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Hi, I'm after some advice on prepping new walls before tiling.

After reading numerous posts on the subject I was hoping for some advice on my specific set up.

We're having a bath with a mixer shower over the top, with two walls tiled from the bath to the ceiling then the 3rd being a shower screen. Everything will be ripped back to the studs and replaced.

My plan was to plasterboard the whole area and use a liquid tanking system (mapei) on the areas that will be getting wet constantly including a niche that will be built in. Then apply a cement based adhesive before tiling.

I've looked at using cement based boards behind the wet areas and not bothering with tanking as I'm not convinced with how much water will actually get thru and if any were to it would evaporate before any damage occurs.

Any opinions/advice would be appreciated.

Many thanks

We always put aquapanel (or similar other brands) behind showers, but I don't see any problem with tanked plasterboard as an alternative. As long as you do one or t'other -- once you've seen a few damaged baths/showers as result of tiles falling off sodden plasterboard, and leaks through downstairs ceilings caused by the same, you know it's worth doing!

Personally I'd go with the cement board every time in the situation you have. even the slightest weep from a joint somewhere behind plasterboard will destroy it over time... whereas cement board will withstand it.

(Not that my plumbing ever has any weeps... OK except that one )

Would you say that tanking is overkill then for my situation and that cement board would be suffice?

Yep. If you're fitting cement board then it doesn't need tanking. However, the edges of the boards should be sealed and taped before tiling over.

Sealed with say a bead of silicone and taped using skrim tape?

Chrispy61 wrote:Sealed with say a bead of silicone and taped using skrim tape?

Follow the manufacturer's guidelines for whatever product you use, but basically, yes. Knauf sell their own jointing adhesive for aquapanel. It's basically very overpriced silicone as far as I can tell. You run it along the edges of the board before you butt them up against each other, and remove whatever squidges out from the surface. I'm sure Knauf will say their product has been specially formulated and contains secret magical properties that other silicones don't have, blah... blah... blah. 'sup to you whether you buy into that or not!

Cheers for the advice.

Would it be the same sort of thing with the niche? Cement board to make the box before the tiles go in? With all the joints butted and sealed with sealant?

Yep, exactly the same with the niche. When you're tiling the bottom "shelf" of the niche, the tiles should be raised slightly at the back to allow water to run off rather than collecting in there. I suppose you could build that angle into the framework of the niche itself, but in my experience (I fit bathrooms, but I'm not a tiler myself), the tiler will do that by building up the tile adhesive a few mm at the back.

That's brilliant, cheers mate. Is this how you would normally do your bathroom fits?

From your experience, how often when you rip out a bathroom, do you find damage from water getting thru into the substrate behind the tiles?

Not so much when just doing a bathroom refit (but I don't actually do that many - maybe 5 or 6 a year), but I do a fair bit of "emergency" plumbing work and I've seen several of instances where big sections of tiles have come crashing down into a bath or shower tray. All it takes is for a tiny bit of tile grout to fall out and be ignored for a few weeks or months. The water soaks into the paper behind the tiles and spreads behind them through capillary action. Then, eventually, BOOM! - big section of tiling falls off the wall, including the tile adhesive, and the mouldy paper from the front of the plasterboard. There's no cheap way to fix it either -- bath or shower tray out, any remaining tiles off the wall, rip the plasterboard out and replace with cement board.

I've seen other people on the internet saying it's fine to use plasterboard as long as you use waterproof adhesive and grout. Put it this way -- having seen the damage it can cause, I wouldn't do that in my house. It may be fine for 3 or 4 years until the sealant needs redoing or a tiny segment of grout comes out...

From what I can gather, most adhesive's and grout's aren't fully waterproof but only water resistant. But if you were ever to get a crack in the grout I wouldn't imagine water being able to pour thru adhesive then cement board but for it to be absorbed then evaporate with no damage done.

Thanks again for your help

As a alternative, marmox boards are fully waterproof, have thermal and sound reducing benefits.

Could be another good option, would be belt and braces aswell? What's your opinion?

I've used a few different brands of tile backer boards, but I honestly don't know if Marmox is one of them as it's not normally me who buys it. I'm sure any brand of cement-based board would be fine though -- whatever's cheapest, or in stock at the suppliers. The main problem with plasterboard is just that it's held together by paper and disintegrates when damp, as anyone who's ever tried to pick one up that's got a bit damp outside will know!