The most common failures are: setting the drain level to the screed instead of the finished tile, stopping waterproofing at the drain edge, reducing the floor slope to make the drain fit, fixing the drain directly to a timber floor, and damaging the finish during tiling.
1. Wrong level reference
The drain is set level with the screed, but the tile is installed on top. Result: the grate sits below the tile surface (water pools around it) or, if over-corrected, stands proud as a trip hazard. Always level to the finished tile line.
2. Waterproofing stops at the drain
The membrane is cut around the drain body instead of being bonded over the flange. Water reaches the membrane and tracks sideways under the drain. Every drain must have a continuous, bonded membrane connection.
3. Slope reduced to fit the drain
When the drain is deeper than the available build-up, the installer reduces the fall instead of changing the drain. Water then pools at the far end of the shower. Change the drain, not the slope.
4. Drain fixed directly to timber
Floorboards deflect. The drain moves, the tile cracks and the waterproofing seal breaks. A rigid support frame between joists is required — see wooden subfloors.
5. Finish damaged during tiling
Stainless steel scratches and holds mortar residue. Grate left unprotected during tiling is often damaged, then cleaned aggressively with abrasive products, making it worse. Leave protective film on until handover.
6. Inaccessible hair trap
The drain is installed without checking how it will be cleaned. Debris accumulates and the drain blocks. Confirm the grate lifts out and the trap is reachable before tile is fixed.
7. Insufficient outlet fall or too many bends
The drain itself is fine but drains slowly because the waste pipe has insufficient fall or unnecessary bends. Check the outlet route before installation.
8. No water test
Testing after tiling means a leak can only be found by removing the floor. Water test at membrane stage, before screed and tile.
Related: installation sequence · slope requirements