Tiles Are Not Waterproof
This surprises people, and it is the root of nearly every shower leak we attend.
Ceramic tiles are impervious, but the grout between them is not, and neither is the substrate behind. Water passes through grout lines continuously in normal use. In a shower, that means the wall and floor behind the tiles get wet every single day.
What stops that water reaching the timber, the wall cavity or the flat below is a waterproof membrane applied to the substrate before the tiles go on. The tiles are the wearing surface and the finish. The membrane is the waterproofing.
So when a shower leaks, re-grouting and re-sealing addresses the visible joint and leaves the actual problem untouched. It buys a few months. Sometimes it buys less.
Done Before Tiling, or Done Twice
The unavoidable arithmetic of shower waterproofing is that doing it correctly costs a fraction of doing it late.
At first fix, before tiling, the membrane goes onto a prepared substrate, the falls are formed to the waste, the corners and junctions are reinforced, and the whole thing is tested. It is quick and it is comparatively cheap.
After the fact, on a leaking shower, the tiles come off, the substrate is usually water-damaged and has to be replaced, sometimes the timber below has gone, and everything is reinstated. It is a different order of job.
What proper installation involves:
Substrate. Sound, dry and appropriate. Standard plasterboard in a wet area is a problem waiting to happen. Cement backer board or a suitable tile backer is the right material.
Falls. The floor must fall to the waste from every direction. A shower floor that ponds pushes water at the perimeter continuously.
Bond breakers and reinforcement at every junction. Wall to floor, corner to corner, and around the waste. These are the points that move, and a membrane that is rigidly bonded across a moving junction splits along it.
Upstand height. The membrane carried high enough up the walls, and beyond the shower area where required.
The waste and any penetrations detailed into the membrane, not just up to them.
Flood test before tiling. The one step that gets skipped most often, and the only way to know before tiling that the membrane actually works.
Where Shower Leaks Show Up
In the room next door. A wet patch on the other side of the shower wall, often at skirting level, is a classic shower membrane failure.
In the ceiling below. On an upper floor or in a flat, this is where it goes, and in a sectional title block it becomes somebody else ceiling.
At the door frame or hob. Where the shower meets the rest of the bathroom, if the upstand or the threshold detail is short.
Nowhere visible, for years. Water quietly wetting timber inside a wall or floor, until the floor becomes soft or the smell appears. This is the expensive version.
Mould and black spot around the shower, which in Cape Town needs distinguishing from ordinary condensation. Most Cape Town bathrooms are poorly ventilated and mould around a shower is often just that, not a membrane failure. We check rather than assume, because the two have very different price tags.
