I have been trying to find info on my issue. My subfloor is 3/4 inch planks over 16" on center joists. The planks are not tongue and grove they are just planks with a small space in between them. My question is that I plan on putting down ceramic tile for the bathroom floor and was wondering what I should do to put the cement board down. Should I (1) put down a mortar and not worry about the cracks in the subfloor and then put then durock overtop and screw down. or (2) just lay the durock down and screw the recommended amount or (3) something completely different.
I would contact USG (the maker) and ask them what they think about additional underlayment.
old plank floors says to me this is in an older house, and those planks and everything they rest on is going to move. I'd do a 3/4 inch plywood underlayment and then the Durock, and then the tile myself.
sig: if this is a new economy, how come they still want my old-fashioned money?
Posts: 5389 | Location: North Burbs, MN | Registered: Mar 14, 2007
You need to do a plywood layer on top of the existing plank subfloor. It doesn't have to be 3/4". 1/2" will be fine. 3/8" will even work but you'll need a closer nailing pattern than 1/2". Unless height is an issue, I'd go with 1/2"
Adding the plywood layer creates a stable base for the cement board. Cement board has no real strength and cannot compensate for any movement or cupping that is bound to happen between a plank subfloor. Once you securely fasten the plywood, either with ring-shank nails or screws, then the backer can be applied in a mortar base.