The original floor in the bathroom had 1/2 plywood with about an 1 1/2 of a concrete type material which had tiles on top. Our GC said it was sandcote and was very popular in the 70's / 80's.
Joists are 2x8 16oc.
We've removed the concrete and are left with 1/2 plywood. We want to put heated floors and tile it. The 1/2 plywood seems light duty, but I was thinking because we're putting heated floors, we need to add some self leveling cement and maybe that would make it stiff enough?
Here's my approach, please correct me if I'm wrong
Screw existing 1/2 ply down
install heated flooring wire
SLC over heated flooring wire
thinset and tile
Successful installation over floor heating systems using an uncoupling membrane
Sounds good but you will need to beef up your subfloor 1/2" for plywood would allow to much flex for tile and cement board nor ditra membrane will sturdy up the floor.
My suggestion add another 1/2" of ply or replace the ply with 3/4"