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Unread 05-30-2021, 07:56 AM   #31
HilltopRehab
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I’m planning out the niche, and as I consider how to land the grout lines etc I’m thinking to myself - if I build this out of Sheetrock, what treatment to the outside corners need?

I see plenty of kerdi prefab and cbu niches, but I can’t seem to find any examples of a full niche build using drywall and kerdi membrane. Is there any concern about cut edges of gypsum getting the thinset/membrane treatment - should there be outside corner beads as if it were a finished wall, or does the exposed gypsum need to be hit with an oil based primer like any paper tear repair, or should I cut and assemble such that there are only factory finished Sheetrock edges and no cut edges exposed.

Related question - can I use some of my 1/2” plywood from the underlayment scraps for the rear panel of the niche, and then apply thinset and membrane right to it? This would save the 1/2” thickness of Sheetrock.
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Unread 05-30-2021, 08:09 AM   #32
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No reason you can't fashion that niche completely from drywall, Steve, and without any concern about cut edges or factory finished edges; the paper face would absorb moisture just as readily as the gypsum core, but as you're covering it all with Kerdi, no worries.

No Sir, I don't believe Schluter condones adhering Kerdi directly to wood.
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Unread 05-30-2021, 09:49 AM   #33
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Not sure how half-inch plywood would be any better than half-inch drywall in the back of your niche, Steve, but Dan is correct, of course, that Herr Schluter does not condone applying his Kerdi to any wood substrate. But it's been done.

If you need something on the back of your niche that is thinner, how 'bout you get some quarter-inch drywall or CBU for that application?

Only thing I'd recommend for the outside corners of your niche is that you knock down the sharp edges a bit to make it easier to fold your Kerdi or KerdiBand over those corners. Raw drywall edges are not gonna make any difference in that application. See my warranty information below.

My opinion; worth price charged.
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Unread 05-30-2021, 07:35 PM   #34
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Thank you, makes sense.

A little more detail regarding the plywood idea - this wall is a 2x3 stud wall inside of a 2x6 wall shared with the hall bathroom. The main vent stack is in the wall hence the thickness.

My reason for asking is I’m unsure how I’d fasten a panel of Sheetrock to the inside edges of the studs/blocking - does it need to be screwed to something or is it common practice to simply tape and mud, or in this case thinset, that panel into position?

I have room where I could screw a thin panel of plywood to the back of the stringers before I install them, and then apply the drywall to that. I suppose “usually” niches are in 2x4 walls with wallboard on both sides, and the other side of the wall serves as some support.

I also have to consider that in the near future I intend to gut the adjacent bathroom. Luckily the double 2x3 assembly helps isolate the work of demo from a newly built tile assembly on the opposite side.
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Unread 05-30-2021, 09:14 PM   #35
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I think a photo or two might help, Steve.

At least part of the reason Schluter won't sanction the use of plywood as a backing material for Kerdi is their blanket requirement that an un-modified thinset mortar must be used with Kerdi. And that won't fly when bonding to plywood.

Were I in your situation and thought plywood would best solve my structural issue on the back of a niche, I'd simply use a modified thinset mortar meeting ANSI A118.11 to bond the Kerdi and never look back. See my warranty information below.

My opinion; worth price charged.
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Unread 06-01-2021, 05:39 PM   #36
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Attached photo shows a theoretical lower right niche corner framing. You can see the back of the adjacent wall and the 2x3 framing it’s attached to. So I don’t have anything immediately against the niche framing that could support Sheetrock while kerdi and then tile is applied. Plywood just came to mind for the added structure, maybe the modified for that spot is the way to go. Is there modified thinset in my future anyway, for the floor outside the shower? I hadn’t really thought about that or whether I *need* or want to waterproof the bathroom floor with kerdi membrane.
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Unread 06-01-2021, 10:55 PM   #37
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I would be inclined to simply glue a piece of plywood to the back of the framing and Kerdi it if you're not willing even to add a quarter-inch drywall or CBU in there.

You cannot (according to Schluter) use Kerdi to waterproof your wood framed bathroom floor. If you prefer Schluter products, you could do that with their Ditra and KerdiBand.

My opinion; worth price charged.
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Unread 06-29-2021, 11:01 AM   #38
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Update to show some of the slow progress. I glued and put a couple small screws in pocket-style to hold 1/4” plywood against the back of the niche framing. Then I glued 1/4” CBU to that for the rear of the niche.. turns out the CBU is available at this thickness in a smaller form vs Sheetrock and I don’t own a truck so that made the decision easy.

