plywood on concrete for tile base

[tk25]

Is it OK to put non treated plywood on a basement concrete slab as a base for tile?

[Don S]

Basements absorb a lot of moisture from above and below. I would only use treated plywood, no less than 1/2 to 5/8...the few extra dollars will be worth in the long run. Then seal all edges next to wall to help guard against humidity and dampness.

Don S

[Java_Bob]

and a vapor barrier under the plywood

[HJ1]

tk

Why are you looking to put plywood over a concrete slab? If the slab is in good shape, no cracks, hasnt been painted, sealed etc. you can set the tile on the slab. You could also use an isolation membrane over the slab. I wouldnt do plywood.