3. Bricks are rectangular in shape and can be easily handled with one hand.
Bricks may be solid, cored, hollow or frogged.
Standard Brick Size : 9” x 4 ½’’ x 3’’
Custom-shaped bricks are often required for building for providing special
details.
Weight of the a standard brick is 3.0 kg.
Frog is provided to form key for holding the mortar and therefore the bricks are
laid with frogs on top. Frog is not provided in 4 cm high bricks and extruded
bricks. The size of the frog is 10 x 4 x 1 cm.
4. Classification of bricks
Clay bricks are classified as first class, second class, third class and fourth class
based on physical and mechanical properties.
First class bricks
1. They should be smooth and rectangular, with parallel, sharp and straight edges
and square corners.
2. Thoroughly burnt and are deep red, cherry or copper colour.
3. Free from flaws, cracks and stones.
4. Uniform texture.
5. Should not have any impression or scratch.
6. When two bricks are struck against each other a strong metallic or ringing sound
should be heard.
7. Water absorption should be 12 to 15% of its dry weight when immersed in cold
water for 24 hrs.
8. The crushing strength should not be less than 10 N/mm2.
Uses: Exposed brick work
Flooring
Reinforced brick work.
Pointing
On field practise:
5. Second class bricks
1. Small cracks and distortions are permitted.
2. Water absorption should be 16 to 20% of its dry weight.
3. The crushing strength should not be less than 7 N/mm2.
Uses: Hidden masonry works, Centering of Reinforced brick work.
Reinforced cement concrete structures.
Third class bricks
1. Under burnt and are soft and light coloured.
2. Water absorption is 25% of its dry weight.
3. Produces a dull sound when struck against each other.
Uses: Temporary building structures.
Fourth class bricks
1. Over burnt and badly distorted in shape and size.
2. Brittle in nature.
Uses: Foundation and Floors in lime concentrate and road metal.
6. On Strength:
1. The Bureau of Indian Standards has classified bricks on basis of compressive
strength.
2. Bricks having compressive strength of more than 40 N/mm2 are known as
heavy duty bricks.
Uses: Bridges, multi-storey buildings etc..
On the Basis of Use:
Common Brick
1. They are manufactured economically without special reference to appearance.
2. They have great strength and durability.
3. Used for filling, backing and in walls where appearance is of no consequence.
Facing Brick
1. They are made to have good appearance, either of colour or texture or both.
2. Durable under severe exposure.
3. Used in front of building walls.
Engineering Brick
1. Strong, impermeable, smooth, table moulded, hard and conform to defined
limits of absorption and strength.
2. They are used for load bearing structures.
7. On the Basis of finish:
Sand-faced Brick
1. Has textured surface
2. Manufactured by sprinkling sand on the inner surfaces of the mould.
Rustic Brick
1. Has textured finish, varying in patterns.
On the Basis of Manufacture:
Hand made
1. Bricks are hand moulded.
Machine made
1. They are wire cut bricks, pressed bricks, moulded bricks.
8. On the Basis of Burning:
Pale Bricks
1. Under burnt bricks obtained from outer portion of the kiln.
Body Bricks
1. Well burnt bricks obtained from central portion of the kiln.
Arch Bricks
1. Over burnt bricks obtained from inner portion of the kiln.
On the Basis of Types:
Solid
1. Small holes not exceeding 25 % the volume of the brick, frog not exceeding
20 % of the total volume
Perforated
1. Small holes may exceed 25 % the volume of the brick.
Hollow
1. Small holes may exceed 25 % the volume of the brick.
Cellular
1.Holes closed at one end exceed 25 % the volume of the brick.
9. Characteristics of Good Brick
Size and Shape – uniform in size and shape
Colour – deep red or cherry colour
Texture – should not be too smooth. Should have uniform texture
Hardness and Soundness – When scratched by finger
nail no impression should be made. When two bricks are struck against
each other a metallic sound should be produced.
Water Absorption – should not exceed 20% of its dry weight.
Crushing Strength – Should not be less than 10 N/mm2
10. Ingredients of Good Brick Earth
Silica (sand) - It imparts uniform shape to bricks. Its presence prevents
cracking, shrinking and warping. Its excess destroys cohesion between
particles and makes the brick brittle.
Alumina - Composition of good brick earth Alumina Chief constituent of all
kinds of clay Imparts plasticity to clay so that it can be moulded If in
excess, it makes the brick warp and crack on drying and burning.
Lime - It should be present in very small quantities not exceeding 5%. 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.
Magnesia - imparts yellow colour to the brick It decreases shrinkage Its
excess leads to decay of brick.
