I am attempting to renovate my bathroom starting with the floor. The old flooring,(Tile),
Was removed exposing paper backing, and the dried glue adhesive,(Which have been removed,& the plywood flooring sanded. I would like to re-tile the floor but am uncertain
If I must install backerboard over the old flooring. I am hesitant as I am afraid raising the
Floor to high will cause problems when I re-install the toilet,(When the toilet was installed,
40 plus years ago, the plywood on which the toilet sat was partially trimmed down to allow the seating of the toilet onto the flange).
1) If I can get away without the cement backerboard, what adhesive should I use?
2) If not, how do I deal with the flange being below floor level?

First off, there are adapters available to allow you to install the WC on ceramic tile flooring. Basically they raise the flange by a small amount. Installing ceramic tire on plywood flooring requires mastic instead of cement based adhesives. I know, had to rip out about 500 sq ft in daughters new house as they did not stick. You can also get cement backer board in 1/4 inch thickness which will work just fine.

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Originally Posted by 450donn

First off, there are adapters available to allow you to install the WC on ceramic tile flooring. Basically they raise the flange by a small amount. Installing ceramic tire on plywood flooring requires mastic instead of cement based adhesives. I know, had to rip out about 500 sq ft in daughters new house as they did not stick. You can also get cement backer board in 1/4 inch thickness which will work just fine.

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I Agree with 450, I would certainly install something like hardibacker to prevent tile from cracking or grout line from cracking. As for the toilet flange (Cf) being below the floor level, they do make rings with sleeves to extend into the toilet Pipe (Cast/PVC) or what ever the case may be, but completely agree with 450 op ions.

Hope this is helpful

Fizzy;)

Cement board and Hardibacker both do come in 1/4" but that is normally for wall application, you can use it on a floor if the plywood sub is strong. If the old tile never cracked at the grout lines or through a tile then maybe your sub floor is sufficient already. You can use acrylic modified thinset, about $40 for 3.5 gal. The plumbing aisle at Home Depot has a variety of flange spacers, many look like thick PVC spacer washers. If the floor is more than 1/2" out of matching the toilet you can install an Oatey Twist-N-Set replacement PVC flange, $18