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Unread 03-02-2021, 02:41 PM   #1
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Join Date: Mar 2021
Location: Portland, OR
Posts: 7
Zoe's DIY Bathroom - Dilemmas abound!


I am a new homeowner in the process of finishing a bathroom. When we bought the house, the bathroom plumbing and electrical was already roughed in, so we are finishing it. I have decided to go with a Kerdi Schluter shower system, and have everything ready to go (I think). There is so much great info out there from the company themselves and this forum that I thought it was an easy decision.

The one question I can't find a definite answer to (even after speaking to customer service themselves!) is what to do about the cement backerboard seams in the shower. I know you can use drywall, but I didn't want to, and went with CBU instead (particularly because when we did the drywall install, I wasn't sure which shower system we would proceed with). Rather than RedGard the walls and mix systems, I decided to use the Kerdi membrane on the walls.

However, this is meant to be applied with unmodified thin-set, and everything I read says to tape the CBU seams with fiberglass tape and modified thin-set. Schluter says drywall seams don't need to be taped, but did not have any info for CBU seams. The rep told me that the tape will repel thin-set, which seems incorrect since the tape is made to be covered with thin-set, and since it is a different tape than the drywall tape referenced in the handbook section they referred me to.

So, do I:

1) Tape and mud the seams with fiberglass mesh tape and modified thin-set, wait for it to dry and risk creating speedbumps when I apply the unmodified and the Kerdi?

2) Tape and mud the seams with fiberglass mesh tape and unmodified thin-set at the same time as I am applying the Kerdi to avoid speedbumps at the seams?

3) Leave the seams open as advised by the Schluter rep and apply Kerdi over top, risking the crack lines across all the open seams?

Thanks in advance for any input and I apologize profusely if this question has been addressed elsewhere - I searched high and low but fully admit I may well have missed it. That said, I wanted to go ahead and create an account here either way as I do have some questions about the flooring we will be installing after the shower is installed, too.


Last edited by ZoeJR; 03-02-2021 at 03:54 PM. Reason: Edited to clarify what I mean by "Tape and mud the seams", as I do NOT intend to use drywall mud or drywall tape.
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