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Unread 02-07-2021, 04:12 PM   #1
Brian Bower
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Question regarding Kerdi Drain Install

Hi All, new member here. My name is Brian seand I am doing a repair/renovation for a shower that had a significant dry rot issue. Anyway - enough backstory...

I have decided to do the new water management system for the shower and going with a kerdi drain. All the info I have seen on the install indicates setting the drain flange in mortar base. Has anyone ever had any issues with the kerdi flange not bonding into the mortar base? I put mine in yesterday and this morning it when I tap in the flange it has a hollow sound on one side like it is not bonded to the mortar bed. I assume this is not good for longevity of the shower, and wonder should I remove the whole flange and reset in silicone or kerdi fix or should I simply pump silicone kerdi or something else into the kerdi design that runs around the perimeter of the flange.

Thanks in advance -
Brian
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Unread 02-07-2021, 05:48 PM   #2
jadnashua
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Basic deck mud won't bond well. What they told us in class was to mix up a small batch of the deck mud and put some additional cement in it to use underneath the flange.

Is the drain glued in, or were you going to be making that connection later from below? If you have access from below, you can probably get the drain out, maybe spread some thinset, then re-set the drain.

Someone may have some better choices, and on Monday, you should consider calling Schluter's help line.

You don't want any movement in the drain when you're done.
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Unread 02-07-2021, 06:09 PM   #3
cx
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Welcome, Brian.

The Kerdi drain was not designed to bond to anything on the bottom side. Some newer bonding flange drains were made with the bottom of the flange the same as the top and designed to actually have thinset mortar applied to the bottom before the drypack mortar was packed under the flange. Schluter may have done that with their newer drains, but I've no information to that effect.

That said, I never worry about bonding the bottom of a bonding flange drain to anything. As Jim pointed out, I generally put deck mud in a gallon can, toss in exactly one handful of dry Portland cement or thinset mortar, whichever is closest, and mix that up with just a tad extra water and pack it under the flange.

So long as the flange is properly supported, it will stay in place just fine once the thinset mortar for the waterproof membrane is troweled into the holes around the edge and the membrane bonded with the top of the flange.

I've never even considered whether it was bonded below the flange or not. Without being able to see and touch yours, I can't tell if you have a problem. Not sure what we're looking at in the photo. What's the white material?

My opinion; worth price charged.
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Unread 02-07-2021, 07:11 PM   #4
Lazarus
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Whenever I'm setting a Kerdi flange, I like to mix up some Mason Mix or "Brick Morter" and force that under the flange. It sets up nicely (like fat mud) and is rock hard within an hour or so. To this, a slurry of thinset on the edges and the floor for the mud to adhere and the base is bulletproof......
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Unread 02-07-2021, 10:13 PM   #5
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What did you put under the flange? It looks different than the deck mud around it.
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Unread 02-07-2021, 10:27 PM   #6
Brian Bower
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Thanks for the quick feedback gents -

I have not connected the waste line yet, was planning on doing that afterward.(subfloor situation) So, because I did not want the flange moving around while screeding, I set it in a quick setting mason's(brick) mortar so it would harden off quickly.

I gathered from the mix of comments that it might be ok with the thin set that will go down for the waterproofing membrane, but can hold off for a day or so in case subsequent feedback indicates otherwise.

Thanks Again,
Brian
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Unread 02-07-2021, 11:20 PM   #7
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Ok, so as long as the mortar under the drain and the deck mud were done at about the same time so they could bond to each other, that should be fine. You don't want one drying independently of the other, giving you a cold joint there.

Approximately how much of the drain is unsupported? I doubt a thumb-sized spot will cause a problem, but something big enough to flex under the weight of someone stepping on could be a problem.
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Unread 02-08-2021, 12:07 PM   #8
Brian Bower
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Thanks Kevin - I wouldn’t characterize the area in question unsupported, it is just that tapping around the perimeter, I hear a sound on about half of the diameter that seems like it is not bonded to the mortar beneath it. When I tap on the outer edge of the plastic flange, it bounces the slightest bit. I could see where laying in the thin set could remediate that if the thin set bonds completely with the dried mortar, but yeah, I don’t want any movement. If I need to I am more than ready to pull that flange out and reset it.
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Unread 02-08-2021, 12:12 PM   #9
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I probably would if I were you. You may find some high spots that you can knock down and have a smoother surface. Spread some mortar over it and push the drain into the mortar, making sure the flange is not higher than the surrounding mud. Make sure the flange is level in every direction, wipe off the excess and you're finished.
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Unread 02-08-2021, 06:20 PM   #10
Brian Bower
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Keven, that makes sense. I was thinking about it a bit after looking again at the photo. I noticed that the pattern of the dried masons mortar give the hint that something moved. The high spots there seem out of alignment with the holes in the flange rim. I recall having to get some additional mortar mixed to finish the job and that it was still a little thin when I was troweling it in. I think is just sloughed out a bit and I was too preoccupied with setting the deck mud that I didn’t notice.

Looks like I am pulling and resetting it before continuing. Thanks again for helping me think it through
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