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Unread 06-18-2019, 08:12 PM   #1
Catmandu
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Shower with quarter round trim

I'm using quarter round tile to trim out a shower niche, and I'm now having trouble figuring out how to waterproof it. I'm using kerdi, and have applied the kerdi to the face of the wall. I held the drywall back from the face of the wall in order to create the void for the the quarter round to fit. I plan on filling the void with thinset and wrapping the kerdi across, which will result in a triangular cross section to bond the quarter round to. The problem is how to treat the corners. I can't figure out how to get the fabric to fit the corners, since they're not square. I've tried folding the kerdi every which way, but I always end up with a hole. Can I fill the void with silicone or kerdi fix, and be confident that it will result in a waterproof condition? Or is there some other way?
I've attached photos of the top and bottom corners. You can see that I've already wrapped the top edge to create the triangle. The bottom edge is flat since there will be a granite slab there. The quarter round will sit on the slab and go up both sides and across the top, with the top corners being mitered.
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Unread 06-18-2019, 11:07 PM   #2
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Welcome back, Cate.

Sometimes we have pictures that upload sideways, so I don't want to presume that yours are oriented correctly. I can't tell from the picture if we're seeing the top, sides, or bottom.

There is a template for a Kerdi niche available in our Liberry. You may be able to get it to work for your situation, since it overlaps at every junction.

I would leave enough on the outside edges of the template to wrap around those exposed corners plus an additional 2" outside for the overlap.

I'll say this for future reference: Use the preformed Kerdi Niche, which eliminates the need for all that extra waterproofing, and saves some headache. It costs a few bucks, but it's worth it.
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Unread 06-19-2019, 06:15 AM   #3
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The pictures are oriented correctly. The one on the left shows the kerdi wrapped around the top edge and the right photo shows the kerdi wrapped around the bottom.

The template and the preformed niche won't work for the same reason: the edges of the niche aren't flush with the face of the wall, in order to leave room for the quarter round tile to "wrap" around the edge. I tried using the preformed outside corner, turned inside out, but the crease is too inflexible to stretch tight across the edge. The only way I can see to get that to work would be if I could relax the crease, but don't know how to do that or if it's even possible.

So in the right photo if you imagine a strip of kerdi wrapped around the left inside wall of the niche, just like it's wrapped around the bottom, it will leave a big opening at the bottom left corner where the bottom and left side meet in an "L" shape. It's this "L" shape that's creating the problem.
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Unread 06-19-2019, 08:56 AM   #4
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I'm not sure why your quarter round tile needs a void? if your drywall met at the edge the corner round should still fit. I dont know why wont a kerdi corner work? just put lots of thinset to fill that gap in the drywall. a gap is better than if the drywall overlapped to much. your tile will not be on the kerdi but raised up 3/13" or more so imagine that and i think corner round will fit... but maybe a picture of your tiles?
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Unread 06-19-2019, 08:57 AM   #5
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Cate, I think I see what you're trying to do with the void, easier to bend Kerdi around a radius or 45┬░ angle than a sharp 90┬░corner. If I'm right the area for thinset is mostly created by the adjacent tile, no?


I've all but abandoned Kerdi fabric for things like this in favor of Kerdi Board in varying thickness. In your case perhaps you could line the niche with 3/16" K-Board.
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Unread 06-19-2019, 11:03 AM   #6
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My quarter round is bigger than what Peter shows, so it won't fit if I bring the tiles past the corner. Here is a sketch using the actual cross sections of the tiles. At the bottom, I left the void showing. At the top, I showed the kerdi fabric pulled across the corner, with the void being filled with thinset. I need to do that so the tile has something rigid to adhere to.
I'm thinking about smearing the edges of the drywall with kerdi fix before covering the remaining edges with kerdi, and filling the holes that are left afterwards with kerdi fix. The bottom of this niche will probably see quite a bit of water since it's only 15" off the floor, so I'm worried that this might not be enough.
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Unread 06-19-2019, 11:05 AM   #7
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I think the sketch didn't show up.
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Unread 06-19-2019, 12:27 PM   #8
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Cate, I'd recommend you repair/replace those corners such that they are square, but with the sharp edges eased a bit, then waterproof them and tile. The quarter-round will fit fine so long as your tiles on each face are appropriately placed.

