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Unread 01-06-2021, 08:20 PM   #1
Nullsignature
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Thinset selection

I'm installing a tiled shower and want to make sure I get the thinset right. The base will be a KBRS tile basin and I'll be using 1/2" redguard coated cement backerboard for the walls.

For mortaring the tile basin to the floor, KBRS has this to say:
Quote:
Any quality "polymer modified" thin-set will do just fine. [...] The thin-set must meet or exceed ANSI A118.4 and ANSI Al18.11 requirements when mixed with water.
They also indicate to use a 3/4" U notched trowel.

For the shower floor I have a marble hex mosaic and the walls are a ceramic 4x12 subway (I'm using a 4x4 bullnose version for the niches).

The thinset I'm looking at is Mapei's basic ceramic tile mortar (it's not letting me link it in the post? Lowe's item # 3743805). Will it be OK for these applications? I thought a LFT type thinset for the shower basin might be more appropriate, but the manufacture doesn't call one out so figured it might be unnecessary. Also, there is one store in town that carries UltraFlex 1 if that would be more worthwhile to use? I have access to a Lowe's, Home Depot, and Floor and Decor so anything they carry is available to me.
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Last edited by Nullsignature; 01-06-2021 at 08:25 PM.
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Unread 01-06-2021, 08:35 PM   #2
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Mapei Ceramic Tile mortar is (somebody can correct me if I'm wrong) essentially the same thing as Ultraflex 1. Mapei just gives it a unique name for retail at Lowes. Both meet the A118.4 spec so would be fine.

IMO the cost delta between those "basic" mortars and the next step up ones ones (Ultraflex 2 or I think the Lowes version is called Porcelain Tile Mortar?) is quite small, a couple bucks per bag, than I always go with the higher spec one.

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Unread 01-06-2021, 08:37 PM   #3
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Welcome to the forum.

Someone may correct me on this, but I think that product at Lowe's is the same as Ultraflex 1. It's just bagged differently for sale at Lowe's.

But I think either will be fine for what you're doing.
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Unread 01-06-2021, 08:39 PM   #4
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I couldn't find UltraFlex 2 here so I assumed nobody stocked it, but I just did some quick Googling and it looks like you're right. Thanks for the insight!
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Unread 01-07-2021, 12:44 PM   #5
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How to install backerboard in the back of niche

I am doing a recessed niche and the wall on the other side of the niche is drywalled. I'm wondering, what is the best way to install backerboard against this drywall?

I've seen methods where a piece of backerboard is thinsetted against the back of the drywall. I don't want to do this, because then the shower niche is structurally dependent on the drywall of another room. That doesn't seem like a good design practice. I've also seen where people waterproof and tile directly on the back of the drywall. Same concern.

From the perspective of the 'other room,' I'm thinking about cutting a 1/2" notch into the edge of the studs that is the size of the niche. I would then screw the backboard into notches and place drywall over it. Basically, the backerboard would be attached to the studs from the back instead of the front.

Thoughts? Prefabbed niches won't work due to some limitations, it has to be custom.
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Unread 01-07-2021, 01:26 PM   #6
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I've tiled to the back of the drywall quite a bit. After I converted to Kerdi showers years ago I would attach the Kerdi to the back of the drywall. I have never cemented backerboard to the inside of a niche because I didn't want to give up the space.
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Unread 01-07-2021, 01:33 PM   #7
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Welcome, W.

I've combined your two threads for this project here so folks can see what you're working on and what's been previously asked and answered. A moderator can give it a more generic title any time you'd like to suggest one.

Not sure just what the concern is with the drywall on the back of your niche and I don't see that going to the trouble of cutting out the drywall in the other room, rabbeting out groves in the studs, fastening your CBU there, then patching the drywall really buys you much of anything. What am I missing?

Were it mine and I wanted to pookey the CBU piece to the back of that drywall, I'd do so and never look back. The greatest danger for that method is someone wanting to fasten something to the opposite wall. And your method would not provide any more protection from that.

My opinion; worth price charged.
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Unread 01-07-2021, 01:52 PM   #8
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The concern is that being structurally dependent on the drywall of the other room means that any remodeling or work in that room may require the niche to be retiled. We are running into this issue with an existing bathroom that has already been remodeled. In order to complete work unrelated to the bathroom, we will likely affect the tile in the niche.

It's a future proofing exercise, nothing more.
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Unread 01-07-2021, 01:59 PM   #9
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why can't you put some studs to frame out the niche and tie them to the existing studs??? What am I missing???
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Unread 01-07-2021, 02:04 PM   #10
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That's what I'm doing, the concern is the back of the niche, not the framing
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Unread 01-07-2021, 07:56 PM   #11
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GoBoard transition to drywall

What's the recommended way to transition from GoBoard to drywall? Will the polyurethane caulk + waterproofing membrane be sufficient (like for every other GoBoardoard joint), or does it need to be thinsetted + waterproofed? I plan on putting the transition under tile. I also plan on using greenboard, if that makes a difference.
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Unread 01-07-2021, 11:07 PM   #12
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If the surface on the back of the niche does not firmly meet the drywall on the room behind it, you'll want to add a backer behind the niche so that there is no flexing or bowing when pushed on. A piece of drywall or tile generally works...
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Unread 01-07-2021, 11:36 PM   #13
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Use a preformed niche, like a Recess-it niche. It's metal, and stands on its own. You lose almost no depth of the wall cavity.
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Unread 01-08-2021, 08:47 AM   #14
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I use this one if I don't custom build them

https://www.noblecompanyonlinestore....ar-noble-niche
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Unread 01-16-2021, 12:44 PM   #15
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Schluter edge size selection for tile

I am trying to select Schluter edge trim for my 4x12" subway tile that is 5/16" thick. I'm worried that a 5/16" Schluter edge trim may not flush when the thinset thickness is taken into account. Would a 3/8" be better? Or even 7/16"? I can't find helpful sizing guidelines from Schluter. 3/8" is in stock locally but I would have to special order 7/16".
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