New Master Bathroom Redo

[Gvernt]

Redoing our bathroom and I have a few questions. The original tile (look like 4" square tile) down for 22 years when the house was built in 1991 and has worked well (no tile cracks or grout cracks). It appears the orginal tile job was done over a plywood wood subfloor (not sure of the actual thickness until I start ripping it up) followed by 1/2" CBU. The joist below are 2 x 10 - 16" on center.

My question is when I rip this out I'm thinking of removing the tile and CBU out and replacing the CBU with 1/4" exterior plywood, modified thinset followed by 1/8" heat mat, unmodifed thinset and then 1/8" Ditra which gets me back to the original 1/2" CBU. Do you see any issues?


With regards to attaching the 1/4" exterior plywood, what would the screw pattern be and should I use liguid nail between the old sub-floor and the 1/4" exterior plywood? Thanks GaryNJ

[cx]

Welcome back, Gary.

This the same bathroom you been fixin' to work on for a few years and have a few other threads about? We like to get all the available info in one place whenever possible.

We'd need first to know what subflooring you'll end up with and its condition before advising what to install over/instead of/in addition to what you've got.

For sure you do not wanna add any 1/4" plywood of any kind to the package. If the subflooring needs some help, 3/8ths" is minimum and half-inch would be my preference.

If your subflooring is adequate (I doubt seriously it will be after removing the CBU) you could add thinner CBU if all you want is extra height and then your heating system. Far better to add more subflooring and install your heating system directly on that, presuming, of course, that the manufacturer approves that installation.

My opinion; worth price charged.

[Gvernt]

I spoke to Schluter yesterday and they prefer that I use plywood filler rather than CBU, since CBU would void the warranty when I apply Ditra. All, I want to do is introduce the heat pad without adding any additional height and I believe my original subfloor construction is fine since I haven't had any problems in the past 22 years.

[cx]

I feel sure they didn't recommend a 1/4" plywood "filler," though, did they?

I'm surprised they would tell you the CBU, properly installed, would void their Ditra warranty when installed over a radiant heating system. But that'd be between you and Herr Schluter.

And in your house with your tile and your dinero you can certainly install in any manner that makes you comfortable.

My opinion; worth price charged.

[Gvernt]

Actually, they mentioned 3/8" plywood. Anyway, what is the proper method of attaching 3/8" plywood (screw pattern and any glue)? Thanks GaryNJ

[cx]

They mentioned that because that it the absolute minimum thickness that is considered at all structural. I, again, would use nothing thinner than nominal half-inch exterior glue plywood with no face of grade lower than C.

I would suggest installing your second subflooring layer in accordance with the recommendations in this article to the extent feasible.

My opinion; worth price charged.

[Gvernt]

Thanks for the info.. I'll consider the 1/2 versus 3/8 once I see how much the original subfloor is before I make the final decision.