Subfloor for tile

[stephster02]

We are remodeling our kitchen. Removed old ceramic tile and 1/4 inch OSB with it. We are left with 1/2 subfloor with 5/8 inch plywood ontop of it, so a total of 1 1/8. We are looking to tile with 6x24" tiles using large tile mortar. There will be a transition to hardwood, so the level is already going to be higher which we want to keep as minimal as possible. Is what we have enough for subfloor or do we need to add back 1/4 plywood? I have also heard of ditra but not exactly sure...we also would like to keep costs down and I know that can be expensive. We just don't want to tile and have them crack. Recommendations? Are we good or do we need something else? Thank you!

[ss3964spd]

Welcome, Stephanie,

Are you certain the first layer of subfloor is 1/2"? If it is, it's not tongue and groove. Do you know if it is plywood or OSB? And the 2nd layer, certain it's 5/8" ? Is it T&G? Plywood or OSB?

Over and above that....well, under and below that, do you know what the joist structure is;? Are they 2X8's, 2X10's, something else? How about the unsupported span of those joists, as well as the spacing of those joists?

[cx]

Welcome, Stephanie.

In addition to Dan's questions I'll add the spacing of the joists?

[stephster02]

Hi all! I know for a fact those are the thicknesses as we had to replace other pieces of subfloor. They are both plywood, but I don't know if they are tounge and groove, but I don't believe so. The joist are 2x8's I believe spaced 16" apart with a span of about 11 feet.

[cx]

Entirely up to you what you tile over, Stephanie, but Dan asked for clarification of that first layer of subflooring because it is deficient, not meeting tile industry standards nor even likely your building code. We know it does not have T&G edges because you'll not find center-matched edges on engineered wood of that thickness. Essentially, that layer simply doesn't count at all, but is in the way.

The quarter-inch plywood your tile was attached to may, or may not be of a type specifically intended as a ceramic tile underlayment. If it's just an exterior glue plywood, that's also a problem. But if your previous tile installation survived, it all apparently worked one time. I would absolutely not recommend you try to make it work again, but that's entirely up to you.

Your joist structure, as described, is deficient also unless you can determine that the joists are of a very good species, grade, and condition of lumber.

My opinion; worth price charged.