel,
which are open at top and bottom. Steel moulds
are more durable and used for manufacturing
bricks on large scale as shown in figure.
Bricks prepared by hand moulding are of two types.
a) Ground moulded bricks
b) Table moulded bricks
25. 3.Drying of bricks :
Bricks are dried in the sun after molding. Bricks after
moulding when dried enough to be handled safety are
carried to the drying yard.
Drying yard must be situated in the yard.
Stacking is done by keeping the bricks on
their edges. There are 8 to 10 bricks in each
row. There should be enough space between
the rows so that proper circulation of air.
26. Sometimes roof is provided, so that rain should not destroy
the bricks.
it takes about 8 days for drying of bricks some times bricks
may be artificially dried by hot gases from kilns.
Bricks are sent for burning after drying.
One should see carefully that bricks have dried fully
otherwise moisture from wet brick may spoil the surface of
the other bricks while burning.
27. Newly-formed bricks are dried under shelters
in a natural way.
When the bricks are
almost dry, they are set
vertically in order to
make room for the next
batch of bricks.
28. 4.Burning of bricks :
Burning of bricks must be done carefully because under
burnt bricks remain soft. Bricks are burnt in the kilns.
Mainly kilns are of 3 types.
i. Pajawa of clamp or open kiln
ii. Semi continuous kiln
iii. Continuous kiln.
i. Clamp :
Clamps are of different types and they are made in different
ways in different provinces.
A temporary clamp has been shown in figure by means of
which 1800 bricks can be burnt.
29. Bricks are arranged in clamp in a specified manner.
If the bricks are arranged length wise in one row then the other are
kept on their edges. This order should be repeated in alternate
rows. Bricks should be arranged in such a way that space for burning
fire is left in the middle.
Top most brick is to be kept vey close to each other so that roof of
the clamp is formed. Small holes must be left in the roof so that fire
can burn and may go out.
The outside of the clamp should be covered with a layer of soil 20
cm thick so that heat may not get wasted.
30. Dampness from the bricks is expelled after burning of fire due to heat and
consequently bricks shrink. When top most brick has shrunk, it means
that the dampness of the brick has been driven out.
After that top portion of clamp should be covered with a layer of soil 2.5
cm thick so that heat does not go waste.
Clamp burning
• Advantages
(i) The bricks produced are tough and strong because burning and cooling
are gradual
(ii) Burning in clamps proves to be cheap and economical.
(iii) No skilled labour and supervision are required for the construction of
clamps.
• Disadvantages
(i) Bricks are not of required shape
(ii) It is very slow process
(iii) It is not possible to regulate fire in a clamp
(iv) Quality of brick is not uniform
36. It is essential to keep some holes in the roof for the proper
burning.
It takes about 10 days for burning the bricks. After 10 days the
layer of soil may be scratched to see whether bricks burnt
nicely or not.
If the bricks have not burnt well then firing should be
continued. Clamp is allowed to cool firing 15 to 20 % of bricks
are wasted in such type of clamp.
37. Intermittent up-draught clamp :
The type of clamp is in the form of a rectangular house
with thick side walls.
At each end there is a wide door. Bricks can be taken in
or carried out through these doors.
In case of necessity temporary roof of lighter materials is also
combined so that bricks are not spoiled due to accidental rain.
The roof is removed as soon as clamp is fired.
The length, breadth and height of such type of clamp is
approximately 1.5, 3.5 and 4.0 m.
39. BULL’S TRENCH KILN :
Bull’s trench kiln is circular or elliptical in plan. A trench is dug by
taking out soil from the ground.
The depth varies from 1.5 to 2.25 m. Bricks are arranged in
the kiln in such a way that some space is left between them.
These spaces cat as fuel path in the lower portion. Fuel hoes
are provided over the fuel a an interval of 90 cm through
which fuel can be given.
Bull’s trench kiln is not loaded at one time but the kiln is
loaded in sections. The length of one section is about 3.6m
A clear space of 15 cm is left between the sections over which
chimney can be placed.
After loading one section with brick, it is covered with ashes
and soil so that heat may not escape.
When brick of one section is being burnt, hot gases enter into
the next section.
40. Bulls trench kiln seen from the loading end
Design of a Bulls trench kiln
Fired bricks being drawn from the kiln
A canvas prevents air from entering the kiln from the wrong end
A Bulls trench kiln with a fixed chimney
41.
42. In this way preheating of next section takes place.
At the end smoke goes out in the atmosphere through
chimney.
It takes about 24 hrs in burning the brick completely. When
one section has been burnt fully, then fire is advanced to
next section and the burnt section is allowed to cool.
In this way process of burning, pre heating and cooling
continues to different sections of the kiln.
When one section is being burnt, another section is being
pre heated and some other section is being cooled.
This kiln can not work in rainy season.
43. Hoffman’s Kiln :
Hoffman’s kiln is circular in plane.
Chimney placed at the center of the kiln and there are
twelve chambers around the chimney. Each chamber has
a gate so that one can communicate from outside.