My opinion; worth price charged.
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Unread 06-19-2019, 07:07 PM   #9
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Cate, your sketch is good. I assume your drywall is drawn as 1/2" so in relation your thinset looks to be 1/16" in scale .. draw it at 3/16" or something realistic. Does your corner round really go backd 1/2" from it's rear surface? What grout line size will you be using? draw that in to scale too.
On my doorway I made my drywall quite square but followed CX suggestion and rounded the edge some and the kerdi went on easy.
show some pictures of you tile.
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Unread 06-20-2019, 08:56 AM   #10
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Yes, the quarter round really does go back 1/2".

I drew a new sketch showing 1/8" for the thinset. The walls I already did have 3/32", but I could go heavier on this wall to get 1/8". Even if I bring the side piece of drywall flush with the face, I still have to cut off a large triangular section (shown shaded in the sketch) to let the quarter round fit and to make sure there's enough thinset behind it. I would still have the same problem in the inside corners of how to cover that odd-shaped void where 2 triangular voids meet.

But I had a new idea, shown in the right-side sketch. I would take out the existing niche, frame it 1" bigger all around, then put in durock or drywall the normal way and cover it all with kerdi using the kerdi niche template. All square corners , so no problem doing that. Then line the inside of the niche with 1/2" foam board, held back from the front 1/4"-1/2", whatever is needed to get the quarter round to fit.

1. Does anyone see a problem with putting foam board on top of kerdi?

2. I don't want to use screws to attach the foam board, so can I use silicone, kerdi fix, or thinset to attach the foam board? The sides are only about 4"x 4" and the top is about 4" x 13".

3. Since the foam board isn't technically the waterproof envelope, are the exposed cut edges of the foam board going to be a problem?
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Unread 06-20-2019, 02:32 PM   #11
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I just talked to the Schluter rep and he gave the go ahead for this idea. The kerdi board gets attached with thinset to the kerdi fabric and the exposed foam edges are not a problem.
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Unread 06-20-2019, 08:00 PM   #12
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I took down the drywall and framing for the niche and was surprised at the condition of the drywall which was covered by kerdi. I put the kerdi up 4 or 5 days ago. The drywall obviously absorbed all the moisture from the thinset. The back side of the wall is open, so it's not like it was trapping humidity in there. It isn't mushy, but is fairly friable and looks like styrofoam. Is this normal? This is the only wall in the shower that has drywall, as I ran out of Durock and had this on hand. I was going to replace it with the other half of the drywall sheet, but now I'm thinking that might not be a good idea.

The photo is of the back side of the removed drywall.
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Unread 06-21-2019, 07:26 AM   #13
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Newer drywall is kind of like formed with super secret processes that make it very light. I have noticed it to be air entrained in the manufacturing process. There will be many air bubbles, which makes it look kind of like Styrofoam inside.

It should be stiff though, the paper faces add allot of rigidity. Once you take off the paper, it will crumble easily.

If it is wet, like a damp sponge, that is not correct. I wet the drywall with a damp sponge to make the paper face dark before laying kerdi. That is normal. You do not want to like soak it though.
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Unread 06-21-2019, 09:37 AM   #14
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That is a very good observation. This new drywall has a different appearance than an old piece I had lying around from a few years ago.

While the stuff on the wall wasn't wet, the back of it looked and acted like it HAD been wet and dried out. The paper was wavy and peeled off very easily. Now I know that no one is going to be peeling off the paper on the back of the wall, but I wonder how sound it is and how well it actually holds up to the moisture in the thinset. The moisture obviously has to migrate through the back of the drywall since the kerdi prevents it getting out the front.
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Unread 06-21-2019, 10:38 AM   #15
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was this drywall brand new and installed for the kerdi? did you do it? do you know its condition before it was installed?
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