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Unread 04-17-2021, 06:36 PM   #16
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Please don't start any new threads for the same project, Steve. If you're not getting a timely response, make another post to your thread to bump it to the top of the queue for attention.

Not sure how you got overlooked the last time, but it happens. Our all-volunteer army of helpers try not to let that happen, but sometimes it does.

I hesitate to respond to question about exactly how much thickness will result from any combination of materials on accounta there is no way for me to know how accurately your measurements might be nor how your tools and techniques will affect such things as bonding mortar thickness.

In your drawing, though, the first thing that caught my eye is where you've apparently added 1/4-inch for Ditra and 1/8th-inch for bonding mortar and came up with 5/8ths-inch total thickness. Perhaps this is the "new math" we old people hear so much about? Also, your 1/4-inch allowance for Ditra is about double the actual thickness. The Ditra XL is closer to 1/4-inch thickness. it is also unlikely you'll actually have 1/8th-inch of bonding mortar under the Ditra.

Your plywood dimensions are nominal sizes and these days they will all be at least 1/32nd-inch thinner than the nominal dimension.

If it's critical to achieve a certain overall thickness, I always recommend you make up a test board using your materials and your tools and your technique and measure the final result.

My opinion; worth price charged.
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Unread 04-17-2021, 08:06 PM   #17
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Quote:
Originally Posted by CX
In your drawing, though, the first thing that caught my eye is where you've apparently added 1/4-inch for Ditra and 1/8th-inch for bonding mortar and came up with 5/8ths-inch total thickness. Perhaps this is the "new math" we old people hear so much about? Also, your 1/4-inch allowance for Ditra is about double the actual thickness. The Ditra XL is closer to 1/4-inch thickness. it is also unlikely you'll actually have 1/8th-inch of bonding mortar under the Ditra.
Ah yes, good thing it's on a white board! I also didn't note in the sketch that I want to use Ditra-heat which is the 1/4-inch thickness.

If I stick with the assumption of my longest slope line being 30 inches, and the Ditra-heat with bonding mortar will be less than 3/8-inch, then to get the required 5/8" height above the shower drain I would need to put that system on an underlayment that is an actual thickness of over 1"...

So about that deck mud.... well shoot my only real hesitation is the unclear directive regarding Ditra-heat on top of it. But I suppose that's really the decision I need to make - flattening the floor with ply and adding underlay, versus leaving most of the existing subfloor and going over it all with the deck mud. Carpentry vs. masonry. I have some comfort with the former, but the latter seems less complicated and less expensive although not without its fair share of technique.

If I were to go the deck mud route, with ditra-heat outside the shower, it seems like the curb becomes a no-brainer here so that the edge of the shower floor and the deck mud under the ditra-heat can be at different heights.

Corrected sketch attached just for future reference.
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Unread 04-18-2021, 07:50 AM   #18
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Steve, the real beauty of the deck mud is that you can make it the exact height you need and make it dead flat. I can think of nothing else I would even consider in your application.

Yeah, it's a different kind of material to work with, but there's no rocket surgery involved. And the material is dirt cheap and you can practice with it somewhere else if it'll make you more comfortable.

My opinion; worth price charged.
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Unread 04-18-2021, 12:03 PM   #19
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I do like the idea of practicing and making a test board.

Have you seen much discussion regarding Ditra-heat over deck mud? I found a post on here where someone contacted Schluter about it, the response was only that they don't know the effect of the heated ditra on the deck mud underneath it. So it's somewhat of an at-your-own-risk endeavor... part of me wonders what could go wrong and thinks of how nice it would be, the other part wonders if I should just skip the floor warming altogether.

So in this case I'd lay down felt paper as membrane, and then put 2.5lb expanded metal lath over it and staple to the subfloor , then get to packing, simple as that right?
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Unread 04-18-2021, 02:02 PM   #20
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Steve, I've got no idea why Schluter would have any reservations about installing Ditra Heat over a mortar bed. They have no problem with installing it over a concrete subfloor, which would be more dense than mortar and more likely to sink off the heat. Sorry, I'm not understanding the problem.

I'd preface that with some careful planning and marking, but yes, as simple as that.

My opinion; worth price charged.
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Unread 05-07-2021, 08:34 AM   #21
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I'm going to nix the ditra-heat after all. Not our forever home, we're going to opt to save the money and spend it elsewhere.

Has anyone else heard that Schluter is out of 1/2" Kerdi-board panels, with no ETA for US replenishment?? Granted, I was told this by Floor & Decor. I almost think that deserves it's own thread!

I still intend to use the Kerdi drain and had intended to use membrane for the receptor and board for the walls. The other peripheral components - band, corners, seals etc - seem to still be available.

