I'm trying to maximize the headroom in my basement shower. I originally planned on placing the tub on top of the subfloor and sleepers that make up the rest of the floor, but then I realized I can add about 3 inches by not doing that. The pipes actually run half in-half-out of the slab, which I "framed around" with sleepers - see here. The tub needs a mortar base, so I thought I can just put down some plastic to separate the mortar from the concrete floor and install my tub mortar base and tub directly on top. But now I'm thinking that the concrete floor is about 65 degrees in the winter, that's not exactly ideal to step on with the heat transfer.
I'm thinking I can "frame around" the pipes on the floor with 1" foam insulation (on top the 6mil plastic) and then apply my mortar directly on top of that layer to support the tub.
I think the thickness of the mortar (3" at least) should distribute weight sufficiently to support the tub while walking in it. It should be relatively solid, not like I'm walking on foam. The foam is quite rigid anyways. Under the load of a full bath tub though, should that be fine? Or should I add 1" sleepers between the insulation and the mortar, to provide a solid path to the ground? Would I need a layer of OSB over the sleepers for them to be effective, or is the mortar good enough? Or maybe I should just skip the foam all together?