Tiles are the last thing a bathroom needs and the first thing owners choose. Fair enough — tiles are the fun part. But three unglamorous decisions underneath them decide whether the room stays dry for fifteen years or leaks into the bedroom by year two.
Decision one: the waterproofing system, in writing
"Contractor will do waterproofing" is not a specification. Ask which system (cementitious slurry and liquid PU are both fine when applied right), how many coats, how high up the walls — full height in the shower zone, at least 300 mm elsewhere — and insist on a flood test before tiling: plug the floor trap, fill to 25 mm, wait 24 hours, check the ceiling below. Any contractor who resists a flood test is telling you something.
Decision two: the falls
Water must reach the floor trap without a detour. A floor with lazy falls puddles at the corner, and standing water finds every weakness in the years that follow. Agree the trap position and the direction of falls before screeding — moving a trap after tiling is demolition, not adjustment.
Decision three: the pipe routes
Every pipe buried in a wall should be pressure-tested before it is plastered over, and photographed with a measuring tape in frame. That photo is your map for the next twenty years — every future renovation, towel-rail installation and picture hook depends on knowing where the pipes run. We give clients a wall-by-wall photo set as standard.
The order of operations
Plumbing first fix → pressure test → screed and falls → waterproofing → flood test → then, and only then, tiles. If a schedule compresses the middle steps to save days, the bathroom will collect that debt with interest.