Iron - It is added in small quantity – 5-6% It helps fuse sand Imparts red
colour on burning when excess of oxygen is available. Dark brown or even
black colour when oxygen is insufficient. Gives strength and hardness
and increases durability.
The clay used for brick making consist mainly of silica and alumina mixed in
such proportion that the clay becomes plastic when water is added to it. It also
consist of small proportions of lime, iron, manganese, sulphur, etc.
11. Manufacturing Process of Clay Brick
1. Preparation of brick clay
Unsoiling , Digging , Cleaning, Weathering , Blending , Tempering.
2. Moulding
Hand Moulding , Machine Moulding
3. Drying
Natural, Artificial
4. Burning
Burning in clamps, Burning in klins.
If the bricks are to be manufactured on large quantities, necessary scentific test are
to be conducted to determine the suitibility of the earth.Certain materials like fly ash,
sandy loam, rice husk ash, basalt stone dust are to de added to imporve the
quality of bricks.
12. Preparation of clay:
Unsoiling :- Top layer of 20cm depth is removed as it contains impurities.
Digging: - Clay dug out from ground is spread on levelled ground ( just a little
deeper than the general level) in about 60cm to 120cm heaps.
Cleaning: -Stones, pebbles, vegetable matter, etc. are removed and lumps of
clay are converted into powder form.
Weathering:- Clay is exposed to atmosphere from few weeks to full season for
softening and mellowing. (Preferably dug before monsoon)
Blending:- Clay is made loose and any ingredient to be added to it is spread out
at top and blended by turning it up and down in vertical direction.
Tempering:- Clay is brought to a proper degree of hardness, then water is added
to clay and whole mass is kneaded or pressed under the feet of men or cattle.
For large scale, tempering is usually done in pug mill as shown in the figure.
13. Process of tempering :
Consist of a conical iron tub of height 1.2 to 1.8m. The diameter of the tub from
bottom to top may be 0.75 to 0.8m and 1.2 to 1.3m.The tub is sunk 0.6m below
ground level.
Process of tempering Clay with water is placed in pug mill from the top. When the
vertical staff is rotated by using electric pair, steam or diesel or turned by pair of
bullocks. Clay is thoroughly mixed up by the actions of horizontal arms and knives
when clay has been sufficiently pugged , hole at the bottom of tub, is opened out and
the pugged earth is taken out from ramp for the next operation of moulding .
14. Moulding:
Moulding Clay, which is prepared from pug mill, is sent for the next operation of
moulding . Following are the two ways of moulding . Hand Moulding Machine
Moulding .
Hand moulding:
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
15. a) Ground moulded bricks: ground is first made level and fine sand is
sprinkled over it. Mould is dipped in water and placed over the ground to fill
the clay. Extra clay is removed by wooden or metal strike after the mould is
filled forced mould is then lifted up and raw brick is left on the ground. Mould
is then dipped in water every time lower faces of ground moulded bricks are
rough and it is not possible to place frog on such bricks.
Ground moulded bricks of better quality and with frogs on their surface are
made by using a pair of pallet boards and a wooden block
16. b) Table- moulded bricks:
Process of moulding these bricks is just similar to ground bricks on a table of size
about 2m x 1m.
The bricks are moulded on stock boards nailed on the moulding table.
Stock boards have projection for forming the frog.
A thin mould called pallet is placed over the mould.
The mould containing the brick is then lifted off the stock board and made to rest
on the pallet. The mould is then removed and the brick is sent for drying.
17. Machine moulding:
Machine moulding This method proves to be economical when bricks in huge
quantity are to be manufactured at the same spot. It is also helpful for moulding
hard and string clay. These machines are broadly classified in two categories
(a) Plastic clay machines (b) Dry clay machines
a) Plastic clay machines: This machine containing rectangular opening of size
equal to length and width of a brick. Pugged clay is placed in the machine
and as it comes out through the opening, it is cut into strips by wires fixed in
frames, so there bricks are called wire cut bricks.
b) Dry clay machines: In these machines, strong clay is first converted into
powder form and then water is added to form a stiff plastic paste. Such
paste is placed in mould and pressed by machine to form hard and well
shaped bricks. They carry distinct frogs and exhibit uniform texture.
18. Drying:
They can be dried in open air or in artifical driers.
Artifical Driers are of 2 types : Hot floor drier and tunnel drier.
•In hot floor drier heat is applied through a furnace placed at one end of the
drier.
•Tunnel drier are heated by fuels underneath by steam pipes. They are more
economical than floor driers.
•In artifical driers temperature rarely exceeds 120 deg C.The time varies from
1 to 3 days.
