How to Waterproof Your Bathroom: Step by Step

Bathroom waterproofing should be done during construction or renovation — before tiles go up. It's applied on the concrete/screed surface, then tiles are laid on top. Retrofitting waterproofing on an existing tiled bathroom is much harder and less effective (though injected sealants exist for emergency fixes). If you're renovating your bathroom, this is your one chance to get waterproofing right.

The surface must be clean, dry, and free of loose material. Hack off old tiles and adhesive. Fill all cracks and holes with polymer-modified mortar. Create a 'cove' (curved fillet) at the wall-floor junction — this prevents water from seeping into the corner joint. Ensure the floor slopes towards the drain outlet (minimum 1:60 gradient). Cure any fresh mortar for at least 24 hours.

Use a cementitious waterproofing system like Dr. Fixit Newcoat or Sika TopSeal 107. Mix the two components (liquid + powder) as per instructions. Apply the first coat with a brush — cover the entire floor and up the walls to at least 1 foot above the finished floor level. In the shower area, go up to 6 feet or full height. Allow 6-8 hours drying. Apply the second coat perpendicular to the first. Allow 24 hours curing.

Pay extra attention to: wall-floor junctions (use reinforcement tape embedded in the waterproofing), pipe penetrations (apply extra coats around pipes), drain outlet junction, and the door threshold. These are where 90% of bathroom leaks originate. Apply an additional coat at each of these points.

Before tiling, do a ponding test. Block the drain outlet, fill the bathroom floor with 2-3 inches of water, and leave it for 24-48 hours. Check the ceiling below for any damp spots. If the test fails, apply additional waterproofing coats and retest. This test is critical — much easier to fix now than after tiling. Once passed, proceed with tiling using polymer-modified tile adhesive.