How long should bathroom waterproofing last?

A waterproof membrane is not a consumable. Installed to the standard, on a properly prepared substrate, with the right detailing at junctions and penetrations, it should outlast the tiles above it. When one fails at five or eight years, the cause is almost always something that happened during installation.

Common causes of early failure

• Insufficient coats, or a membrane applied thinner than the manufacturer specifies.
• Poor substrate preparation, dust, moisture or an unsuitable board behind it.
• Junctions and penetrations not detailed properly. Corners, floor wastes and tap penetrations are where membranes actually fail, not in the middle of a flat wall.
• Inadequate falls to the floor waste, leaving water sitting rather than draining.
• Tiling started before the membrane had properly cured.

This may be a defect, not a repair

Residential building work in Australia carries statutory warranties, and the period is measured in years rather than months. If a bathroom was waterproofed as part of licensed building work and has failed early, that is potentially a defect claim against the builder rather than a job you simply pay to redo. The periods, the process and the dispute body all differ by state.