Hoffman’s kiln can work continuously and hence hot gas
is always utilized. The length, breadth and height of
hoffman’s kiln is 11X4.5 X 2.5 m.
About 25000 bricks can be burnt in one chamber.
In this way 3 lakh bricks can be burnt in 12 days.
80-90 lakh bricks can be burnt per year in this kiln.
45. Advantages :
Considerable economy in fuel.
Burning is uniform and there is proper control of
temperature.
Bricks can be sent at construction site in planned way.
%age of first class bricks is more.
46. II group :
Compressive strength test
Weathering test
Qualities of good brick and their tests :
Bricks of good quality should be used for construction. Tests are
necessary to identify bricks. Tests can be divided into two groups.
Those tests which can be performed anywhere and special
apparatus is not necessary.
Those tests which can be performed only in the laboratory.
I group :
1. External appearance
2. Hammer test
3. Hardness test
4. Absorption test
5. Specific gravity
6. Efflorescence
47. External appearance :
The slope of a good brick should be
uniform and regular and their edges must
be sharp.
There should be no cracks, air bubbles,
lime nodules or pebbles in the bricks.
The degree of burning can be estimated
from the color of brick, although some
times color of brick misleads estimation.
Surface of brick must be plane but neither
it should be very rough nor very smooth.
Degree of burning of brick should be
neither be less nor more. Over burnt
bricks, known as Jhama bricks, become
useless for construction work. In fact due
to high temperature Jhama brick melts
and hence it loses its shape.
48. 2. Hammer test :
When well burnt brick (having no cracks) is hit by
hammer, then metallic ringing sound is produced. Such
type of bricks are called 1st class bricks.
If two 1st class bricks are struck against each other, then
they produce metallic ringing sound.
A 1st class brick will not break if it is dropped from a
height of 2 to 5 m.
49. Hardness test :
if the surface of a good brick is searched by the nail of a
finger, no mark should be left on it. Estimation of
hardness can also be done breaking the brick with
hammer.
Under burnt brick will break easily where 1st class brick
will not break easily.
50. Absorption test :
The amount of absorption of water is a good indication of the degree of burning
of brick.
The brick is immersed in water for 24 hrs. due to this the weight of brick
increases.
After weighing the wet brick the percentage of absorption can be found out.
If the percentage of absorption of water is 16% then these can be used for
construction.
% of water absorption of 1st class brick varies from 12 to 16%. If the brick is to
be used fro hydraulic work, then percentage of absorption should be less than
6%.
High % of absorption indicates insufficient burning.
The permeability of brick is of extreme importance in case of exterior walls. If
the permeability is high then rain water will penetrate in to the walls.
51. Specific gravity :
Other factors being constant, higher the specific gravity of the brick more is
the strength of the brick.
Unit weight of ordinary bricks should be 1600 to 1920 kg/cu.m
Efflorescence :
main cause of decay of bricks is the crystallization of soluble salts.
Salts are
magnesium sulphate,
calcium sulphate,
sodium and potassium sulphate etc.
Being soluble in water these salts are deposited on the brick surface as
efflorescence as a result of wetting and drying of the brick by rain and sun
by rise and fall of water table.
52. Test :
Take distilled water in a shallow vessel and dip one end of brick in water
by about 2.5 m.
If there will be efflorescence then salt will be deposited on brick otherwise
not. Test takes about 5-7 days.
Use of high lime mortar is practiced for reducing efflorescence some times
damp proof course is also given.
53. Compressive strength :
durability of brick can be estimated from the results of
compressive strength. Classification is also done
according to compressive strength.
Weathering test :
weathering test should also be cone in the laboratory
to see its effect on brick.
54. Defects in bricks :
1. Over burning of bricks : Due to over burning, bricks lose their
shape. These bricks are called Jhama Bricks. These are unsuitable
for building construction.
2. Under burning of bricks : the compressive strength of the under
burnt brick is less and the degrees of absorption of water is more.
Under burnt bricks should not be used.
3. Bloating : swelling of bricks takes place due to the presence of
excess of------
a. carbonaceous matter and
b. gas forming material in the clay
c. due to bad burning or very rapid firing.
55. 4. Black core: this defect occurs where clays are heated for rapidly in the
kilns causing the surface to vitrify and the interior to remain black.
5. Efflorescence : bricks containing a relatively large proportion of soluble
salt, liable to become discovered by the formation of whitish deposit.
6. Lamination : laminations are caused by air in the voids of clay. They
produce thin lamine on the faces of bricks which swell off on exposure to
weather.
7. Lime nodules : if particles of the stone are left uncrushed during
preparation of clay, then become lime nodules in bricks. These lime
nodules will expand when water is absorbed thus causing disintegration
of bricks. Wide cracks in walls develop due to this.
56. Point of
comparison
Continuous (or) semi continuous kiln Clamp
Initial cost The initial cost of Bull’s trench kiln or
Hoffman’s kiln is higher. Suitable for big
scale of manufacture of bricks
Low and hence suitable for burning
of small quantity of bricks
Cost of fuel Fuel consumption is very low in such
type of kiln because heat is not wasted.
