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Stabilising Plasterboard Behind Shower that has Gotten Wet and Mouldy Before Re-Tiling

Postby alpinehorn » Thu Nov 12, 2015 4:56 pm

Hi, I'm new to the DIY Doctor and hoping for a solution to the following problem:
My daughter's house. The ensuite shower is leaking through to the floor onto the ceiling of the room below and on close inspection, not only the silicone sealer was in poor condition, but the grouting around the bottom row of tiles was cracked and loose, and several of the tiles are also loose. When I removed the grouting the tiles just fell off. The paper surface of the plasterboard came off with the tiles leaving the bare plaster exposed. It was damp, had black mould and is chalky. I've cleaned off the mould using white vinegar then hydrogen peroxide and the plasterboard has dried out nicely but is still chalky. What should I use to stabilise the plasterboard before re-tiling? What about masonary stabiliser or PVA? It's only the bottom row of tiles and I really don't want to take off all the tiles and re-board as this is a major job and I would need to un-plumb the shower, waste, remove the shower screen etc. Thanks. Alpinehorn
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Simply Build It

Postby katoosh525 » Fri Nov 20, 2015 9:33 am

Er.... How politely to put this.
The plasterboard will be most stable if ripped out in it's entirety, and put into a nice stable skip. From here it can do no further damage.
You should really replace it with Marmox board ( ... tion-board) or similar waterproof tile backer board, something that is actually designed to have tiles layed on it in wet areas.
This is infinitely preferable to spending the rest of your life redecorating the remainder of the house as water get's everywhere and rots the fabric.
Sorry to be the messenger.
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