How to waterproof a bathroom before tiling (wet-area guide)

The floor and wet walls must be sound, clean and to the right falls toward the drain. Fill big gaps, round off internal corners, and dampen absorbent surfaces so they do not pull water from the coating.

Bed reinforcing tape into a first pass of coating at all floor-to-wall corners, wall-to-wall junctions, pipe penetrations and around the drain. These movement points are where waterproofing most often fails.

Brush/roller a full, even first coat of SUMO Sealcrete or Flexguard over the whole wet area, up the walls to the required height (higher in showers). Work it into the surface with no misses.

Once the first coat has cured enough to over-coat, apply the second coat at right angles to the first for full, pinhole-free coverage. Two crossed coats give an unbroken film.

Let the membrane cure fully, then plug the drain and flood-test the floor to confirm it holds before you tile. Fix any leak now, not after tiling.

Fix tiles onto the cured waterproofing with a polymer-modified C2 adhesive such as SUMO S02+ or S03, then grout — ideally with epoxy grout in the shower zone.