We took up old ceramic tile and found no cement board or other underlayment material underneath. However, I did find that the previous installer had put another sheet of 1/2 plywood over the 3/4 inch plywood subfloor. No nails or screws in that top sheet of plywood. Guessing they just glued it to the 3/4 inch subfloor.
Is this adequate to install new 12 x 24 inch porcelain tile if I screw that top plywood onto the subfloor, ensuring the screws are every 6 to 8 inches apart and not screwed into the joist?
Or, do I need to get rid of that 1/2 plywood sheet and install cement board, or something like Ditra?
Thank you. Kicknback1