A bathroom leak almost never shows up where the actual defect is — it travels through the slab and shows up as a damp patch on the ceiling below, sometimes many months later. That is why the sunken portion, the pipe sleeves and the wall-floor junction need to be treated with as much care as any structural element, not rushed through in a day just to keep the tiling gang moving.
The sunken slab must be given a proper slope, typically about 1 in 100, towards the floor trap so that water does not pond in corners. Whether you use an integral waterproofing compound in the concrete, a crystalline coating, or a membrane system, the golden rule is the same: take it up the walls by at least 300 mm so that splash water and standing water at the wall base cannot seep sideways into the wall. Pipe penetrations for the floor trap, water closet outlet and other sleeves are the weakest points, so factory-made pipe-seal collars or properly done PU sealant collars around every pipe are non-negotiable.
Before you let the tiler in, insist on a pond test — fill the sunken area with water and let it stand for 48 to 72 hours, checking the slab below for any seepage. Only after this test passes should tiling proceed, using proper tile adhesive and, in wet areas, epoxy grout instead of ordinary cement grout because epoxy resists water and staining far better over the life of the bathroom.
Wall upturn
300 mm
Pond test duration
48-72 h
Floor slope to drain
1:100
Remember on site
- Slope sunken slab about 1:100 to the floor trap and take waterproofing 300 mm up the walls
- Seal every pipe penetration with a collar; these are the most common leak points
- Do a 48-72 hour pond test before tiling, and use epoxy grout in wet areas
Check yourself
What is the typical slope given to a sunken bathroom slab towards the floor trap?
How high should waterproofing treatment be taken up the bathroom walls?
Why are pipe-seal collars used around sleeves passing through the sunken slab?
How long should a pond test be maintained before allowing tiling to start?
Which grout type is preferred in wet areas like bathroom floors and shower walls?
What does an integral waterproofing compound do?
Crystalline waterproofing works mainly by which mechanism?
Where should the pond test water level typically reach?
Why must waterproofing be checked before tiling and not after?
Which of these is NOT a common waterproofing system used for wet area slabs?
At the junction of the sunken slab and the wall, what detail matters most?
What gap is typically kept between tiles using spacers, apart from waterproofing considerations?