High, heat is lost from top as well as
sides. Hot gases are not used.
Control of fire There is complete control on five and
even raw bricks can be burnt after pre
heating
There is no control over fire. At
some places temperature is high
and others low.
Supervision Supervision by skilled labor is
necessary.
Once fixed no supervision is
required.
Time of
burning and
cooling
It takes 24 hrs in burning the bricks and
12 days in cooling.
Time required is 2 months to 6
months
% of first class
bricks
90% first class bricks can be obtained
from such type of kilns
Not more than 60% are produced
Qualities of
brick
Quality if all bricks are uniform.
Warping does not take place
Quality of bricks are not uniform
57. Uses of bricks :
Bricks are mainly used for the construction of walls.
Bricks when molded in the shape of a gutter can be
used as drains.
Bricks with cavities known as hollow bricks can be used
for insulation purpose and because of this light weight
they are more useful in speedy construction.
58. Paving bricks prepared from clay containing high
percentage of iron can be used for pavements, since they
resist abrasion in a better way.
Bricks with the holes are used in multi storied framed
structures.
Sand-lime bricks are used for ornamental work.
Fire bricks made of fire clay can be used as a refractory
material.
Bricks are used in the construction of the compound
walls, columns etc. broken pieces of bricks are used as in
the facing of wall.
Bricks are used in the construction of chimneys and other
special works.
59. Qualities of good bricks :
Bricks should have perfect edges, well burnt in kilns,
copper colored, free from cracks with proper rectangular
shape and of standard size (19 x 19 x 9 cm)
Bricks should give clear ringing sound when struck with
each other.
Bricks must be homogeneous and free from voids.
The percentage absorption of water by weight should not
be greater than 20% for 1st class and 22% for 2nd class
when soaked in cold water for 24 hrs.
Bricks should be sufficiently hard i.e., no nail impression
must be present when scratched. The average weight of
brick should be 3-3.5 kg.
60. Bricks should not break when dropped from about 1 m.
Bricks should have low thermal conductivity and should
be sound proof.
Brick should not show deposits of salts when immersed
in water and dried.
The minimum crushing strength of brick must be
3.5 N/sq.mm
Classification of bricks :
Bricks are classified based on the manufacturing process
adopted. The classification is given as follows.
61. 1st class bricks are table-molded and of standard shape. These
comply with all good qualities of bricks and are used for
superior and permanent works.
2nd class bricks are ground-molded burnt in the kilns. The
surface of the such bricks are rough and are slightly irregular
in shape. Such bricks are used with coat of plaster.
3rd class are ground-molded and are burnt in clamps. These
bricks are not hard but rough with irregular and distorted
edges. These give a dull sound when struck with each other.
They are used for un-important and temporary structures and
at places where there is less rain fall.
Over burnt bricks with irregular shape and dark colour are
classified as 4th class bricks. These are used as aggregates for
concrete in foundations, floors, roads etc.
62. Dimensions of the Bricks
• Bricks are made in traditional size and also in
metric size prescribed by Bureau of Indian
Standards. The bricks of latter size are also called
Modular bricks.
• Depression made at the top of a brick is called
the Frog
• Brick work is constructed with the frog laid facing
upwards.
• It serves to place the name of the manufacturer
and also a key to the mortar to bond bricks
together.
63.
64. • Note:
• There are depressions provided in the face of the bricks.
• There are 2 reasons for the provision of frogs
• To form a key with mortar to prevent sliding of the bricks
of the beds.
• To reduce the weight of the brick and hence economy in
the cost of transport
The prescribed actual dimensions and nominal dimensions
as per IS is given in the following table
Size Ordinary bricks Tile bricks
Metric (cm) FPS (inch) Metric (cm) FPS (inch)
Actual 19 x 9 x 9 8 (7/8) x 4 (3/8) x 2 ¾ 19 x 19 x 4 8 (7/8) x 4 (3/8) x
1 ¾
Normal 20 x 10 x 10 9 x 4 ½ x 3 20 x 20 x 4 9 x 4 ½ x 1 ¾
65. • Normal size of brick is the size including
thickness of the mortar.
• The thickness of the mortar in the brick
work should not exceed 10 mm (3/8”)
• Bricks of thickness less than normal are
called tile bricks.
• Metric bricks are also known as modular
bricks.
Conventional and specially shaped bricks :
The usual type of bricks made are shown in
figure.
66.
67. Many specially shaped bricks like
• single bull nose: the bricks with one edge rounded.
• double bull nose: the bricks with two edges rounded.
• curved bricks
The size of modular bricks are generally kept a little larger
to specified size.
DEFINATIONS:
68. • Course : a complete layer of bricks laid on the
same bed.
• Frogs : depressions provided in the face of the
bricks.
• Bed : the bottom surface of the brick when it
is laid flat
• Stretcher : the side surface of the brick visible
in elevation when the brick is laid flat
• Header : the end surface of the brick when it is
laid flat
• Arrises : the edge formed by the intersection
of plane surfaces of a brick
• Perpends : these are vertical joints between
bricks either in longitudinal or cross directions.
Also known as cross joints