In some countries bricks are dried in open air.
•They are stacked on raised ground and are protected from bad weather and
direct sunlight.
•A gap of 1.0m is left in the adjacent layers of the stacks so as to allow free
movement for the workers.
19.
20. Burning:
•This is very important operation in the manufacturing of bricks to impart
hardness, strength and make them dense and durable.
•Heating clay upto 640 degree C produces physical changes. If such clay is
cooled back, it absorbs moisture from air and gets hydrated back to its original
state. Such poorly burnt clay is unstable.
•However, if clay is heated up to 700-1000 deg C chemical changes take place
by which alumina and silica in clay fuse together resulting in a compound which
is strong and stable.
•Burning of bricks is done either in clamps or in kilns.
•Clamps are temporary structures and they are adopted to manufacture bricks
on small scale.
•Kilns are permanent structures and they are adopted to manufacture bricks on
a large scale.
Burning in Clamp :
•The bricks and fuel are placed in alternate layers.
•Each brick tier consist of 4-5 layers of bricks.
•Space is left between the bricks for free circulation of hot
gases.
•The top and sides of the clamp are plastered with mud.
•Then a coat of cowdung is given, which prevents the escape
of heat.
•The production of bricks is 2-3 lacs andf it takes 6 months to
complete the process.
•About 60% of first class bricks can be produced through this
method.
21. Kilns:
A kiln is a large oven, which is used to burn bricks underground.
1) Intermittent kilns – discontinuous burning of bricks
2) Continuous kilns - continuous burning of bricks
Intermittent kilns: These are intermittent in operation, which means that they are
loaded, fired, cooled and unloaded and thern the next loading is done.
a) Intermittent up-draught kilns
b) Intermittent down-draught kilns
Continuous kilns: These kilns are continuous in operations. This means that
loading,firing, cooling and unloading are carried out simultaneously in these kilns.
There are three types of continuous kilns.
a) Bull’s trench kiln
b) Hoffman’s kiln
c) Tunnel kiln
22. Bulls Trench Kiln
The kiln can be made circular or elliptical in shape. It is constructed on dry land, by digging a
trench, 6 - 9 m wide, 2 - 2.5 m deep, and 100 - 150 m long. Gaps are left in the outer wall for
easy assess to the trench during setting and drawing of bricks.
The green bricks to be fired are set in rows, two to three bricks wide, with holes in between
that allow feeding of coal and a sufficient flow of air through the setting.
On top of the bricks, two layers of bricks, covered with ash or brick dust, seal the setting. The
brick workers create a firing zone by dropping fuel (coal, wood, oil, debris, and so on) through
access holes in the roof above the trench. The trench contains 200 - 300,000 bricks at a time.
Small circular Bull's trench kilns use only one chimney, whereas the larger elliptical kilns need
two chimneys. Chimneys are 6 to 10 m high.
The advantage of the BTK design is a much greater energy efficiency compared
with clamp. Sheet metal or boards are used to route the airflow through the brick lattice so that
fresh air flows first through the recently burned bricks, heating the air, then through the active
burning zone. The air continues through the green brick zone (pre-heating and drying the
bricks), and finally out the chimney, where the rising gases create suction which pulls air
through the system. The reuse of heated air yields savings in fuel cost.
As with the rail process above, the BTK process is continuous. A half dozen labourers working
around the clock can fire approximately 15,000–25,000 bricks a day. Unlike the rail process, in
the BTK process the bricks do not move. Instead, the locations at which the bricks are loaded,
fired, and unloaded gradually rotate through the trench.
24. The Hoffmann Kiln
The Hoffmann kilns were in the form of a
great circular ring chamber, with massive
walls and a large chimney at the centre, to
which underground radial flues converged
from the inside walls of each of the twelve
chambers. The chambers were barrel
arched (like a railway tunnel), and in the
roof arches there were several small feed
holes through which fine coal could be fed
into spaces made among the bricks to be
fired. Around the outer wall or the kiln were
the twelve openings for loading and
unloading the individual firing chambers.
These chambers were separated from
each other by very large metal dampers,
that could be raised and lowered as the fire
moved around the kiln from chamber to
chamber. It is a continuous process.
25.
26. Basic Brickwork Terminology
Stretcher : This brick is laid with its length
parallel to the face front or direction of a wall. The
course containing stretchers is called stretcher
course.
Header : This is a brick laid with its breadth or
width parallel to the face or front or direction of
the wall. The course containing headers is called
header course.
Bed : The lower surface of the brick when laid flat
is known as bed.
