Tiling Over Plasterboard


Postby claire.arnold » Fri Aug 03, 2007 9:22 am

Hi, I am having to build a stud wall in my bathroom behind the toilet cistern as the soil pipe is too far away from the wall to fit a closed-coupled toilet. I am building a wooden frame & then nailing the plasterboard to the frame. I would like to know if it's ok to tile straight over the plasterboard or do I have to plaster it/treat it properly first? Also, will the tiled surface be strong enough to hold the cistern? Thanks very much.
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Postby slapdash » Mon Sep 03, 2007 3:57 pm

The plasterboard should be given a couple of coats of PVA to just seal the surface. That should allow the tile adhesive to grab hold. There's no need to skim coat with plaster or any of that; once it's under the tiles who will know? Course you'll never get the tiles [i]off [/i]again without destroying the surface but that's the next guy's problem...

Before closing the frame with the plasterboard you could nail in an extra wood stud for support just where the cistern needs it. With a close-coupled system the support isn't taking the weight just balancing the cistern, but not a good idea to hang it off a piece of plasterboard and your shiny new tiles.
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Postby satilaboy » Tue Oct 16, 2007 5:13 pm

[quote="slapdash"]The plasterboard should be given a couple of coats of PVA to just seal the surface. That should allow the tile adhesive to grab hold. There's no need to skim coat with plaster or any of that; once it's under the tiles who will know? Course you'll never get the tiles [i]off [/i]again without destroying the surface but that's the next guy's problem...]/quote]

we are fitting a new kitchen soon and so recently stripped off the old kitchen tiles. problem was it left all sorts of damage to the platerboard underneath.

is there any way round this?

when we re-tile we only plan to go a couple of rows high (from worktop up). I thought perhaps a thin sheet of hardboard or similar attached to the wall, a couple of coats of PVA onto this and then tile onto this - then in a couple of years we can take the tiles off without damaging the plasterboard, and re tile.

are there any potential problems by going this route???
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Postby Burnsy » Tue Jan 08, 2008 10:04 pm

Never PVA the substrate behind tiles, always make sure that it is PROFESSIONAL TILERS PRIMER.

When you treat a surface with PVA it partly soaks in and partly sits on the surface of the substrate much in the same way as wallpaper paste.

If PVA gets wet it becomes slightly live again, it doesn't completely return to it's liquid state but it becomes sticky.

When you spread tile adhesive onto the wall, the water in the adhesive makes the PVA live and stops the adhesive from penetrating the substrate and providing a mechanical grip. Basically your tiles, grout and adhesive are being held to the wall by a thin layer of PVA.

Most tile adhesive works by crystallising when it sets (some are slightly different such as epoxy based ones) but generally they all work the same way. Once the adhesive starts to set crystals from and expand into any imperfections in the substrate surface (at a microscopic level) to create a grip. PVA stops this process by creating a barrier between the substrate and the tile adhesive.

Ok so what's the difference between this a primer, well basically the tile manufacturers primers soak right in to the substrate and stop the sponge like "draw "effect but they don't coat the surface in any way, they are an impregnator as opposed to a barrier. They also stop a chemical reaction occurring between the cement based adhesive and a plaster substrate, a known problem know as "Ettringite failure"

So only use PVA before tiling if the adhesive manufacturer specifies it in the instructions."

If you are tiling onto plaster board with a ready mixed adhesive there is no need to primer or pva. If you are using a cement based adhesive, then use a Primer as this will also help stop the adhesive recating with the gypsum in the plaster

Cheers
Last edited by Burnsy on Tue Jan 15, 2008 10:07 am, edited 1 time in total.
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Postby kbrownie » Wed Jan 09, 2008 12:08 am

Hi claire.arnold.
Lots of good advise been given, but to answer your question, I think satilaboy. Gave you a great solution. Fix hardboard on to wall before tiling then tile on to that. Then when it is time for a change and tiles need replacing. It will be easier to remove tiles without damaging plasterboard. (Slapdash! I now know where you got your name from next mans problem, tut tut!)
Best of luck
KB
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