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Schwarzaroo 01-08-2009 02:48 PM

Preparing wood subfloor for ceramic tile
I am remodeling my kitchen and I'm about to rip out the old floor which is layer upon layer of plywood and vinyl. (I'm having the various layers of vinyl tested for asbestos now.) Anyway the house was built in 1928 and has a wooden subfloor consisting of 2 1/2" T&G planks. I'm planning on going down to the subfloor and then building back on top of that. I'm expecting to find significant issues with flatness and probably holes cut for previous electrical and plumbing configurations.

I'm going to be laying ceramic tile down, what is the best way to prepare the floor and flaten it for the tile? Self-leveling compound? Hardybacker screwed and glued to the T&G? Do I need a plywood layer on top of the sub-floor (under the backer)? I am trying to make the floor as thin as possible to flush out with the adjacent hardwood floor which is only 3/8" think layed directly on the T&G.

Thanks for the help, this website has been golden in the past!


JazMan 01-08-2009 08:17 PM

Hi Andrew,

If you want the same heights, install tile in the other room too. The kitchen will be from 5/8-3/4" higher if you go with a "thin set" method. The alternative would be a good ole-fashioned "mud-job" which would be about 1 1/2" higher.

You need to start with a flat subfloor. So repair or replace any warped or cupped boards. Re-screw every board to every joist, 2 screw per if possible. If the floor is not flat enough for the above to correct it, you may need to do more than just re-screw?

Now you have to install a proper plywood underlayment. Make it as thick as possible, but minimum 1/2", prefer 5/8" or thicker. Then comes 1/4" tile backer set in to thin set mortar and fastened etc. or you can go "Premium" with Ditra which adds only 1/8". Then the easy part, the tiles.


Schwarzaroo 01-12-2009 05:31 PM

Thanks for the suggestion on the Ditra. I think I'll go with that, found a local source that isn't too much more expensive than hardy backer. Ditra's product info states that in my situation (16' O.C. joists) I can use 19/32" or 5/8" nom. T&G subfloor. I measured the thickness of my subfloor and it looks like 13/16" T&G. I'm not too sure about the condition of the subfloor but if it turns out to be good can I just use a patching compound on top of it to flatten it out and then put the Ditra on top? Seems like this would meet Ditra's specifications. I don't want to error on the side of cracking but I don't want to add a half inch of thickness if I don't have too either. Also for consideration, the joist span is 12'. Don't know the joist spieces or grade. But the other wood I've taken out of the structure of the house (studs, etc.) is pretty strong and hard.

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