Bed Joint : The horizontal layer of mortar upon
which the bricks are laid is known as a bed joint.
Perpends : The vertical joints separating the
bricks in either length are known as perpends.
Lap : The horizontal distance between the vertical
joints in successive course are known as lap.
Closer : A piece of brick which is used
to close up the bond at the end of brick
course is known as closer. It helps in
preventing the joints of successive
courses to come in vertical line. The
types of closer are King, Queen,
Beveled, Mitred closer.
Header
Stretcher
Bed
Joint
Perpend
Lap
Closer
27. Different Forms of Brick
Some of the common type of bricks, depending upon the places of use are listed below :
1. Round End and Bull Nose bricks : are used to construct open drains.
2. Cant bricks : are used for doors and windows they are also called as splay bricks.
3. Double Cant bricks : is used for octagonal pillars.
4. Cornice bricks : is used for architectural point of view.
5. Plinth bricks : used at plinth level construction.
28. 6. Perforated bricks : are well burnt bricks but it is
not sound proof.
7. Hollow bricks : They are 1/3rd weight of the
normal brick and are sound and heat proof.
8. Coping : The top most brick course of parapet is
made with coping bricks. These drain off the
water from the parapet.
9. Queen Closer : when bricks are cut along its
length it is called Queen closer. Its placed near
the quoin header to obtain necessary lap.
10. King Closer : When cut at one end by half
header and half stretcher is known as king closer.
Queen Closer King Closer
Perforated bricks
Hollow bricks
Different Forms of Brick
29. Testing of Brick
(1) Absorption
(2) Crushing strength
(3) Hardness
(4) Presence of soluble salts
(5) Shape and size
(6) Soundness
A brick is generally subjected to the following tests to find for the construction work :
(1) Absorption:
A brick is taken and it is
weighed dry. It is then
immersed in water for a
period of 16 hours. It is
weighed again and the
difference in weight indicates
the amount of water
absorbed by the brick. It
should not in exceed 20 per
cent of weight of dry brick.
(2) Compressive/Crushing strength of
Bricks:
The crushing strength of a brick is found
out by placing it in a compression testing
machine. It is pressed till it breaks. As
per BIS: 1077-1957, the minimum
crushing or compressive strength of
bricks is 3.50 N/mm2. The bricks with
crushing strength of 7 to 14 N/mm2 are
graded as A and those having above 14
N/mm2 are graded. as AA.
30. Testing of Brick
(3) Hardness test on bricks:
In this test, a scratch is made on brick
surface with the help of a finger nail. If no
impression is left on the surface, the brick
is sufficiently hard.
(4) Presence of soluble salts:
The soluble salts, if present in cause
efflorescence on the surface of bricks. For
finding out the presence of soluble salts in
a brick, it is immersed in water for 24
hours. It is then taken out and allowed to
dry in shade. The absence of grey or white
deposits on indicates absence of soluble
salts.
If the white deposits cover about 10 per
cent surface, the efflorescence is said to be
slight and it is considered as moderate,
when the white deposits cover about 50 per
cent of surface. If grey or white deposits
are found on more than 50 per cent of
surface, the efflorescence becomes heavy
and it is treated as serious, when such
deposits are converted into powdery mass.
(5) Shape and size:
In this test, a brick is closely inspected. It should
be of standard size and its shape should be truly
rectangular with sharp edges. For this purpose,
20 bricks of standard size are selected at random
and they are stacked lengthwise, along the width
and along the height.
(6) Soundness test on brick:
In this test, the two bricks are taken and they
are struck with each other. The bricks should
not break and a clear ringing sound should be
produced.
31. Bonds in Brick Work
The manner of overlapping bricks for construction of wall is called brick bond. Many types of
bonds are used in different ways for construction of brick walls or brick pillars. Good brick
bonds can ensure the strength of a building and aesthetic beauty of brick walls, brick pillars
and entire brick works depends on the quality of bonds. For example English bond is widely
used in construction work and is considered to be the strongest bond.
Some rules to be observed for getting a good brick are as
follows:
1. The amount of lap should be min 1/4th brick along its
length and one-half brick along its thickness of the
wall.
2. The brick should be of uniform size to get uniform lap.
3. The use of brick bats and closer for better alignment.
4. The vertical joints in the alternate courses should be
along the same perpend.
32. Stretcher Bond
All bricks are arranged in stretcher course in this bond.
The following are some features of Stretcher bond.
•All bricks laid in stretcher course create stretcher bond.
•This bond is useful for half brick wall/partition walls.
•There is no header in such walls.
•The overlap, which is usually of half brick, is obtained
by commencing each alternate course with a half brick
bat.
