I just ripped out the original tile and backer board on a secondary bathroom in my home and now it's time to put the new stuff up and I'm a bit stumped. The backer board was originally installed on top of the drywall which is causing a spacing problem. My tub is an old cast iron tub and it's 59 5/8" long. The opening stud to stud varies from 61" to 61 3/8".
I've checked out this question and answer and I'm trying to do what is illustrated in the first drawing, but my backer board would align behind the tub flange. On the faucet side, I could easily install shims/furring strips to properly align the backer board with the tub as the wall only extends 6" past the tub.
The other wall is the problem. Since there was drywall on top of the studs and then backer board on top of it, if I use shims there, I'll end up with my backerboard coming out on top of the drywall that continues down the rest of the wall. The original tile used bullnose trim tile where the backer board transitioned back to the drywall, but the new tile doesn't have that option. What should I do?