Brick is a regular sized rectangular unit, used for most of the building works. Bricks are obtained by moulding plastic mass of suitably proportioned earth in timber or steel moulds. Moulded bricks are first allowed to dry and then burnt in kilns designed for the purpose. Bricks are always rectangular in shape and of such proportion that the length is generally twice the width plus the thickness of mortar joint. Thickness of the brick is less than or at the most equal to the width of the brick. The size of the brick is such that it can be easily lifted and handled with one hand. They do not require any lifting appliances. It is used as substitute for stone, where stone is not available. Comparison of stone with brick as a material of construction is given in Table 1.1.
In general, bricks may be classified into following five categories :
(i) First class bricks
(ii) Second class bricks
(iii) Third class bricks
(iv) Over burnt or Jhama bricks
(v) Under burnt or pilla bricks
First Class Bricks
The earth from which bricks have been made should be suitably proportioned. It should be free from small pebbles, lime lumps, organic, matter, and sodium salts.
A first class bricks should possess the following properties :
(i) Size of the burnt brick should be exactly 19 × 9 × 9cm.
(ii) It should be well burnt
(iii) Its colour should be uniform yellow or red.
(iv) It should not absorb water more than 20% of its own dry weight after 24 hours of immersion.
(v) It should have a firm, compact, and uniform texture.
(vi) Its surface should be regular and sides parallel. Edges should be sharp and at right angles to each other.
(vii) Its fractured surface should not show fissures and bubbles or lumps of lime.
(viii) Its crushing strength should not be less than 105 kg/cm2.
(ix) Two first class bricks when struck with each other give a sharp metallic ringing sound.
(x) It should not show any signs of efflorescence when bricks are dried after soaking in water.
(xi) The brick should not break when it is dropped on a hard ground from a height.
(xii) Its surface should be so hard that finger nails should not be able to make any impression on its surface.
Second Class Bricks
Brick of this category should possess the following properties :
(i) The brick of this class should also be well burnt. They can even slightly be over burnt.
(ii) Minimum crushing strength should be 70 kg/cm2.
(iii) They should not absorb water more than 22% of its own dry weight after 24 hours of immersion in cold water.
(iv) Two second class bricks when struck with each other give a metallic ringing sound.
(v) These bricks should not show appreciable signs of efflorescence when soaked bricks are dried.
(vi) The shape, size and colour of the brick should be generally regular and uniform. Slight distortion and surface cracks may however be allowed.
(vii) Texture of these bricks should be uniform. Presence of small pebbles may however be allowed. Presence of limestone and kanker should not be allowed to occur.
Third Class Bricks
A third class brick should possess the following properties :
(i) These bricks are generally under burnt.
(ii) They are soft and light coloured.
(iii) They may suffer from intensive efflorescence.
(iv) They emit a dull sound when struck against each other.
(v) It should not absorb water more than 25% of its own dry weight when kept immersed in water for 24 hours.
(vi) Texture of above brick is not uniform and it may show lot of pebbles on freshly fractured surface of the brick.
(vii) Size and shape of these bricks is not regular. But the irregularities should not be so much that it may become difficult to have the course of uniform thickness, in masonry work.
Uses of Bricks
(i) First class bricks are used for following purposes :
(a) It is used for all sound work of a permanent character.
(b) It is used in the face work of structures not to be plastered but only pointed.
(c) It is used in flooring and reinforced brickwork.
(ii) Second class bricks are used for the following purposes :
(a) It is used in unimportant situations or at places where the masonry is to be plastered.
(b) Used as brick ballast in R.C.C. work and in Lime concrete.
(iii) Third class bricks are used for the following purposes :
(a) These bricks are not used for important and permanent works.
(b) These bricks are used in temporary constructions not subjected to heavy loads or heavy rains.
Brick Sizes
According to I.S.I., the size of the brick without the thickness of mortar joint is 19 cm × 9 cm × 9 cm. The size with mortar joint becomes 20 cm × 10 cm × 10 cm. Hence, the effective size of brick is taken as 20 cm × 10 cm × 10 cm. If thinner bricks are required, their standard size is 19 cm × 9 cm × 4 cm and effective size is 20 cm × 10 cm × 5 cm. The minimum compressive strength of the standard bricks should be 35 kg/cm2.