I know from reading it many times on these boards that mixing manufacturers' solutions is never the best option, but have to ask - is there anything that would be a substitute for Kerdi board, or should I (and everyone else in the same boat) just be hanging regular old sheetrock and using membrane on it if I want to use Kerdi everywhere else?
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Unread 05-07-2021, 11:10 AM   #22
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I would recommend using the drywall and Kerdi membrane even were the KerdiBoard available, Steve, but that's a different discussion and has been had here many times.

As to the availability of KerdiBoard I have no knowledge. I'll see if I can locate the KerdiBoard thread in the Hangout and post the question.

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Unread 05-07-2021, 11:58 AM   #23
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I would recommend using the drywall and Kerdi membrane even were the KerdiBoard available, Steve, but that's a different discussion and has been had here many times.
Ah I see, well okay then maybe it's for the best anyway. I'll head down that path.
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Unread 05-22-2021, 09:00 PM   #24
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We've narrowed our tile selections and the plumbing is in process.

As I install the sheetrock and plan out the membrane installation, I'm reading that there are a couple options once the drain is in place. I wonder if there's a "better" option:

1. Install the sheetrock down to the bottom plate/subfloor with a small expansion gap, then install kerdi over it, then install the dry pack floor against the kerdi/drywall before applying membrane to the floor and band/corners to the perimeter of the floor.

2. Install blocking around the shower floor perimeter, then lay the deck mud floor, then install the drywall down to the deck mud with a small gap, then apply membrane from the floor up.

Seems like there's really no big advantage one way or the other, aside from being able to work on the walls and even tiling most of them before the deck mud goes down with option 1.

Oh and one other question - am I still concerned much with the grade of the plywood I need to patch the subfloor, if I assume go with the floated bonded deck mud substrate?
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Unread 05-22-2021, 09:52 PM   #25
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Steve, one of the advantages of the direct bonded waterproofing membrane method of building a shower is that you can do everything you describe in #1 without ever installing the drain 'till all the walls are installed. And that can include even tile and grout except for the bottom row of wall tile, allowing you to complete all that work without fear of damaging the floor or having to protect it.

There is no bonded method of creating a mortar bed shower floor over a wood framed floor. You use a cleavage membrane and fasten expanded metal lath over your wood subfloor before placing your sloped mortar bed.

The plywood you want is an exterior glue plywood with no face of grade lower than C.

My opinion; worth price charged.
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Unread 05-23-2021, 11:22 AM   #26
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Thanks, I'll keep going with the sheetrock then.

Quote:
Originally Posted by CX
There is no bonded method of creating a mortar bed shower floor over a wood framed floor. You use a cleavage membrane and fasten expanded metal lath over your wood subfloor before placing your sloped mortar bed.
Ah right, I can't help but think of the fastened lath as "bonding" the mortar but I understand there's a difference.

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The plywood you want is an exterior glue plywood with no face of grade lower than C.
As for the thickness, my original subfloor planks are at actual 3/4" thickness. I'm supposing that another beauty of the deck mud route is that I can forgive a 1/32" difference in thickness with today's nominally dimensioned products, is that a safe assumption?
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Unread 05-23-2021, 12:36 PM   #27
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Yes sir, you are correct
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Unread 05-23-2021, 06:08 PM   #28
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You understand need a layer of at least nominal half-inch plywood over the board subfloor before your mud bed, yes?

Unless, of course, you want to make a reinforced mud bed, which would be a minimum of 1 1/4" thick and have welded wire mesh in the vertical center in lieu of the expanded metal mesh at the bottom.

My opinion; worth price charged.
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Unread 05-24-2021, 06:20 AM   #29
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You understand need a layer of at least nominal half-inch plywood over the board subfloor before your mud bed, yes?
Shoot, no I hadn't realized that, I got the impression the subfloor reinforcement was needed for the Ditra route.

Does that go for areas where I replace the board subfloor altogether? I suppose it does... so I need to patch the board subfloor where I've opened it up (shower, toilet), and then get nominal half-inch ply over the whole floor, is that right?

Should I be okay with the patched subfloor being 1/16" thinner than the original, with the 1/2" nominal ply over top it seems that should be fine.. a little wavy but therein lies the beauty of the deck mud floor.
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Unread 05-24-2021, 09:21 AM   #30
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If you replace the entire board subfloor with plywood, you could do your mortar bed over metal lath over cleavage membrane directly over that, Steve. The idea of the half-inch plywood is to separate your tile substrate from the sawn board subfloor. The same mortar bed over an appropriate single-layer plywood subfloor is also acceptable.

My opinion; worth price charged.
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