We're putting in a shower and I had originally found a tutorial that showed to leave ~1/8 to ~1/4 gaps around the cement board and drywall surround that would be filled with caulk to prevent water migration to drywall, should it ever get wet (we're using redgard). However, as I look more, I've found more people than not saying there should be a taped and thinsetted transition between the two. The largest gaps I have are 1/8 on a vertical seam (sides), and 1/4 on a horizontal seam (top). My thought was to caulk the lines and use bullnose tiles either completely over the caulk, or stopping at the caulk. Is there an issue with this, or should I do a thinset and tape transition to the wall?

Vertical: enter image description here

Horizontal: enter image description here

Thanks, James

  • The cement board and drywall meet between studs? That's not good. I know it's water under the bridge, but if you're not able to have two pieces of wall material meet over a stud, you should run a couple of boards down behind the drywall & the cement board and glue/nail the drywall & cement board to the wood. That would help keep the two pieces from moving wrt one another and cracking the joint.
    – SteveSh
    Dec 30, 2019 at 0:20
  • Thanks for checking, but they do! They both have decent vertical overlap (L shaped, two studs) and the spacing between studs is about 12 inches. Just doesn't show on the picture.
    – James F
    Dec 30, 2019 at 2:10
  • Well then, I would go the (gray) tape+thinset route. Then come back with something like Redgard over the joints once the thinset has cured. That's the route I took, except in my case I was butting new cement board to old plaster/cement board.
    – SteveSh
    Dec 30, 2019 at 2:21


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