This is my 1st post here and also my 1st time renovating a bathroom. I have demo'd the bathtub and tile walls in my bathroom. I am planning to install a new bathtub with CBU (concrete backer board) for the walls (+aquadefense for waterproofing membrane).

The old bathtub had bullnose tiles that extended past the tub, which led to me cutting the wall past the perimeter stud.

as you can see here

enter image description here

I plan on installing the CBU up to the perimeter of the tub which will end on the stud and installing a patch of drywall to butt up to the CBU. I want a nice clean line of tile ending at the edge of the tub.

I'm struggling to figure out how I will tape the drywall/CBU joint. I imagine it would be difficult to do so since the joint won't be on a stud. The cut edge of the drywall is already flimsy since there's no support behind it. My fear is that I'd tear the drywall when I go to tape the joint.

  • A) Please edit to define what "CBU" is. B) Yes, all wall board joints should end on studs so each side is supported, however, I'm not sure how you'd end up "tearing" the drywall by taping it - please expand on that concern. There are options for drywall joints "hanging in the air", but that may depend on what CBU is.
    – FreeMan
    Dec 22, 2023 at 14:30
  • 1
    I have updated the post to call out that CBU was short for concrete backer board. I’m using durock boards for the alcove walls.
    – Niko
    Dec 22, 2023 at 15:31

2 Answers 2


It pretty much depends on the tile you're using. I would strongly suggest laying tile well beyond the edge of the tub, down to the floor. The tub/wall interface, in my experience, is just as much a "wet" area as further in, and drywall there is not appropriate. The exact transition edge should make for a nice tile layout, with no unnecessary/awkward cuts. It is no big deal to add suitable framing to back up your boards, you should not limit yourself to the existing studwork.

  • That’s a good point. I was set on terminating the tile at the tub edge but I’ll go out a few inches past to address the moisture concern.
    – Niko
    Dec 22, 2023 at 17:12

In the case of a retrofit like this I've found it useful to let the drywall extend under the tile slightly--say 4". This dramatically reduces the amount of repair necessary. You can just roughly tape the joint with mesh and bury it. You wouldn't expect much moisture out near the edges, so that's not really a concern.

If it's a new install or you already have a large opening, it doesn't much matter. You can tape the joints as normal and skim any protruding cement board to give it a smooth texture. If it's simpler and more robust to use larger cement board patches, just do that.

You can float backing rather than trying to fasten it into the framing where your joints are between studs. Flat 2x4 or scrap plywood work well.


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