Hello all! The saga of my kitchen floor continues… after removing the Luan,then the layers of thinset, old vinyl scraps and vinyl glue, I found a destroyed layer of PDF underlayment! Today I started removing that and have finally come to the subfloor, which seems to be quarter inch ply… see picture. My question: can I lay concrete board on top of this, or do I need to add another layer of ply first? Joists are 16 in. apart
Did you mean to say three quarter inch ply? It doesn’t look like 1/4″ which would not be strong enough for any kind of sub floor but you’re good to go with 3/4″
Unlikely its 1/4″, probably 3/4″. Yes you can lay the cement board right on top but either glue or thinset down in addition to screwing. Will provide a much stronger subsurface. Also I would go around and screw in any loose or squeaky ones first.
What are you plans for the finished floor? Ie tile, hardwood flooring or vinyl… I suspect tile…
If you have more than a 3/8 gap or multiple. You probably should lay down a layer of ply wood to accommodate the gaps.
That is quarter inch plywood and you need to lay at least another half Inch plywood on top of that And then half inch cement board.