Water absorption of three different class of bricks are given below : First class- Water absorption of first class bricks after 24 hours of immersion in water should not exceed 20 % of self-weight. Second class- Water absorption of second class bricks after 24 hours of immersion in water should not exceed 22.5 % of self-weight. Third class- Water absorption of third class bricks after 24 hours of immersion in water should not exceed 25 % of self-weight.