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4" hardwood floor boards mounted on a poorly-designed frame made out of whatever wood the constructor had lying around it seems. There's a lot of bounce, some boards even drooping 1/2" when walking on them.

I'm thinking of tiling over with 12" square tiles, maybe 16".

I've never used self-leveling compound before. Would it be suitable to level the floor with this before lining it with 1/4" cement board prior to tiling, or would it seep through gaps between the floorboards?

With the ceiling height already being illegally low at 7', I'm trying not to raise the height of the floor too much.

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up vote 12 down vote accepted

Anything rigid you put over a flimsy structure will be destroyed over time because it won't have the support it needs. Most tiles (except plastic/vinyl) don't handle bending well.

Self leveling compound doesn't add rigidity, it just makes a smooth top surface.

You need to fix the structure first. That means going down before you go up.

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I was hoping the cement board would add enough rigidity, bracing the bad boards to their more sturdy neighbors. – jontyc Feb 13 '12 at 13:57
No, cement board won't work. You need to get rid of all of the deflection. Fix the structure, then put down a tongue-and-groove panel subfloor material. – Karl Katzke Feb 13 '12 at 15:04
Greebo is right: Our first tile project was on a sheet of cement board under a woodstove. The floor is not rigid, and sure enough, the tiles popped off pretty quickly. – Jay Bazuzi Feb 14 '12 at 7:41

You must reinforce the existing structure to make a sound, fairly rigid subfloor before you put anything else down. Depending on how things are built, you may need to add more support to out the subfloor on.

I'd look at putting down 3/4" OSB and then tiling over the top of that.

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OSB will still bend and flex if the structure underneath of it doesn't offer enough support. – The Evil Greebo Feb 13 '12 at 19:54
Absolutely. Make sure the structure is sturdy first. – Peter Loron Feb 13 '12 at 21:28

You will need to take up the existing floor and replace with new ply or it will never hold the tile.

If hight is a issue you can put 1/2" sanded cdx to tile on instead of cbu board but will still need 3/4" unsanded ply under the 1/2".

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