How should I prepare a sub-floor for porcelain tile?

Question

I am removing a laminate tile floor. There looks to be 2 layers of 3/4" Plywood as the sub-floor. Do I remove 1 layer of Plywood and install 1/2" concrete board or leave the plywood and install 1/4" concrete board on top of the plywood before installing the porcelain tile floor? My concern is that if I leave the existing sub-floor material I am going to have a ½” rise in the floor from one room to another.

Answer 1

wirelath nailed over the plywood(overlapping the lath 2",use paper backed lath to avoid moisture of setting/grout materials)nail or staple(pneumatic,not a hand staple)in a 8"x8" grid.wire acts as a trampoline,the thinset gets into the mesh but won't twist when the plywood deflects.normal thin-set is fine in the application(unless a modified is needed for the tile).

Answer 2

Although cement backer board is an ideal substrate for tile, you could bond directly to the existing plywood if it is clean, flat and strong (little or no flex); this is acceptable for areas that see only incidental moisture. There are polymer fortified thin-set mortars specifically designed for direct application to sound plywood flooring that does not exceed maximum deflection specs. I have had very good results, proper application is key. Check it out: fortified thin-set mortar –

1/4" cement backer will conform to irregularities in the floor (high/low spots), so if the existing plywood is not smooth and flat I would probably remove the top plywood layer and use 1/2" backer board to give the smoothest flattest surface.