Underlayment for Tile - Type of Plywood

[SDSailor]

Planning to re-tile hallway. Details as follows:

- I-Joists 19.2 inch o/c
- Subfloor 3/4 inch OSB - originally nailed so have added screws
- Underlayment (1/2 inch plywood) - planning to screw down but not into joists
- Ditra
- Ceramic tile

What kind of plywood should I use:

- Spruce, Fir or Pine?
- Does it need to be good one side?

Am in Ottawa, Canada.

Thanks for the help in advance!

[cx]

Welcome, Craig.

If you don't add that geographic location to your User Profile it'll be lost before we leave this page - and it's important.

I'm not as familiar with your CANPLY as I am with our APA down here, but what you want down here is an exterior glue plywood with no face of grade lower than C. Doesn't need to be your Douglas Fir Plywood (DFP) and could be any of the Canadian Softwood Plywoods (CSP) as far as I know. I'm not at all sure what your tile industry folks (TTMAC) specify, but you could maybe check that out.

Google up CSA 0151 and see what you can find. But, again, exterior glue and no face of grade lower than C is essentially what you're looking for. Grades AC, BC, CC down here, but I think the classification is different with Canadian plywood.

My opinion; worth price charged.

[SDSailor]

Many thanks CX! Appreciate the advice immensely.

Craig

[cx]

Craig, if you're using Ditra as your tile underlayment, that second layer of plywood is structural subflooring. My advice is still the same, but the terminology is so frequently misused in the industry, eh?

My opinion; worth price charged.

[SDSailor]

CX,

Thanks for the clarification on terminology. Just checked my local big box store and have reviewed some great information from the Canadian Wood Council (cwc.ca/wp-content/uploads/2020/04/Plywood-Grades.pdf).

I can easily get CSA 0151 (CSP) Sheathing (SHG) which has the following veneer grades: Face (C), Inner Plies (C) and Back (C). The documentation from CWC indicates this is typically used for "Roof, wall, and floor sheathing".

CSA 0151 (CSP) Select (SEL) would have a (B) grade veneer for the face, (C) for the other two veneers. CWC states it is typical for "Underlayment, combined subfloor and underlayment, sheathing, hoarding and packaging".

It seems like what I am doing (in terms of CWC language) is the "combined subfloor and underlayment" (structural sub flooring in your terms). Do I have that right and should I shop around for the SEL grade plywood?

Craig

[cx]

I'm only guessing that both are exterior glue plywoods, Craig, but I don't know how you tell from their markings.

The CCC would be adequate to your needs, if there is a difference in ease of sourcing one or the other or a major price difference. You have no need for a face grade above C and it appears all iner plies are also C grade.

My opinion; worth price charged.