Slate on 1/4 inch Cement Board?


Old 09-23-05, 07:27 PM
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Slate on 1/4 inch Cement Board?

I have a 'height problem' - to meet up nicely with the wood (oak) edge around the 2nd floor opening to my new spiral staircase, I need to use something thinner than 1/2" cement board under the slate floor I want to install. The first layer of sub floor is 1/2" OSB. I was going to use 1/2 cement board but it brings the slate up higher than the round opening. Can I use 1/4" cement board on the floor? The size of the area to be covered with slate is 6' x 14' and, of course, around the stairway. Thank you...
Old 09-23-05, 08:18 PM
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I don't think stone will last over any OSB floor.
Old 09-23-05, 08:31 PM
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Hmmm...maybe I misspoke..the first subfloor is probably plywood. Can I put 1/4" cement board over the plywood and then put down my tile.
Old 09-24-05, 06:26 AM
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If the plywood was 3/4" you might get away with it but at 1/2" the subfloor does not have enough support between joists. The flooring could flex enough to cause the tile to break. Of course, this is predicated on the joists being set at 16" on center. If they are wider than that you would need upwards of 1 & 1/2" of plywood before the cement board could go in.
Old 09-25-05, 03:31 AM
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Ish, Slate (or any stone) requires a very stiff subfloor. Twice as much as a ceramic or porcelain tile.

What exactly do you have now for sub-flooring, and what is the size, spacing and clear span of the floor "joists"???
Old 09-25-05, 04:34 PM
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1/2" OSB is fine for a subfloor, I only hope that's not all you have, it's probably thicker and you'll need another laye of 1/2" plywood, then a CBU or membrane, also as stated before, need to know the measurements of that joist system before continuing.

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