Overboarding with ply for ceramic floor tiles

20 Mar 2009
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United Kingdom
im laying new ceramic floor tiles in the kitchen next week. i've already picked up some flexible adhesive and grout for wooden floors and was planning on purchasing 12mm exterior ply sheets from the local timber mearchant tomorrow. however, a mate at works just told me he has a load of 9mm ply sheets that i can have for free left over from boarding his loft (reckon it would save me £100 as its a large kitchen). my kitchen floor boards are pretty sound so i think i could probably get away with 9mm but he's not sure if the ply he has is exterior grade! is the ply likely to warp if its just regular ply? i have some floor tile primer/sealant (not pva) if that matters.

thanks in advance
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might be fine, might not. 12mm is the thinnest i could suggest if you were at my counter.

I suppose you need to weigh up the savings against the risk. Personally i perfer 6mm backerboard every time.
i was more worried that the ply may not be exterior grade and that it could warp/bubble when the adhesive is spread on to it. the floor is pretty solid/level (new'ish house) so although id have used 12mm i think 9mm would be ok. do yuo think the primer/sealant would prevent the ply (assuming its not exterior grade) from warping or should i just go by some wb ply.
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I would have thought so. You shouldnt prime the face of the board your tiling though.

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