I have a sub doing the taping and mudding of the rest of the room, he went a little too far before I could remind him that the shower doesn’t need it. So he’ll have to hit that mud with primer per Schluter instructions.

I went shopping for deck mud and thinset but only to gather info… should I be looking at leaning out a 4:1 mixture? Both Mapei and laticrete mud bed premixes are at 4:1 but I read the liberry post and the guidance that 5:1 is easier. I suppose the right answer is to use the calculator and do exactly as prescribed using topping mix and play sand.
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Unread 06-29-2021, 12:05 PM   #39
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Steve, for purposes of your slope shower floor you can use any of those tile installation product manufacturers' pre-mixed mortars or mix your own. I do not recommend you use anything but a 5:1 sand/cement mix for the final mud bed in a conventional shower receptor, but you'll not be doing that.

The 5:1 sand/cement mix is easier to work with and a lot less expensive than the other mixes, but the pre-bagged stuff is convenient.

My opinion; worth price charged.
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Unread 08-01-2021, 02:16 AM   #40
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HVAC guys have done their thing re-routing and replacing the hydronic for the room, and the sheetrock is done, primed where it needs to be.

Continuing the brainstorming here, thinking about how slim to build the curb without being awkwardly small and, any feedback is welcome:

Outside the shower, the floor will be higher than inside and I'll just do the half-inch underlayment under the dry pack rather than totally replacing the subfloor planks.
With the subfloor in the shower area replaced entirely, I plan on laying the cleavage membrane and mud bed right over the new plywood.
3/4" minimum thickness at the drain and 5/8" minimum slope gets me to 1-3/8" thick mud bed at the edge of the shower.
2-3/4" minimum height of the curb from subfloor, I'm going to say that's the waterproofed curb height so that the finished curb top isn't crazy low. Planning on a 2cm quartz top for it.
--Is it crazy to consider using a 2x3 on its edge to build the curb? 1/2" sheetrock between it and Kerdi would result in a 3" height off the subfloor or 1/4" above absolute minimum.
--A curb that low would mean wall tiles ripped down to only 1-3/8" in the shower, assuming 1/4" floor tile thickness. Outside the shower, the curb wall tiles would be even smaller, about 1" if my estimate of final finish floor height is correct.

I might actually have to mock this up somehow. The top of the curb sill would be about 4" in width if I put 1/2" sheetrock on the sides of the 2x and go for 1/2" overhangs on either side. I like that width, it's the height I'm unsure of. Might look a little funny
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Unread 08-01-2021, 08:26 AM   #41
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I can't find any mention of what you intend to use for water containment over the opening to the shower, Steve. You will have a glass surround in the center of this curb or you will use a shower curtain?
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Unread 08-01-2021, 06:57 PM   #42
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The plan is to have a frameless glass surround centered on the curb, yes, with clips holding it onto the wall studs and keeping it in position on the curb as opposed to a track. The requisite swing door has swung me away from going curbless, I don’t want to worry about water running out.
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Unread 08-01-2021, 07:44 PM   #43
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The building code requirement is that the curb to be a minimum of 2" above the top of the drain. The tile industry recommendation is that the curb top be a minimum of 2" above the shower floor. One is law, the other good practice, but probably based upon the use of shower curtains. I can't prove that. The waterproofing layer of the curb top must be sloped a minimum of 1/4" per foot to the drain.

Don't know what your "clips" might be, but you absolutely do not want any mechanical fasteners penetrating your waterproof membrane on the curb top.

My opinion; worth price charged.
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Unread 08-02-2021, 11:31 AM   #44
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I’ll probably just go with the 2x4 on edge, should meet all the criteria and look good.

By clips I mean this style of attachment, I will be requiring the glass installer to only anchor the lower points in the quartz curb top and no deeper.
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Unread 09-17-2021, 09:55 AM   #45
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The subfloor & underlayment system is just about ready to be screwed down and closed up.

My earlier posts in the thread were somewhat slanted towards the idea of using Ditra outside of the shower, but at this point I'm operating under the assumption that I need to do the entire floor in a dry pack deck mud. I'm also still thinking that I'll do it myself as a rookie, but if I can find a trustworthy contractor willing to just do the deck mud and let me go from there I might be open to it. But I won't hold my breath for that, and I might do a practice pack beforehand.

Anyway, I've read a few older discussions and with this approach it seems that gluing & screwing the subfloor patches to the joists is advisable, but gluing the underlayment to the subfloor ply/planks is not. Fasten with screws, only into the subfloor material not the joists. Then goes the cleavage membrane, the stapled lath, and then the deck mud. Do I have that right?
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