tiling over porcelain

Postby carlostiles » Mon Sep 07, 2009 12:32 pm


I have laid some large (600 x 600) porcelain tiles on my kitchen floor over underfloor heating and 18mm chipboard, using the suitable adhesive and grout. I've noticed that close to half of the tiles are loose and 'bouncing', mainly in the corners producing a 'hollow' sound underneath. I know the chipboard was firmly glued and screwed down and that this isn't causing the problem (the loose tiles are scattered about the kitchen).

My first thought was to take them up and replace them. But i'm worried about damaging the UFH (its electric). It's also close to half the floor area (total area 18sq metres). So my second thought was to tile again over the top of the porcelain tiles. My questions are: Can i tile over porcelain? Which adhesive do i use? Do i need to prime the tiles with anything first? what about the 'loose' tiles underneath?

Many thanks in advance of any help,

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Joined: Mon Sep 07, 2009 12:22 pm


Simply Build It

Postby plumbbob » Tue Sep 08, 2009 10:34 pm

If many of the tiles are already loose, I don't understand how you think tiling over them is going to solve any problem at all! In fact it is just going to compound the problem as the new tiles won't stick either because the tiles they will be stuck to are unsound and whatever caused those to fail will continue and simply affect the new tiles. The final result will be your having two sets of tiles to bin.

Of course the original tiles shouldn't move so either the plywood was not thick enough, wasn't fixed securely or an inferior adhesive was used.

To be honest, I think you have serious problems that almost certainly cannot be rectified. Without doubt, if this had been professionally installed, it would all be coming up and be completely replaced FOC.

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Joined: Wed May 07, 2008 9:59 pm

Postby carlostiles » Fri Sep 11, 2009 2:06 pm

Ok, i've taken up the tiles and the UFH and scrapped all the adhesive off of the chipboard. UFH still works, and about 25 tiles have been salvaged, though i'll not be using them again!

So i'm back to 18mm t&g chipboard on top of 50mm battens at 400mm centres, with celotex insulation in between the battens. 100mm concrete under that.

My first job will be to screw a whole lot more screws through the chipboard into the battens. There's a little movement if i jump up and down, but very little. Better to be safe than sorry.

After that i'll relay the UFH, and cover it with 'solo' floor levelling compound to about 5mm depth. Apparently it can be used on wood floors and is compatible with UFH. I think then i'll be ready with a flexi adhesive and a new set of (smaller) tiles to go again, and then flexi grout.

Can anybody confirm if this is ok before i start? I really don't want to be doing this all again!


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Joined: Mon Sep 07, 2009 12:22 pm

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