I am in the process of installing a shower stall in my downstairs bathroom that will only be used when we have guests. The bathroom has a solid oak floor 3/4" that is prefinished. Can I lay a mortar bed on top of the finished floor to put the shower reciever on? Taking it down to subfloor is not possible and the finished floor is not level.
Thanks,
Greg

I would not recommend going that. Solid oak floors are not very stable and if there were even the smallest of leaks, that oak floor could expand greatly, ruining your tile mortar bed. Surely there must be a way to just cut out that one section. Just use a skill saw and a sawzall to cut out that oak flooring. Make sure you do NOT cut into or through your subfloors

What if I put down a thin piece of plywood on top of the finished floor? The oak is not stable, I agree. It expands and contracts, warps and then flattens out with the seasons (I live in Vermont). However, this is a mortar bed for a shower kit (kohler), and the reciever is a one piece unit. Does that make stability less of an issue? Would plywood over it give me the stability I need?

is this a fiberglass base that's being installed?

also, how are you running the drain for it?

Basically, yes it is a composite by kohler called Vicrell, but to me it feels like fiberglass, and it does seem a little on the brittle side overall. I used a 4.5" hole saw to cut the drainhole through the floor, and have a Oatey shower drain kit mounted in the reciever. I have access from below in the basement and will complete the plumbing there after installation.