According to Indian standard(IS: 1077: 1992) bricks are classified into the following categories:
Classes of common burnt clay bricks:
Class Designation Average compressive strength not less than[ (N/mm^2) (kg/cm2)
- 35 35 350
- 30 30 300
- 25 25 250
- 20 20 200
- 17.5 17.5 175
- 15 15 150
- 12.5 12.5 125
- 10 10 100
- 7.5 7.5 75
- 5 5 50
- 3.5 3.5 35
- Bricks shall be hand moulded or machine moulded and shall be made from suitable soils. They shall be from from cracks and flaws and nodules of free lime.
- Bricks with height of 90 mm or 70 mm will be moulded with a frog of 10 mm to 20 mm deep on one of its flat sides. Bricks with height of 40 mm or less, and as well those made by extrusion process may not be provided with frogs.
- The bricks shall have smooth rectangular faces with sharp corners and shall be uniform in colour
.For other detailed dimensions and tolerance criteria please visit the IS 1072 : 1992
In some books the classification of the bricks is given as below:
(1) First Class Bricks
(2) Second Class Bricks
(3) Third Class Bricks
First class bricks:
(1) Plain surface, sharp edges and size with tolerance in dimensions +-3%
(2) Uniform red or brownish colored.
(3) High crushing strength, not less than 10.7 N/mm2
(4) Machine moulded
(5) Efflorescence- NIL
(6) Water absorption less than 15%.
USE: They are used for the exterior wall brick works, short columns and arches.
Second class bricks:
(1) Slightly uneven faces and edges with tolerance in dimensions +-8%
(2) Uniform colored but may be slightly over burnt.
(3) High crushing strength, not less than 7 N/mm2
(4) Hand moulded
(5) Efflorescence- Little
(6) Water absorption less than 20%.
USE: They are used for internal walls and compound walls.
Third class bricks:
(1) May be distorted with blunt edges.
(2) Over burnt or under burnt and non uniform color.
(3) High crushing strength, not less than 3.5N/mm2
(4) Hand moulded
(5) Efflorescence- Large
(6) Water absorption less than 25%.
USES: They are used for flooring, paving, small brick foundations and brick bat lime concrete(B.B.L.C.).
References: 'Engineering Materials' by S C Rangwala