Suitable subfloor for meshed mosaic tile


Old 11-20-04, 09:07 AM
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Suitable subfloor for meshed mosaic tile

I want to install 12" x 12" mesh sheets of 2" mosaic tile on the floor of an upstairs bathroom. The floor substrate is 19/32" Potlatch OxBoard, laid across 12" centers, and is in excellent condition, not giving or flexing anywhere.

I'm gonna pull up the existing carpet remnant and linoleum (laid directly upon the OxBoard), neither of which is glued or fastened in place. I'm not going to remove the full length tub/shower surround (right side). I'm not going to remove the custom, full length vanity (left side). I may/may not remove the toilet (ahead along the back) depending upon answers here.

What I'm left with is almost an 8' x 4' working/walking area onto which I want to install these mesh sheets of mosaic tile.

Any recommendations on what I should use as the subfloor for this tiling?

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Old 11-20-04, 09:29 AM
Join Date: Oct 2004
Location: New Jersey
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Thinset will not adhere to osb. The only option to go over osb with thinset is to use Ditra underlayment but that requirers 23/32" osb and you are just shy of the 5/8 range. Given you are at 12" oc, you may want to contact them and see if they will warrant it for your application. Go to and they can let you know if they will back it up in your situation, as well as direct you to dealers in your area. You are also under the spec for cement board, which requires minimum 5/8" subfloor with 1/2" cement board set in thinset and screwed down or 3/4" subfloor with 1/4" cemtent board set in thinset and screwed down. To tile, you will need to add a minimum of 3/8" exterior grad ply screwed down to the first layer and no into joists every 6-8" oc over the entire face of the board, use cc plugged or better graded plywood at which point you would be fine with 1/4" cement baord thinsetted and screwed down. This will raise your floor height about 11/16" before the tile height. You will need to pull up the toilet obviously, but can end your additional subfloor layers at the tub and caulk the gap before tiling as well as after setting your tile but after tiling, you can use a color texture matched caulk along any area that there is tile ending without moulding. Maintain about 3/16-1/4" gap between your added subfloor layers and any wall and at the toilet flange. You may need to use a flange extender when resetting your toilet.
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