1920's house with wood floors, I need to install new ceramic floor to the bathroom. Do I need to ripout the existing hardwood floor and replace it with a subfloor? Or do I put a subfloor over the hardwood? I worry about the give of the floor, although it's in fairly good shape for it's age. Or can I put a backer board right over, still the flex I am concerned about. I just want it to right the first time.
The hardwood has to go. Install new plywood underlayment of the suficient thickness over properly fastened subfloor. You probably have 1x6 on a diagonal subfloor? Come back for instructions on how and what.
Once the underlayment is installed, install a tile backer board or isolation membrane.
How about the joists? What size, type, condition, spacing and unsupported span. If this isn't right the job fails.