Header Bond
All bricks are arranged in header courses. The following
are some features of header bond.
•This brick bond is used for curved surface in brick work
•It is not suitable for load bearing walls because it does
not have strength to transmit pressure.
•The overlap, which is usually-of half the width of the
brick is obtained by introducing a three-quarter bat in
each alternate course at quoins.
•This bond is chiefly used for footings in foundations for
better transverse distribution of load.
33. English Bond
This bond is widely used and is considered
as the strongest bond in brick work. The
following are some features of English
bond.
•Alternate courses/layers consist of stretcher
and header.
•Queen closer is put next to quoin header to
develop face lap.
•In English bond, a heading course should
never start with a queen closer as it is liable
to get displaced in this position.
•Each alternate course/layer of header is
centrally supported over stretcher.
•The number of mortar joints in header
course is nearly double than that made in
stretcher course.
•The bricks in alternate courses have straight
joints.
34. Flemish Bond
In Flemish bond, each course consists of
alternate headers and stretchers. The
alternate headers of each course are
centred over the stretchers in the course
below. Every alternate course starts with a
header at the corner. For the breaking of
vertical joints in the successive courses,
closers are inserted in alternate courses
next to the quoin header. In walls having
their thickness equal to odd number of half
bricks, bats are essentially used to achieve
the bond.
Flemish bonds may be further classified as
(a) Double Flemish Bond
(b) Single Flemish Bond.
35. Single Flemish Bond
This bond is a combination of English bond and Flemish bond. In this work the facing of
the wall consists of Flemish bond and the backing consists of English bond in each
course. This type of bonding cannot be adopted in walls less than one and a half brick in
thickness. This bond is adopted to present the attractive appearance of Flemish bond with
an effort to ensure full strength in the brick work.
1 1/2 brick thk
36. Double Flemish bond
In Double Flemish Bond, each course presents the same appearance both in the front and
back elevations. Every course consists of headers and stretchers laid alternately. This
type of bond is best suited from considerations of economy and appearance. It enables
the one brick wall to have flush and uniform faces on both the sides. This type of
bonding is comparatively weaker than English bond.
1 brick thk
37. English Cross Bond
This is a modification of English bond,
used to improve the appearance of the
wall. This bond combines the
requirements of beauty and strength.
Special features of the bond are as
follows.
•Alternate courses of headers and
stretchers are provided as in English
bond.
•Queen closer is put next to header to
develop face lap.
•A header is introduced next to the quoin
stretcher in every alternate stretcher
course.
• This bond is sufficiently strong and
bears a good elevation.
38. Raking bond:
This is a bond in brick work in which the bonding bricks are laid at any angle other than
zero or ninety degrees. This arrangement helps to increase the longitudinal stability of thick
walls built in English bond. In this arrangement of bonding, the space between the external
stretchers of a wall is filled with bricks inclined to the face of the wall. This bond is
introduced at certain intervals along the height of a wall.
There arc two common forms of raking bond ;
(a) Herring hone bond
(b) Diagonal bond.
(a) Herring-bone bond. This type of bond is best suited for
very thick walls usually not less than four bricks thick. In
this arrangement of brick work, bricks are laid in course
inclined at 45° in two directions from the centre. This bond
is also commonly used for brick paving.
(b) Diagonal bond. This bond is best suited for walls
which are 2 to 4 brick thick. This bond is usually
introduced at every fifth or seventh course along the
height of the wall. In this bond, the bricks are placed
end to end in such a way that extreme corners of the
series remain in contact with the stretchers.
39. Dutch Bond
This is another modification of English bond,
in the bond the corners of the bond are
strengthened. Special features of this bond are
as follows:
•Alternate courses of headers and stretchers are
provided as in English bond.
•Every stretcher course starts at the quoin with
the three quarter bat.
•In every alternate stretcher course, a header is
placed next to the three quarter brick bat
provided at the quoin.
Zig-Zag bond:
This is similar to herring-bone bond with the
only difference that in this case the bricks are
laid in a zig-zag fashion. This is commonly
adopted in brick paved flooring.
40. Masonry Joints
Concave
Flush
Racked
Concave
Struck
Weathered
Vee
Concave Joints Raked Joints
Weathered Joint: Mortar joint has
sloped (downwards) edge
Concave joint: Joint concave inwards
Vee joint: mortar joint is in the form of a
V
Flush Joint: Mortar joint is flush with
the brick surfaces
Raked Joint: A large portion of the
mortar joint is raked out - Not a safe,
impermeable joint
Struck Joint: Mortar joint has a sloped
(upwards) edge
