I am in the middle of remodeling a bathroom in a house I just purchased.
I tore out the old tile and found it was on green board, and behind the green board there was drywall. I am assuming the reason for the drywall behind the green board is because there was such a gap between the studs and the tub.

So, what I have done is installed 1/2" green board around the entire tub and then installed 1/4" hardibacker over the top of that so the hardibacker lines up perfect with the tub flange. (I know I could have probably shimmed out the studs to close the gap but its too late for that now.)

I then plan to tape and thinset the joints in the cement board, and then waterproof the hardibacker with Mapelastic Aquadefense (similar to Redgard).

Do you guys think that this is going to be okay? I was worried about creating a "mold sandwich" as they call it, but the green board is not a vapor barrier, so if I just apply the Aquadefense to the cement board this set up should be okay right? Hope you say yes! Thanks!

 

I would have used lattice slats (1/4") glued and nailed as shims direct to the studs and 1/2" cement underlayment on top.. 1/4" underlayment is for flooring applications where it is set in a bed of mortar and is not used as a structural element. Concern with tile is and always been movement. Not sure if your sandwich will stand up over time. Anyway, I would not consider greenboard to be the best furring solution. Even those who built the shower before you had the sense to use 2 sheets (1" thick) under the tile.

Tell us more how you plan to move forward with the installation? Does the tile wrap around the room or how do you plan on finishing the depth differentials between the tiled walls and the sheetrocked walls? Type and size of tile, size of trowel, type of mortar etc? Taking the tile all the way to the floor, or stopping at the flange? Pictures would be great.

 

Yeah if I could go back i would have shimmed out the studs, but the guy who was helping me said the green board would be fine, so that is the route we ended up going. No the tile does not wrap around the room, tub surround only, stopping at the flange.

We put 1/4" drywall over the rest of the bathroom because the drywall was really messed up from the vinyl paper we took off. So the hardibacker and the drywall in the bathroom are flush so there are no depth differentials.

According the Hardibacker 1/4" can be used on shower walls, so I hope its okay!

I have not picked out tile yet and I guess that would determine my trowel size, I was just going to use thinset mortar from Lowes.

Thanks for the reply!