Maximum "void" under cement under layment

Hello all. I'm deep in my bathroom remodel and am wondering how big a hole in the subfloor would be acceptable without compromising the tile floor. Specifically, I removed a 2 inch PVC drain and am left with a 2.5 inch hole in the 3/4 inch plywood subfloor. I plan on using 1 ft square tiles. Would this hole, under my cement underlayment, be a problem? I can't patch it from below, so I'd have to cut out a large area, add bracing, and replace with new plywood. My joists are 2x12, 16 inch OC. Thanks.

I'd be somewhat worried. CBU isn't structural. You might want to ask this question over at www.johnbridge.com. As a general rule, on a floor tile, you want a minimum of 80% thinset coverage (ideally, 100% support) which assumes a 100% subfloor. The biggest worry would be if someone in say high heels stood just in the right position...but see what the tile experts have to say on the referenced site.

tile

Place a piece of sheet metal over the hole and then tile it.

hj said:

Place a piece of sheet metal over the hole and then tile it.

Click to expand...

16 guage or heavier.

You did not state where the hole is located. If it is under a sink, tub, or vanity where no weight will be placed on it, the CBU should be fine. Anywhere else, the sheet metal will work.

Thanks for the responses. The hole is in a traffic area. I hadn't thought about sheet metal. Great idea.