Doing a small bath room 52X76 in. The sub floor is 1X4 about 30 -40 years old. I have read to put tar paper down and that I can use chicken wire stapled to the floor. Instead of the chicken wire I was maybe thinking of using 1/4 in cement board. I am putting Pex tubing on top of the chicken wire or cement board. What would be the minimum thickness of the mud job. Height is a problem. Should I use bags of mortar mix or some thing else.

We are redoing a small bathroom, attempted to get up existing original 1 inch ceramic tiles, and has been IMPOSSIBLE. We are now planning to just tile over as the floor is solid and quite level, but now we need to level out the area we damaged (about a square foot or so) trying to rip up the old tile, as well as the gaps along the walls where we removed the old wall tiles. Main question, do we have to put down a barrier against the tub ( which will be refinished in the end) or can the self leveler be allowed to run right up against the tub? As far as the walls outside the shower, they are not being retiled (just repaired and painted) , is a barrier needed to prevent self leveler from leaking beneath the wallboards? Any advice?