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Unread 07-12-2021, 01:54 PM   #1
VapourSnow
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Wall-hung toilet on Kerdi-Board

For our remodel, we will be installing wall-hung toilets on Geberit carriers. The walls will be boarded with 3/4" (19 mm) Kerdi-Board.

Will Kerdi-Board be ok to use behind the wall-hung toilets?

Has anyone installed a wall-hung toilet using Kerdi-Board please?
(I've searched the forum, but couldn't find any threads on this.)

Any advice gratefully received. Thanks
Craig
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Unread 07-12-2021, 05:01 PM   #2
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Certainly not a problem, assuming you are attaching the toilet to studs behind the board, eh?
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Unread 07-13-2021, 11:13 AM   #3
VapourSnow
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For the Bathroom, the toilet carrier is against an external masonry wall, so will be fixed against that using anchors.

For the En-suite, the toilet is against an existing internal stud wall with 2 1/2" x 1 1/2" (63 x 38 mm) studs.
So the carrier will be attached to a Unistrut frame hidden inside the wall, with the carrier screwed at the sides to a pony wall with 4 3/4" x 1 3/4" (120 x 44 mm) studs.

Thanks
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Last edited by VapourSnow; 07-13-2021 at 01:29 PM. Reason: Improve clarity of installation description.
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Unread 07-13-2021, 01:17 PM   #4
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Welcome, Craig.

Think I'd wanna contact the manufacturer before I went forward with that. Their "Recommended material for wall surface construction" includes "Tile backer board," but I'm certainly not sure that includes foam boards.

Perhaps Laz can tell us how he is confident about that wallboard choice.

My opinion; worth price charged.
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Unread 07-13-2021, 03:25 PM   #5
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CX....Punching thru the drywall and firmly attaching to the studs should be more than adequate, or am I missing something?

I NEVER advised just an attachment to wallboard.
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Last edited by cx; 07-13-2021 at 04:11 PM.
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Unread 07-13-2021, 04:10 PM   #6
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Craig asked about attaching over Kerdi Board, Laz, not gypsum drywall. The instructions I looked at mentioned specifically "Gypsum/green board" and "Cement board."

In the instructions you read did they mention foam board?

Quote:
Originally Posted by Craig
the toilet is against an existing internal stud wall with 2 1/2" x 1 1/2" (63 x 38 mm) studs.
I think you should also ask them about the use of those undersized studs, too, Craig. I saw nothing in their literature for use of anything less than nominal 2x4 wall studs.
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Unread 07-13-2021, 04:18 PM   #7
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Gypsum, drywall, Kerdi Board....all the same to me. You need to have a solid stud BEHIND those to adhere to. THAT was my point.
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Unread 07-13-2021, 04:28 PM   #8
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While I understand that part of your point, it still doesn't address the foam board that the OP asked about. There is certainly a difference in compressive strength between gypsum drywall, CBU, and a foam board. Whether that is significant to the installation of a wall mounted toilet is something I don't know and wondered how you were so certain it didn't matter. That was my point.
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Unread 07-13-2021, 08:35 PM   #9
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I would think that, if going thru foam board may be more subject to compression than other materials, firmly embedding into wood blocking only means going deep enough for good support...not necessarily going beyond that and crushing the crap out of the Kerdi (or drywall or whatever).
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Unread 07-14-2021, 04:54 AM   #10
VapourSnow
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Thanks CX and Laz for the advice!
I will contact the manufacturer re using foam board.

Re the undersized studs, the toilet carrier will not be attached to them, as you say they don't meet the requirements.
Instead the carrier will be attached to a Unistrut frame hidden inside the wall, with the carrier screwed at the sides to a pony wall with 4 3/4" x 1 3/4" (120 x 44 mm) studs. I am not relying on the pony wall to take any of the load, only the Unistrut.
I hope I am understanding the question, or am I missing an aspect please?

Thanks
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Unread 07-14-2021, 07:08 AM   #11
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No way for me to guess very well regarding your structural support, Craig, without knowing a lot more about what you've got, but if you're content that it will properly support the toilet, that's fine with me. I'm guessing the Unistrut you're using is the same slotted steel channel we use over here for a lot of heavy electrical support work.

For the record, I've never hung a wall-mount toilet, nor even played someone on TV who's hung one.
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Unread 07-14-2021, 07:18 AM   #12
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Craig, isn't the unistrut ultimately still going to be fastened to the under sized studs?

For the masonry wall, what is it, cinder blocks?

When I installed a Geberit carrier I don't recall any provisions for securing it to a masonry wall.

The 3/4" foam board might work if your tile is a fairly large format to spread out the load but I'd still be more comfortable with drywall.
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Unread 07-14-2021, 11:05 AM   #13
VapourSnow
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Thanks CX and Dan!

The masonry wall is solid concrete masonry blocks, sorry not quite sure of the American term, we call them medium density blocks

The Geberit international planning manual covers fastening to a masonry wall and its one of the methods in the UK instructions Page 49 figure 52 of https://www.google.com/url?sa=t&rct=...lV0anLLWE0yCAr

I am waiting to hear back from Geberit re using the foam (Kerdi) board.


Yes the Unistrut is the same slotted or unslotted channel. The Unistrut frame is independent of the stud wall the carrier is against. It will be bolted to the floor joists at the bottom and at the top is connected through to Unistrut in the attic, which connects to the top plates of the side stud walls, transferring the load as compression to the external masonry walls. I've attached a drawing to try and show my thinking.

I really appreciate all the feedback, thanks
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