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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?

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I would not leave a gap, and use screws long enough to reach through the plywood through the backer board. Make sure the flange is well supported or you'll have problems with it down the road if not immediately.

Maybe an even better solution would be to have plywood of the right thickness span the gap between the subfloor and the flange, and still use longer screws that will reach the subfloor. Cement backer board tends to be weak at its edges and may not provide the support the flange needs. Plywood on the other hand is very strong at its edges and should hold up marvelously. This small piece of plywood can be kept inside the area that the toilet bowl covers so you won't have to put tiles over it or anything. You might want some plastic shims on hand for the job too, in case the plywood and flange don't meet nicely. Good luck.

  • Sounds good, I'm going to use the Set-Rite kit, using their spacer below. I'm only using it because the flange sits about flush with the finished floor, and I think it should be a bit higher to prevent leakage this time. – Jon Fournier Apr 9 '15 at 17:13

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