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Unread 03-04-2022, 11:16 AM   #1
Jeff O
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Kerdi Membrane shower with prefab pan, project questions

Hi,

I've built two Kerdi membrane showers many years ago and I'm about to start another. I have a copy of John's Kerdi book on a computer somewhere, but no idea where it is at this point. Perhaps I'll buy another copy but in the meantime a few questions.

The first question concerns the flange connection.

This is an alcove installation with a prefab solid surface pan. The pan has a nice flange on three sides. I wanted to brush up on the install instructions so I watched a Kerdi video which showed the flange installed flush with the drywall backer. This makes sense, but I don't recall doing it this way in the past. In order to install my pan flush would require modification to the framing and potentially moving the toilet in the process. Panic! I then consulted the Kerdi System installation handbook and the requirements say:

"Solid backing panels...shall be either installed flush with the tub flange OR over the tub flange leaving a minimum space of 1/4" (6mm) between the board and the tub deck."

Based on this statement, I presume it is OK for the drywall backer to stand proud of the flange, at 1/4" above it. (the drywall should not make contact and overlap the flange, right?)

I recall filling the gap/flange with kerdifix while applying the kerdiband "collar" around the entire flange and bottom of the drywall.

Am I interpreting this correctly?

Second question is regarding thinset mortar for the membrane. I've used Versabond in the past based on John's recommendation. I realize it does not meet the Schluter spec, but a quick search on these forums seem to reveal that Versabond is still considered a good pookey option. Schulter's own brand of mortar was not available when I did my previous projects but I don't plan to use it this time either.

Is Versabond still a good choice for adhering the membrane to drywall and tile to kerdi?

Additional followup questions very likely.

This forum is a lifesaver that I've used for years. Thanks in advance for the advice.

Jeff
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Unread 03-04-2022, 03:30 PM   #2
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Welcome back, Jeff.

Quote:
Originally Posted by Jeff
"Solid backing panels...shall be either installed flush with the tub flange OR over the tub flange leaving a minimum space of 1/4" (6mm) between the board and the tub deck."

Based on this statement, I presume it is OK for the drywall backer to stand proud of the flange, at 1/4" above it. (the drywall should not make contact and overlap the flange, right?)
I think you're missing the big "OR" in that quote, Jeff.

You can stop your drywall above the top of the receptor's tiling flange and have the face of it flush with, or a bit proud of, the face of the tiling flange.

OR you can have your wallboard extend down past the face of the tiling flange on the drain side and stop 1/4" above the horizontal surface of the receptor. I would personally not recommend you do this if you're using gypsum drywall as your backing material, but would always favor this method if using fat mud or CBU.

Stopping the drywall above the flange works well using Schluter's method of bonding the Kerdi membrane to both the tiling flange (using Kerdi Fix) and the drywall (using thinset mortar). If using this method I would further recommend you give the membrane a little wedgie into the very small gap above the flange to allow for movement accommodation.

My opinion; worth price charged.
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Unread 03-04-2022, 08:20 PM   #3
Jeff O
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Hi CX,

Thank you for the response. I think I mis-worded the quote a bit, but I do understand the difference in the big OR that you point out.

I will stop the drywall backer 1/4" above the flange and it will be slightly proud of the flange. Good suggestion about the wedgie.

Regarding the Kerdiband "collar" do you suggest one continuous band around the shower pan or cut at each corner? My recollection is that multiple layers of kerdi membrane/band can be a problem especially in corners.

Thanks again. Jeff
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Unread 03-04-2022, 09:09 PM   #4
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Jeff, you may be confusing the terms "tub deck" and "tub flange". In the drawing below, you'll see how you should install sheetrock right down to the tub flange, but not in front of it. Your Kerdi collar will attach to the face of the flange and to the face of the wall board.

Name:  tub-flange-cross-section.jpg
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You could also install a cement or foam board (or something similar, not sheetrock) in front of the flange, as long as it stays at least 1/4" above the tub deck. I would never recommend installing the board down on the tub deck.

So another important question: does your shower receptor have a flange all the way around and to the floor, like this one:

Name:  good flange.jpeg
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....or does the flange stop somewhere near the front corners like this one, like it was made by someone who hates tile installers? (They're both tubs, but you get the idea.)

Name:  bad flange.jpg
Views: 284
Size:  37.6 KB
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Unread 03-05-2022, 12:33 AM   #5
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Hi Kevin,

It is indeed the flange that I am referring to. The alcove rough framing is 48" wide--same as the shower pan. The flanges are about 1/4" thick and sit tight to the framing; the drywall is obviously thicker at 1/2" so it sits proud of the flange. Basically the same as the image you posted, but the flange and drywall ends are not flush--the thicker drywall is proud so there is a 1/4" space below the drywall (and ultimately behind the bottom row of tile) . The drywall backer and flange don't actually make contact with each other correct? The image you posted seems to show the two in direct contact. I can do either has I haven't installed the drywall yet.

