In the middle of a bathroom re-model and at the point of replacing the floor.

Removed the existing vinyl tile from the floor and a bit confused about what is underneath. Not sure what is needed for it to support ceramic tile. Specifically, this mosaic tile.

enter image description here This is what the subfloor looks like after the vinyl removal.

It's difficult to determine the type of wood. There is either a membrane/underlayment or sealant of some kind that stayed on the floor after the vinyl was removed. There's only a few spots peaking through.

I'm hesitant to pry off this "membrane" in case this material might help in installing the ceramic on the subfloor without requiring another underlayment like Ditra, Easymat or backerboard.

There is very little extra space between the exterior floor and the bathroom that raising it with any of those options will add too much of a height disparity.

My questions are:

  1. What is the wood used and the "membrane" on top?
  2. Can I install tile on top (with thinset) or is an additional underlayment required?
  3. If it's required, can something like Redgard or self-levelling cement be used to keep the height increase to an absolute minimum?

This is my first time doing any flooring so I appreciate the help. Thanks!

  • 3
    Looks Like OSB (or some plywood, some OSB) with floor leveling compound on top.
    – Ecnerwal
    Feb 22, 2017 at 1:51

1 Answer 1


I agree with OSB and leveling compound. I know it would be more work but I would see if the OSB is a underlayment and possibly only 3/8" thick, chip up a small hole where it would need to be patched if you use this surface. If a thin underlayment pull it up and replace with cement board. Cement board will not swell and fall apart if moisture gets under the tile like OSB will. Another advantage to cement board is it will be a better base for the tile making the tile stronger than on wood. I have dropped small tools and broken tiles in the past, but have found impacts on tile set on cement board with thinset resists breaking much better. If you want to stay with the current base verify the "leveling compound is secure not loose and breaking up. Clean out all the loose stuff and clean up as much of the dust as possible. Once clean use some leveling compound mortar to repair the surface so it is smooth. Once the floor repair is dry it would be time to tile.

  • Thanks. I ended up taking it off. It's more than 3/8" thick (5/8") so it is more than an underlayment, but there's subfloor underneath. Easier to start here instead with cement board. Thanks!
    – d_ethier
    Feb 22, 2017 at 17:09

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