Characteristics of Second Class Bricks
Second class bricks are somewhat less superior than first-class bricks. Following are the 9 characteristics of a second class brick:
1. Second-class bricks are burnt in kilns.
2. They are ground-moulded.
3. The crushing strength of a second class brick should not be less than 7 N/mm2.
4. They are rectangular in shape, but their edges are not accurately uniform and sharp as like first-class bricks.
5. They are free from cracks but small cracks and distortions are permitted.
6. Dry second-class bricks should not absorb water more than 22% of their own weight when immersed in water for 24 hours.
7. They emit a ringing sound when two bricks are struck each other.
8. They are light red in colour, but the colour of the brick is not the same throughout the area.
9. The surface of these bricks is somewhat rough.
Second class bricks are preferable for all important and as well as unimportant masonry work.
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Characteristics of First Class Bricks