I copied and edited your image. The red area is a void. The subsequent tile install will then "hang down" to the shower deck covering the void.

The prefab pan is a shower rather than a tub. The flange goes all the way to the edges.
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Unread 03-05-2022, 02:41 AM   #6
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Quote:
Originally Posted by Jeff
The flange goes all the way to the edges
So does that mean it turns the corner and goes to the floor? I'm asking because a common area that tubs and showers let water out is at those two corners. If there's a flange there, you can continue the waterproofing just like the rest of the receptor.

If there is no flange, water often runs out and causes damage to the wall in that area.

As far as the wall board touching the flange, I would not let the weight of the board rest on top of the flange and screw it into place. That doesn't allow for any expansion.
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Unread 03-05-2022, 12:02 PM   #7
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Kevin,

The flange goes all the way to the front edge of the threshold, but does not continue down the front of the pan to the floor. I don't recall seeing any that were designed that way--as you said, probably because the designers hate tile setters!

The glass door I've selected is positioned to set back to the inside edge of the threshold so it overlaps the flange by a couple inches. I'm hoping this will minimize potential splashing/leaks onto the floor.

Thanks again for the info.
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Unread 03-05-2022, 12:17 PM   #8
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A couple of followup questions:

1. In the original post I asked about using Versabond to both adhere the Kerdi to the drywall and to set the tile. I realize it doesn't meet Schluter spec but is it still considered to be a good choice?

2. I've been informed by my wife that a niche is non-negotiable and it's always good to keep the boss happy, so a niche it is. Years ago I did build one using kerdi and kerdiband but the buildup in the corners always bothered me. I was using larger tiles on that job and it wasn't much of a problem but I don't look forward to doing it again. Aside from the price, the prefab Schluter niches appear to be a better choice. I wish they were available in more sizes as even the largest one is much smaller than what she has in mind. Any thoughts on building a custom size vs. the prefab Schluter?

Edit: I may have answered question 2 on my own. I just re-read the Kerdi niche info. Apparently the little shelf on the larger sizes is removable. If so, then one of the larger sizes will be just fine. Also, I see that it can be imbedded under the membrane which would eliminate the use of kerdiband (and associated buildup). Seems like a no brainer to use the prefab niche.
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Unread 03-05-2022, 12:56 PM   #9
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1. Considered by whom, Jeff? I'd consider it a good choice, 'specially because it's the only brand of materials conveniently available to me and I know it works just fine in that application.

Does that count?
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Unread 03-05-2022, 07:41 PM   #10
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Yes indeed, that counts! I'd consider a recommendation from CX to by as good as it gets. Yes I know the warranty info and price charged etc.

As an aside, I can see from the "similar threads" suggestions at the bottom of my thread that several of my questions have been answered countless times. I'm not lazy-I did do a search prior to posting, but I guess I'm not very good at phrasing the questions. I'm sure the regular pros on here are tired of answering the same questions over and over. The advice is invaluable. Thank you.
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Unread 03-05-2022, 07:54 PM   #11
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Quote:
Originally Posted by JeffO
I wish they were available in more sizes as even the largest one is much smaller than what she has in mind. Any thoughts on building a custom size vs. the prefab Schluter?
Jeff, you also have the option of making any size niche you want using Kerdi Board and Kerdi Fix. Or you can make two pre-fab niches into one larger one.

Schluter has a video on that topic somewhere on YouTube. BTW, I'm just a few cities north of ya.
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Unread 03-05-2022, 08:10 PM   #12
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Quote:
Originally Posted by Jeff
I'm sure the regular pros on here are tired of answering the same questions over and over.
If they were, some of'em woulda had to quit twenty years ago, jeff. Just goes with the territory as we have it structured. Don't worry about it.
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Unread 03-05-2022, 09:17 PM   #13
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Good idea John. I think the 12 x 20 niche will work especially since the shelf can be removed. You north of Sonoma County? I should update my profile. Still have a property in Marin, but currently living in the PNW.


cx, your name pops up all over these forums and I always learn something and often get a chuckle too. . 94K posts and counting. I'm not sure I've drawn than many breaths in my lifetime. Cheers!
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Unread 03-06-2022, 11:50 AM   #14
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I'm replacing the drywall on the ceiling in the shower alcove and adding new drywall to the walls as well.

I plan to run Kerdi membrane all the way up the walls to the ceiling.

Is there any reason to tape the seams in the alcove ceiling/wall intersection? I'm thinking I could just run a thin bead of caulk in the joint-if there is any gap.

I know it's better to not have any joint compound to interfere with the membrane installation and won't tape any part of the walls in the shower area.

Thanks in advance.
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Unread 03-06-2022, 12:53 PM   #15
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Jeff, that joint is required by code in some compliance jurisdictions to be filled and taped. And doing so should not interfere with your Kerdi installation if you limit it to level 1, which is simply filling and taping, and your Kerdi will stop on one side of the joint. Up to you how you wanna treat it.

My opinion; worth price charged.
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