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?

Diagram of the tub and walls Photo 1 Photo 2

  • @DMoore Photos added. As you can see in the 2nd photo, the drywall lines up being installed directly on top of the studs. Jan 31, 2016 at 21:07
  • What's the rest of that wall like? Obvious and most available solution is to put the drywall back how it was so you have a flat wall. Then hardi where you need it and 1/4" drywall the rest. But if there's a window or fixtures and stuff, it gets to be a lot of work.
    – jqning
    Feb 1, 2016 at 3:43
  • 1
    It's 5' give or take and runs next to the toilet. No windows or fixtures of any type. In theory, I could lay another sheet of drywall up to match it as the flooring is coming up next. Feb 1, 2016 at 5:29
  • I couldn't tell you how many times I've been told at the beginning to do a half-ass gut job, only to find when it's all said and done, that we eventually did anyway (wishing we had from the start). See my edit.
    – Mazura
    Feb 1, 2016 at 6:11

3 Answers 3


Some basic comments on what I would do:

  • First I see that you cut out a 18-24 inches beyond the tub. That is fine. But I like to see a 2x4 right where you would put a shower curtain up and another to the far right to help handle the drywall. Flip these 2x4s on their side since you have electric.

  • If your gap is too big then add 1/4" drywall behind backer. If still too big go 1/2". But I doubt that. You have backer at .42" then thinset, then tile. I am pretty sure you can cover that lip.

  • Only run a sheet of backer going straight up and down - so three feet from corner by 5 feet high. Drywall right next to it. You may need another 2x4.

  • After you put up backer and drywall I think you should be able to feather out the area just fine. If you can't you might have to lay 1/4" drywall on top of the existing.

Really this just comes down to 1/4"s. I can go into better details if you give me the exact gap, what backer you are using, what tile you are using and so on. I wouldn't worry about moving the tub though.

Note: Always install a 2x where there would logically be a shower door or curtain. Therefore if you want to install something in the future you aren't ripping out the other side of your wall or having saggy shower curtain. I would also make sure that you have 2xs and crosses set up for any sort of bars or cabinets that will go in. You cannot overframe a bathroom. Anchors fail in bathrooms before they would in other rooms.


I see that the floor tile (and possibly the plumbing, a cement bed, or whatever) prevent you from moving the tub. That was going to be my first suggestion. If it's a possibility, do that. Move it only as far as necessary toward the long wall to make it flush with the cement board.

Otherwise, I also see that you have the drywall cut back some distance on the flat wall. I'd cut it back further if you can, then intall the shims as you describe above the tub. Taper shims out on the studs outside the tub. Use a 4' or 6' level or other straightedge horizontally to find the best compromise between flat wall and parallel to the tub. (You may need to continue the taper over the tub, toward the corner, to maintain a flat wall.) Take the taper all the way to the next corner if you need to and can, or as far as possible.

It appears that you only need to gain about 1/4" (I'd eyeball the gap plus the thickness of the tub flange to be about 3/4".) That should be no trouble to taper out.

Carpentry, especially in remodel situations, is often about finding the best compromise from an aesthetic standpoint. Here, because your floor tile is diagonal, you can afford to fudge the wall a bit to make all this work together.

  • 1
    Thanks. That makes sense. Given that the flooring is coming up and it's only about 5' to the end of the wall, I may go ahead and drop another sheet of drywall on top of the existing wall so the wall really is straight since the new floor tile will be straight. Feb 1, 2016 at 5:31

OP's comment: "The flooring is coming up next."

So this is a gut job. Remove the rest of that wall's drywall and shim every stud with 2x4s attached to their sides, letting them project as needed (a six foot level is your friend here). Drywall is the enemy. Big hole/little hole = same amount of work.

Use an 'F' profile style Metal Bullnose Tile Strip. I've no affiliation with the company that make this one, I just came across it looking for standard bullnose edging. It seems to be made exactly for this situation, where you place backerboard over your existing drywall.

enter image description here


  • Thanks. I'm not sure that would look good only being on one side with the glass subway tile we are dropping in, but that's for the link anyway. Feb 1, 2016 at 5:28
  • 2
    Yeah, you have enough options that you don't need to resort to a transition strip. That's an option that a pro might use in order to keep a price low and not go tearing up walls, but DIYers have that luxury - all the time in the world and tear up whatever we want.
    – jqning
    Feb 1, 2016 at 5:40
  • @jqningq "...DIYers have that luxury - all the time in the world and tear up whatever we want...." +2
    – gnicko
    Jun 15, 2019 at 12:33

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