Slab which is provided below the washrooms to hide the sewage pipes or sewerage pipes is called Sunken slab. Since the pipes that carry water are concealed below the floor, care has to be taken to avoid leakage problems.  After casting sewage pipes in the slab the slab is filled with coal or broken pieces of bricks. There are two types of sunken slab.

1. The slab which is provided below the normal floor level at a depth of 200mm to 300 mm and filled with broken pieces of bricks is called Sunken slab

2. The Slab which is provided above the normal floor level at a height of 200mm to 300mm and filled with coal or broken pieces of bricks called sunken slab.