I recently removed my toilet and saw that a couple tiles underneath it were cracked, and on removing those tiles found the plywood beneath the tiles had rotted out. So I removed any tiles under the bad plywood and removed the plywood down to the sub floor plywood, which is in good shape.
My plan is to cut a piece of cement board to accommodate the new tiles, but I am not certain of how to secure the closet flange. Right now only one of the four screws is still intact, presumably due to the rotting of the plywood.
Do I use cement board screws and secure the flange down on the backer board? Or do I leave a gap and try to screw the flange down into the plywood?