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Grout is not waterproof
Cement based grout is porous. Over time water soaks through it, and if there is nothing behind the tiles to stop it, the moisture reaches plasterboard or plaster. Standard plasterboard softens when wet, tiles loosen, and water tracks down to the floor void.
Worn silicone around a tray or bath is the other classic route. Once the seal splits, every shower pushes water into the gap between the tray and the wall.
- Porous grout letting water through to the board
- Split or mouldy silicone along trays and baths
- Ordinary plasterboard used in a wet area
- Trays laid without enough support or fall
- Leaking joints on waste or supply pipes
What tanking does
Tanking is a waterproof membrane or coating applied to walls and floors in wet areas before tiling. Corners and pipe entries are reinforced with tapes and seals, because those are the points where movement opens cracks. With tanking in place, any water that gets through the grout stops at the membrane instead of reaching the structure.
We tank wet areas as standard on our bathrooms. It is one of the parts of a bathroom you cannot see, and one of the parts that matters most.
Using the correct backer board
Behind the tanking, the wall needs a board designed for wet rooms. Cement or foam based backer boards do not break down when damp and give tile adhesive a stable surface. Boarding with the correct backer is part of how we build every shower enclosure and wet room.
Shower tray replacement
- Cracked and loose trays replaced, not patched
- New tray set to accurate falls on a solid base
- Surrounding tiles and sealing made good
Getting the falls right
Water must run to the waste, not sit in a corner. On a shower tray that means the tray is bedded fully and level so it does not flex. On a wet room or walk in floor, the former has to be set with accurate falls towards the drain so water never pools against the walls.
A tray that rocks slightly underfoot will eventually crack its silicone seal, however good the product. Solid support is part of the waterproofing, not an afterthought.
Testing before anything is closed up
Once pipework is in, we pressure test before walls are boarded and tiled. A weeping joint found at this stage takes minutes to fix. Found after tiling, it can mean taking a finished wall apart.
Final sealing then goes on as the very last job, once tiling and grouting are complete.
If your shower is already leaking
Resealing can buy time where the only fault is tired silicone, but if tiles are loose, grout is crumbling or the board behind is soft, the water has already reached the wall. The lasting fix is to strip back to the brickwork and rebuild the area with tanking, the correct backer and a properly supported tray.
Read more: shower leaking through the ceiling, shower tray replacement
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Common questions
- Can I just regrout to stop a leak?
- Only if the board and tiles behind are still sound. Grout is porous, so it is never the waterproof layer on its own.
- Do you tank every shower?
- Yes. We tank wet areas and board with the correct backer as standard on our bathroom work.
- Is a wet room more likely to leak?
- Not when it is built properly. The whole floor is tanked and the former is set with accurate falls to the drain.
- Why do you pressure test the pipes?
- So any weak joint is found and fixed before walls are closed up and tiled.
- Can I keep using another toilet while you fix the bathroom?
- We keep one working toilet in the house wherever the layout allows.
The service behind this guide
Covering Hertfordshire and Essex.