We want to put porcelain tile in our tiny bathroom (roughly 7' x 5 1/2'). We can see that what is currently there is the original yellow pine tongue and groove flooring, then plywood, then some tar-like vinyl layer, then tile. This all sits on 2 x 10 joists that span 13 feet, spaced 16" apart on center. We have ripped out the ceiling in the room below and will sister these joists, hopefully with 2x10s along the full length, to support a 300+ pound cast iron clawfoot tub. With the ceiling gone, we can see that there are some spots near each of the fixtures where the some of the original tongue and groove boards have been pulled out to make way for plumbing.
My first question is: Should we rip out everything including the yellow pine hardwood and start fresh from the joists, or rip out just the tile and plywood and build on top of the yellow pine?
My next question is that I am reading a lot about people having two layers of plywood. Why is this? I have always understood that we should use a plywood subfloor, then a cement board underlayment on thinset, and then the tile. Am I wrong? Please advise as to what thickness of the different materials I need depending on whether or not we rip out the hardwood and start fresh from the joists.
Thanks so much for your time!