Mud Question

[mariner72]

35 year old home - tore out whole room - there was a 30 inch tub in place and the 15 inch center drain landed just clearing inside a joist - floor was mudded previously - floor is off level and has dips on both side of the room - I will mud this room again rather than deal with it - Ive had good luck with mudding - my question is
The wife wants a 32 inch deep soaker tub - which puts my drain on 16 center of the joist - just great - I've installed the same tub once before 32x60 Jacuzzi Linea tub and they give you some room off the floor drain to floor and want to add at the tub only 3/4 inch plywood over 1/2 inch that is there - reason being 2 fold - support and 2nd raise the tub - to level the tub I will have to lift it 1/2 inch at the drain wall - the math is sub floor 1/2 inch, + 3/4 ply added & 1/2 inch lift to level tub and Tub room will give me enough to keep the drain off the joist. I will also add a bed of cement under the tub when I set it level
So my question is regarding the mud which may be at least 1 1/4 at the tub will there be any issues at the tub when mudding up to the 3/4 inch plywood edge should I keep the mud off the plywood - is it ok just to add 3/4 inch ply under the bath tub only and mud up to it or do the whole room in 3/4 , Thanks for any help with this - pics attached

[Davy]

You said the floor was previously mudded. Was that over 1/2 inch ply? I would add 5/8 or 3/4 over the 1/2 inch, then the mud bed. Is that possible?

[mariner72]

There was a tub with a molded surround in there - it was not mudded under the tub - up to the tub - the entire bath room has been gutted and yes I can swap everything out to 5/8 or 3/4 - the problem is on both sides of he room I have joists that are uneven - almost as if 2 of the crowns were flipped so I have high & low spots on both sides of the room- which is why I want to mud the room - they say you can't plane the high spots and you should not shim the low spots. one other question is has anyone ever mudded under the tub to level the whole room and then put the mortar under the tub when you install it - or should you always intall the tub on plywood substrate ?

[Davy]

I would add more plywood to what you have without shimming. Let the mud do the leveling. With added plywood, how thick can you get the mud?

I would add plywood under the tub area as well along with felt paper and lath. You can level the bath floor up to the tub area. Depending on your tub, some instructions say to set the tub in a wet bed of cement for support. You can do that on top of the lath if needed.