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I'm installing waterproof hardiebacker in a shower alcove. The shower pan has a flange that is 1/4" wide. If I installed the hardiebacker directly onto the flange, in some places the hardiebacker would be flush with the flange and in some cases it would be slightly proud of the flange. For various reasons, I cannot shim the walls to get the hardiebacker inside the flange. The question is, on these facts, the best way to seal the seam between the two:

  1. leave 1/8 inch gap and caulk with silicone
  2. leave 1/8 inch gap and mesh tape and thinset the gap and then redgard over the seam
  3. kerdiband
  4. use continuous window flashing all the way around that would extend from the inside of the flange and behind the hardieback about 4 inches up the studs/blocking
  5. put silicone on the flange and then install the hardiebacker directly on top of the silicone (essentially no gap)
  6. something else?

I actually have some 6" butyl adhesive window flashing but I'd rather use whatever method is the best in this situation (again, without shimming the walls out).

Thanks.

Dean

Dean
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  • Does the shower pan manufacturer instructions provide any information? I wouldn't be surprised if they recommendations or warranty requirements on the pan to wall joint. – blarg Feb 02 '23 at 00:14
  • No. Shower pan manufacturer doesn't have any instructions whatsoever for the wall joint. The instructions for installing the pan itself were pretty minimal. – Dean Feb 02 '23 at 02:02

1 Answers1

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I would use your option #5 but use polyester caulk such as Vulkem. The polyester is much better than silicone. Totally waterproof, and good for about 15 years.

RMDman
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