Tank the wall first, then tile. Waterproofing goes on behind the tiles, never over them — because tiles and grout aren't waterproof, and the tanking layer underneath is what actually stops water reaching the wall. Get that one thing right and a shower lasts decades. Get it wrong and you'll be ripping it out, no matter how neat the tiling looks.
I've pulled out plenty of showers that failed, and it's almost never the tiling that let go. It's that nobody tanked it, or they tanked the flat wall and ignored the corners. This is how to do it properly.
Key Takeaways
- Tank before you tile. The waterproof layer goes on the wall first, under the tiles.
- Leaks start at the details — corners, the wall-to-tray joint, and pipe penetrations — not the open wall.
- Don't tile straight onto plasterboard. Use a cement or waterproof backer board, then tank it.
- Silicone, not grout, goes in every joint that moves (wall-to-tray, internal corners).
- Let the tanking cure before you tile. It's a day-one job, not a last-minute one.
Why tanking matters (and why grout won't save you)
People assume tiles waterproof a wall. They don't. Grout is porous, and over months and years water works through the grout joints. In a splashed-once-a-day kitchen that's no drama. In a shower that gets soaked every single day, that water has to be stopped somewhere — and that somewhere is the tanking: a waterproof membrane applied to the wall before the tiles go on.
No tanking, and the water reaches the substrate. If that substrate is plasterboard, it swells, goes soft, and the tiles eventually let go — usually after the silicone's also failed and water's been tracking behind for months. By the time you see it, the damage is done.
Where showers actually leak
This is the bit experience teaches you: showers don't leak in the middle of the wall. They leak at the details.
- Internal corners — where two walls meet, and where the wall meets the tray or bath. Constant movement and constant water.
- Pipe and valve penetrations — anywhere a pipe or the shower valve comes through the wall.
- The wall-to-tray joint — the most-soaked joint in the whole room.
That's why every tanking system makes such a fuss about reinforcing tape and extra membrane at corners and penetrations. The flat wall is the easy bit. The corners are where the job is won or lost.
Step 1: Get the substrate right
Don't tile a shower straight onto standard plasterboard. Even moisture-resistant (green) board isn't a waterproof base on its own.
For a shower I want a cement-based backer board or a waterproof tile backer board fixed to the studs or battens. It's a stable, water-tolerant base that tanking and adhesive both grip well. If you're working over an existing moisture-resistant board you can't remove, it must be tanked — but if you're building it up fresh, fit a proper backer board. It's a couple of hours that saves you the whole job.
Whatever the substrate, it needs to be flat, sound, and fixed solid — the same principles as any tiling base, covered in subfloor prep before tiling (the wall version of the same rules).
Step 2: Prime, then tank
Most tanking systems want a primer first — it controls how porous the board is so the membrane bonds and cures right. Don't skip it if the instructions call for it.
Then tank. For a standard domestic shower, a liquid tanking kit does the job: a paint-on waterproof membrane plus reinforcing tape that gets bedded into the membrane at every corner, joint, and penetration.
The order that matters:
- Treat the details first — bed the reinforcing tape into a coat of membrane at internal corners, the wall-to-tray joint, and around every pipe.
- Coat the flat areas — apply the membrane across the whole wall, working it well into the surface.
- Second coat — once the first is touch-dry, a second coat at right angles to the first for full, even coverage.
- Let it cure. This is the wait people skip. Tiling over half-cured tanking traps moisture and undermines the whole point.
Tanking kit vs matting: a sheet tanking membrane (matting) bonded to the wall is tougher and lets you tile straight away with no drying wait — worth it on a wet room or a job you want belt-and-braces. For most domestic showers a quality liquid kit, done patiently at the corners, is plenty. Both work. A rushed install of either doesn't.
Step 3: Set out and tile
With the tanking cured, tile as you would any wall — but plan the set-out around the shower. The full method (datum line, batten support, adhesive, cutting, grouting) is in how to tile a wall. The shower-specific points:
- Work from a level datum, not the tray. Trays aren't always dead level.
- Plan your cuts so you don't end up with a thin sliver of tile in the most visible corner.
- Use the right adhesive — a wet area wants a suitable cementitious adhesive, not a tub of ready-mixed wall-tile paste. The adhesive buying guide covers which class to use where; ready-mixed pastes are not for showers.
- Keep your tile movement minimal over penetrations — cut neatly around the valve, don't force tiles tight against pipes.
Step 4: Grout — then silicone the movement joints
Grout once the adhesive's fully cured. For a shower, choose your grout for a wet environment — sanded or unsanded by joint width, and epoxy if you want maximum water and stain resistance. How to choose tile grout walks through it. You'll get a fine haze on the tile face after grouting; grout haze removal covers clearing it.
Then the part people get wrong: the moving joints get silicone, not grout. The wall-to-tray joint, the internal corners, and around the valve all flex slightly. Grout in a flexing joint cracks — every time — and a cracked joint is an open door for water. Use a quality sanitary silicone (mould-resistant) and tool it neatly.
The honest bit on standards
Waterproofing wet areas properly is best practice for a reason — warranties and good building practice both expect a shower to be tanked, and a failed shower can mean damage to the room below, not just the tiles. I'm not going to quote you chapter and verse of a regulation I'd have to look up; the practical standard is simple and hasn't changed in my fifteen years on the tools: if it gets soaked daily, it gets a proper waterproof layer behind the tile. Do that and you're on the right side of any standard that matters.
Where this fits in the bigger job
Tanking the shower is one stage of the full bathroom. For the whole job in order — plan, prep, tank, walls, floor, grout, seal — see the complete bathroom tiling guide.
Related guides
- How to tile a wall — the full wall-tiling method
- Subfloor prep before tiling — getting the base right
- Tile adhesive buying guide — which adhesive for a wet area
- How to choose tile grout — grout for wet rooms
- The complete bathroom tiling guide — the full job in order