Any advice on best way to fill a hole in my bathroom floor?
I pulled up the 60's era blue tile to find original white tile underneath. In one area, the original tile was loose so I pulled it up to reveal a hole filled with crumbling old … cement? Plaster? Whatever it was they laid down as the subfloor to the first layer of tile.
My question: can I just fill the hole with piece of wood, use spray foam around it, trim when dry, and then proceed with the leveling underlayment? Will the underlayment react badly with the dried foam? I don't want to use anything too wet or heavy in the hole as the kitchen ceiling drywall is directly underneath it.
Ideas welcome! And pictures attached.