Charlie: Diaz from Manville writes in, “I just bought an older pier and beam home, and the floors are not finished. It has an OSB base, and the floor is a little bouncy, and I’d like to install tile myself.” He wants to know, “Can I install cement board?” I assume he found backer board, 1/4 or 1/2 inch on top of that. “What other options do I have for underlayment for the tile?”
Diaz
Tom: OK, I think I’d put a layer of plywood down. I don’t know the thickness of his OSB. It’s probably going to be around 3/4 of an inch. That’s your starting point for a single layer. If you put 3/4 inch OSB on 16 inch center floor joists, which he probably has, you’re going to get that trampoline effect. You’re not going to fall through, but it’s not going to hold tile well, so another layer of 3/4 inch, I would say plywood, tongue and groove plywood for flooring. Then you’re going to use a 1/4 inch square notched trowel. You put thin-set 1/4 inch backer board, 1/4 inch square notched trowel with thin-set again, and your tile, and it’ll work in those rooms. You’re going to have a little height difference between one room to the other, but it happens at a doorway where floor coverings change, and if that’s the case, your body will naturally step onto the new floor.