When a shower leaks within 6-24 months of a re-tile, the cause is almost always waterproofing membrane failure rather than a tile or grout problem. Australian Standard AS 3740 specifies how wet-area waterproofing must be installed, but real-world compliance is patchy — and the consequences only show up months later when the membrane fails under pressure.
Why grout is rarely the actual leak
Cement-based grout is not waterproof and never has been. AS 3740 treats grout as decorative and moisture-tolerant, not as a barrier. The waterproofing membrane underneath the tiles is the actual barrier — and if it has failed, no amount of regrouting fixes the leak. Regrouting a leaking shower is a temporary cosmetic fix, not a repair.
Six common waterproofing failures
1. Membrane not turned up the wall to required height
AS 3740 requires the waterproofing membrane to extend at least 100mm above the finished floor inside the shower enclosure (and higher in some configurations). If the membrane stops at floor level, water that gets behind tiles tracks under the wall.
2. No membrane at the hob junction
The shower hob (the lip at the entrance) is the highest-risk failure point. Water sits there longest, expansion-contraction cycles are highest, and many tilers skip the bond-breaker tape that AS 3740 requires at this junction.
3. Membrane punctured by tile fixings
Some installers fix tile-to-substrate after the membrane is applied without realising the fixings have punctured it. Each puncture is a leak point. The fix is a substrate-fix-then-membrane sequence, never the other way around.
4. No bond-breaker tape at junctions
Wall-to-floor junctions and around penetrations need bond-breaker tape so the membrane can flex with substrate movement. Without it, the membrane cracks at junction lines as the building moves and water finds the crack.
5. Insufficient membrane thickness
Liquid membranes need two coats minimum, with the first fully cured before the second. Thin single-coat application is a common shortcut and the membrane fails inside 12 months.
6. No membrane installed at all
On older homes (pre-2000s), original showers often have no waterproof membrane underneath the tiles — the tiles and grout were the waterproofing. A re-tile that does not strip back to the substrate and apply a membrane is just covering up the original failure.
How to verify a real waterproofer
- Ask for a current waterproofing certificate (separate from a tiling Cert III)
- Ask for photos of the membrane application from previous jobs
- Confirm two coats of liquid membrane (not just one) in the quote
- Confirm bond-breaker tape application is included
- Ask for a 10-year workmanship warranty in writing
- Walk away if the quote is "too good to be true" — proper waterproofing is labour-intensive