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Unread 10-12-2020, 07:56 PM   #1
Bananah
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Durock set into or above deck mud?

Hi there,
I’m building a shower pan and was wondering about the pros and cons to setting Durock into the final layer of deck mud (meaning it is placed prior to doing the final mud layer) versus placing the deck mud first, letting it dry and then placing Durock above the finished level of deck mud.. I have read about doing it both ways but wasn’t sure what the consensus was on the best method to use. I plan on placing Redguard over the CBU prior to setting the tile.
Thanks so much for any insight!
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Unread 10-12-2020, 08:11 PM   #2
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Welcome, Diana.

Embedding the CBU in the top layer of deck mud is a good method of securing the bottom of the panel where no mechanical fasteners can be used. Durock is suitable for that application.

If you apply your direct bonded waterproofing membrane to the wallboard prior to placing the deck mud, I recommend you do not coat the bottom edge of the CBU, but only the face.

My opinion; worth price charged.
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Unread 10-12-2020, 08:30 PM   #3
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Thanks for the reply CX. If I paint the red guard after setting the deck mud, is it fine just to paint the cbu above the final deck mud (meaning the portion sitting in the deck mud is left unpainted)? And how far above the poly should the Durock sit along each wall? Would 1/4 inch work?
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Unread 10-12-2020, 09:04 PM   #4
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Yes and yes. I generally recommend a half-inch or so above the pan liner, but a quarter-inch will be fine. Keep in mind that the final mud bed must be a minimum of 1 1/2" thick, so a larger gap below the wallboard is not a problem.

My opinion; worth price charged.
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Unread 10-12-2020, 09:11 PM   #5
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Thanks for the thread, folks. I have a project coming up with a similar application so this is a good refresher as I've not done one of these in a while.

CX, when you say, "a good method of securing the bottom of the panel where no mechanical fasteners can be used" do you mean that no fasteners should be placed below the level of the the mud of the pan? Would this still be true if the pan was being covered with Kerdi? How far above the level of the pan would you place your first fasteners?

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Unread 10-12-2020, 09:19 PM   #6
jadnashua
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If you're using Kerdi, nothing behind it is in a wet area, so limitations on fastenes doesn't exist. In a conventional shower, no fasteners below 3" above the tope of the curb.
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Unread 10-17-2020, 06:35 PM   #7
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Everything seems to be coming along okay so far. I am at the point of placing the poly and I came across a video of somebody using plumber’s putty under the poly around the drain. I was under the impression silicone should be used. What do you all think is the best thing to use?
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Unread 10-17-2020, 07:00 PM   #8
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Hi Diana. I hope you mean the pan liner and not poly for the shower floor. Yes, we usually recommend silicone between the lower drain flange and the pan liner.
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Unread 10-17-2020, 07:05 PM   #9
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Hi Davy, yes I meant the pan liner. Sounds good, I will plan on using silicone. Last question on my mind that popped up....I was at Home Depot and saw Kerdi shower niches. Is it possible to use those in combo with cbu as long as I thinset the joints and paint over everything with red guard?
Thanks again!
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Unread 10-17-2020, 07:08 PM   #10
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I've never used those but others here have. Someone will come along to help.
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Unread 10-17-2020, 09:30 PM   #11
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I don't know how well RedGard sticks to something like the Kerdiboard used in their niche. Normally, the niche is attached by using their screws and washers, then those are covered with their KerdiBand. Now, KerdiBand would work to seal the niche to the rest of the wall. Custom might give you some idea of how well their Redgard would work over a Kerdi niche...Schluter might, but my guess is that they'd suggest using Kerdi all over.

There are other preformed niches out there. I don't know how well they would work with Redgard sealing the conversion between your wall and them, either.
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Unread 10-24-2020, 07:37 AM   #12
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Hi there,
I wanted to do a flood test for the shower pan. My question is, do I have to wait a certain amount of time after setting the pvc liner? I was thinking about the silicone around the drain and wondering if that had to set prior to a flood test. I am using an oatey drain. I’m planning on using a 2 inch oatey drain plug. It seemed difficult to get down the drain, so also wanted to see if there was a better plug to use. Thanks!
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Unread 10-24-2020, 08:04 AM   #13
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There is no wait time to flood test a traditional pan liner, Diana. The silicone under the liner at the drain, if properly installed, is just a gasket and wouldn't need to be fully cured to function. You can certainly let it cure for 24 hours before the test, but it's not really necessary. See my warranty information below.

What you really want for a plug is something the will plug the drain riser below the joint between riser and drain so it is below both that joint and the weep holes in the drain. Works easiest if you get an extension hose with it.

An inflatable plug works best. Looks like this:

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Unread 10-24-2020, 02:13 PM   #14
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Thanks CX. I will test it with an inflatable plug. I was just thinking of something else when I was going through the steps in my head. I am planning on using Redguard on the walls and it got me wondering about the curb. The pvc liner is going over 3 stacked 2x4s and then I will use Kirb perfect over that which will be filled with mud. Do I Redguard the curb as well? I know about avoiding a “moisture sandwich” on the walls but with the pvc liner being under the curb, I’m thinking I shouldn’t paint the curb with Redguard because of the same issue. Sorry for all the small detail questions, I just want to make sure I’m not missing anything.
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Unread 10-24-2020, 02:57 PM   #15
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The "small detail questions" are much better asked before the work begins rather than after you've discovered small detail problems.

The top of your rough curb should be sloped to drain before covered with the PVC liner. The liner must not have any mechanical fasteners below a height of a couple inches above the top of the rough curb except for the outside face of the curb if necessary. The curb must be finished by installing expanded metal lath and fat-mud (see Shower Construction section in our Liberry) and you do not want to apply any waterproofing membrane over that mud, nor onto the final mud bed of the shower floor.

I would strongly recommend you not use those plastic sticks in your top mud bed. First, the top mud bed is to be of a consistent of at least 1 1/2" and follow the slope of your pre-sloped liner. Second, your top mud be really doesn't want any plastic dividers to tell the mud and tile surface where to crack.

My opinion; worth price charged.
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