Block wall wetroom

22 Nov 2006
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United Kingdom
Advice appreciated as always. I am installing a wetroom. The area in the shower area is 90cm x 1m. Two walls are stud, one wall is bare block work which runs the length of the shower room. I was planning to use cement boards on the stud walls and then tank the shower area when all fitted. What would be my best options please for finishing the bare block wall - plaster? wedi boards?, something else before the area is tanked

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Instead of using cement boards use construction boards like marmox, wedi, jackoboard, STS or similar. The advantage of these is they are completely waterproof and don't require tanking, just tape the joints and screw heads. Use the opportunity now to level up and strengthen your stud wall and think ahead about any fittings which will be on this wall as you can fit studwork/plywood/OSB to provide solid fixing points. For your block wall first prime using an acrylic primer or SBR and fix the construction boards with cement based tile adhesive. Follow the manufacturers instructions but usually each 1200x600 board will require 5 blobs of adhesive to dot and dab to the wall. Mechanically fix through the adhesive once fully cured using the correct washers. Use the correct tape to waterproof the joints and cut pieces of the tape off to cover all screw heads. Prime again and you're ready for tiling. Here's a couple of pictures of a recent one I did using Marmox boards to give you an idea of how it might look. Left hand wall is block and right hand wall is studwork. Good luck.


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That wet room former was the Impey Aqua Dec easyfit along with the Waterguard tanking kit. In my opinion they are one of the best out there. The former is 22mm thick, has an adjustable waste to avoid joists, they don't require any form of underboarding and will take up to about 300kg. With wet rooms I also replace the surrounding floor with 22mm No More Ply so the transition between floor and tray is solid and seamless.


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You've done a great job Jaimie. I have screed an Impey aquagrade in place (900 x 900mm). Like you suggest I will look at using construction boards and then the Impey Waterguard tanking kit. Which toilet frame/toilet did you use?.

I have another wetroom I am fitting upstairs (ensuite) and was actually looking at the Impey aquadec. The ensuite is 3.66m x 1.50m . The size of the area I was planning for the shower area is 1.50m x 1.20m and I see Impey do an aquadec that size. I currently have 18mm ply flooring. Would you suggest fitting the aquadec and then remove all the exisiting 18mm ply in the whole room and replace for 22mm no more ply? and again using construction boards all round shower area on the walls. The area above the double basin (outside the wetroom, beyond a planned glass screen) I was planning not to tile - would I use moisture resistant plaster board on these areas (outside the showering area)

Thanks for all you help.
I honestly can't remember which toilet frame was used on that, I'll see if I can find out. Upstairs I would replace all the surrounding floor with the 22mm No More Ply, it's tongue and grooved and rock solid when fixed. For a wet room it's definitely the best option as it's the same thickness as the Impey former, it's unaffected by moisture and will not rot. As for the walls outside the showering area, moisture resistant plasterboard would be fine, especially if your tiles are of a larger format with less grout lines. If you are planning mosaics or smaller tiles with more grout lines then I'd suggest continuing around with construction boards as they are fully waterproof. Good luck with both bathrooms.
Minimum thickness for solid walls is 12.5mm carlsbergy. It is for Marmox anyway, which tends to be the one I use most often, but check with whichever one you choose.
What screws would you suggest Jaimie for fixing the Wedi boards to the wood joists? and also the best fixings to fix the Wedi boards to the thermalite blocks? Thanks
Hello, if you mean studwork and not joists then any screw will do as long as they're of a sufficient length and are able to fit through the washer. I tend to just use Goldscrews for nearly everything, but plasterboard screws would be fine also. If your boards are 12.5mm then a 50mm long screw will be ok - 4.0,4.5 or 5.0. As for fixing to the blocks it's just the same as I explained before but check Wedi fixing instructions.
Wedi boards are all fitted now, the floor is screed with wet under floor heating up one end and the impey aquagrade screed in place. I am ready to now tank the screws floor with the impey waterguard membrane .

Once this is done should I then use a tile decoupling membrane on top of the impey waterguard membrane as I have underfloor heating?

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