subfloor for extra large tiles

Old 01-18-09, 09:40 AM
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subfloor for extra large tiles


We are renovating an older home. (well not that old, built in 1975). We want to tile with extra large tiles for a contemporary look. The tiles desired is 20 inch x 40 inch. We might even consider 40 inch x 40 inch. The existing floor is 5/8 plywood T&G. Joists are 2x10 spruce spaced at 16 inch center. We were thinking of putting another 5/8 plywood T&G glued and screwed but the floor is very unleveled where certain spots would not allow for more then 1/8 extra thinkness to make it all level so we really can't put the 5/8 in those spots. We were thinking of not adding plywood in those high spots and simply adding self leveling cement to make it even to the plywood on all sides. Certain spots would only have 1/8 of cement and then we would tile over it. we would reinforce the Joist but putting "X" braises.

My question is, will this be strong enough so the tiles won't break? a little more tidbit of information is that we are considering radiant floors so after putting in the radiant floor (electrical) we would add another layer of self leveling cement of approximately 1/4 inch everywhere which probably adds another level of straight. If that can't work, any possible solution out there.

Any thoughts anyone?
Old 01-18-09, 07:23 PM
Join Date: May 2007
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That floor sounds like it isn't even close to being flat enough to consider any other method than a real mud job.

Ceramic tiles require a flat floor. Those monsters you're considering require an almost perfect floor. Normally the floor needs to be "within 1/4" in 10 ft. and 1/16" in 12 inches of the required plane". With large tiles it should be within 1/8" in 10 ft. of perfect flat or better.

There is also the issue of the subfloor and the joists system which we need more info about. Doesn't sound like a DIY job to me.


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