Bathroom Waterproofing: What Should Be Done Before Tiling?

Bathroom leaks are the most common complaint in Indian homes after handover and the most expensive to fix, because the fix means breaking tiles. Almost all of them are prevented by doing five things in the right order before the first tile is laid.

The sequence

1. Prepare the sunken slab. Most bathrooms use a sunken slab (300–450 mm deep) to conceal drainage. Repair honeycombing, cove the slab–wall junction with a 45° mortar fillet, and cure.
2. Complete and test plumbing. All drainage and supply lines fixed, with floor traps set to final level. Pressure-test supply lines; check drainage falls. Nothing gets waterproofed with a pipe still to be moved.
3. Apply the waterproofing. Two coats of a cementitious polymer coating (or a liquid membrane) over the slab, up all walls to at least 300 mm above the finished floor — and to full height at the shower wall. Collars around every pipe penetration.
4. Ponding test. Flood the sunken portion to 50 mm for 48–72 hours; inspect the ceiling below. Fix and re-test before proceeding.
5. Fill and screed with slope. Fill the sunken portion with lightweight material (not loose rubble), lay a screed with a slope of about 1 in 60–80 to the floor trap, then tile on a suitable adhesive with grout sealed.

Shortcuts to refuse

• Waterproofing applied only on the floor, with no upturn on the walls.
• Filling the sunken slab with loose brickbats and site debris — it holds water and loads the slab.
• Tiling without a ponding test "to save a week".
• Grout left unsealed; it is the first path for water once the coating is under tiles.
• Skipping the coving, so the coating cracks at the sharp corner.