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Unread 10-06-2020, 06:34 AM   #1
vlocka
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DensShield with Kerdi membrane and painted ceiling

so I'm building a 3X6 foot stand in tiled shower with curb. The shower is already boarded with densheild and were doing a drypac shower floor with tile. I want to waterproof the walls with Kerdi membrane. The ceiling won't be tiled so i have to put Sto-Flexyl on it and then coat it with sto flexyl sealer to waterproof it for paint.

My question is on the ceiling joints how would I waterproof the corners where the kerdi membrane meets the ceiling?

Also how would I waterproof the bottom of the walls where it meets the drypac? Also should I just kerdi membrane the whole curb. (Curb is just 2x4 stacked covered in densheild.
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Unread 10-06-2020, 06:39 AM   #2
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Here are some photos
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Unread 10-06-2020, 08:21 AM   #3
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Welcome, V.

Are you doing this work yourself or are you paying someone to do it?

Just at a glance I've gotta point out that the current construction is fatally flawed by the installation of the DensShield on the curb using mechanical fasteners that penetrate the waterproof liner. There is no acceptable method of using a CBU or similar board on the curb of a traditional shower receptor.

And the manufacturer of the DensShield - Georgia Pacific - does not indicate the use of their product in that application, nor the installation of your walls down into the top mud bed of your shower receptor.

My next question would be whether there is a proper pre-slope under the liner on the shower floor?

I'd recommend you reconsider moving forward with what you've currently got there.

I'm not familiar with your Sto Flexyl product, but wonder why you feel you need it on your shower ceiling. How high is the ceiling above the shower floor?

My opinion; worth price charged.
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Unread 10-06-2020, 08:55 AM   #4
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Im paying some one to do the tiles, but i am doing the drywall and waterproofing.
from the ceiling to the shower floor is 6ft.

I know i shouldn't have drilled into the liner but how else do i attach Backboard onto of the curb?

what is the proper way to make a curb waterproof?

There is no pre-slope under the liner. I have been contacting many plumbing companies here in Canada considering this. About 50% say on new builds they don't use a preslope. Just a dry pac slope above the liner which i know isn't correct.

I feel i need to waterproof the ceiling because its just densheild and i won't be tiling the ceiling. So the only way i could go about painting it would be putting sto-flexyl coat and then they said i could paint over it.
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Unread 10-06-2020, 09:31 AM   #5
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It'll help if you'll put that geographic location into your User Profile so it appears in each post to aid in answering some types of questions.

Quote:
Originally Posted by V
I know i shouldn't have drilled into the liner but how else do i attach Backboard onto of the curb?
Quote:
Originally Posted by CX
There is no acceptable method of using a CBU or similar board on the curb of a traditional shower receptor.
You don't. That's what I was pointing out above. You cannot do that.

If you'll visit our Liberry and go to the Shower Construction thread there you'll find an article on how to properly prepare a traditional shower curb using metal lath and "fat-mud."

The shower pan liner is part of the shower plumbing and our plumbing code requires that it be sloped to drain, but the ceramic tile industry down here also requires the liner under the final mud bed to be sloped and the final mud bed to be a uniform thickness of at least 1 1/2-inches to follow the slope of the sloped liner. I think TTMAC up there has a similar requirement.

That is a very low ceiling and it wouldn't hurt to have it waterproofed. Properly installed, I think you'll find that the DensShield is adequate in that application. The added waterproofing won't hurt, of course.

I don't think your DensShield installation on the walls will meet anybody's installation instructions in your application, though.

My opinion; worth price charged.
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Unread 10-06-2020, 09:42 AM   #6
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"I don't think your DensShield installation on the walls will meet anybody's installation instructions in your application, though."

What do you mean by this?
It wasn't installed right?

Also is it ok if i put kerdi membrane over the densheild walls for waterproofing or should i just to the mesh tape with mapei MPG stuff.

Im also located int toronto, ontario canada
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Unread 10-06-2020, 12:34 PM   #7
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In the USA, plumbing code requires that the waterproofing in a shower pan be sloped to the drain. That is NOT the tile...it is the liner. It also calls out for no penetrations to the pan below 3" ABOVE the top of the curb, so that means NO screws into anything there.

There are two classes of cement board...Denseshield is not a cement board. It is essentially, a water resistant drywall. In the USA, there are only two approved products you can use with drywall in a shower, and neither one involves the pan material you have. While it can be used on the shower walls, it cannot be embedded into the pan and that includes the curb.

Normally, anything above the height of the shower head in a shower is not considered a wet zone, although it could get splashed...it won't typically see much water and a quality paint usually suffices to protect things. Doesn't hurt to improve on that, especially if the ceiling is low.

Kerdi membrane is designed as a system...trying to combine it with a conventional pan liner is asking for problems. When used as designed, the entire shower beneath the tile is a unified, waterproof container. It also requires a specific drain that you do not have. To use that, you'd have to replace the drain, tear out the liner, and then cover what you have (after making your sloped bed) with Kerdi. Because Kerdi waterproofs the entire surface, the Denseshield isn't an issue other than requiring a specific type of mortar to attach the membrane.

FWIW, one study found that 75-80% of tiled showers were not built to industry standards. That doesn't mean they all failed, but most of them do, eventually...some sooner than others.
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Unread 10-06-2020, 01:31 PM   #8
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Kerdi over Densshield is a big problem. You're putting mortar between two impervious surfaces, so it won't dry, at least for a very long time.
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Unread 10-06-2020, 03:09 PM   #9
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Ok so only 1 of my questions was answered so far.

So instead of telling me whats wrong which i got now.
Im asking what can i do.

Here in cananda you are supposed to put a pre slope but most new builds don't, so i will go with that the plumber has been doing.
I will be buttering the curb and waterproofing it.

My curb is 8 inch so the screws on the side are above the called for 3 inch from above.
Just the ones on top are wrong.


SO again for my densheild. Instead of waterproofing my walls with kerdi membrane. How should i go about waterproofing my walls?

i just figured i could throw the membrane on to waterproof it.
I read a thread on here that CX even said you could put Kerdi Membrane on densheild as a waterproofing instead of aqua guard.


So how would i go about waterproofing my joints and screws on densheild ?
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Unread 10-06-2020, 04:19 PM   #10
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The TCNA handbook only requires a moisture barrier on the walls of a shower. Your current panels are a moisture barrier, but you'd still have to follow the manufacturer's installation instructions (have you read them?). IT does not require them to be waterproof. Only the pan must be waterproof. When paying someone to install this sort of thing, it is an implied contract that the work is done to industry standards which also means, following the manufacturer's instructions of the products involved. Failing any of that breaks the implied contract, regardless of what it might say in yours with the contractor.

If you attached Kerdi with a compatible thinset, it wouldn't matter that you have two impervious layers, as those will cure without drying properly. I do not think that Schluter lists that material as a suitable substrate, but you could call them if you wanted to verify. They have certifications that list only certain backers, which includes cement boards, plain drywall, etc. But, to get that certification, it's an all or nothing...you'd need to use their drain and put Kerdi on the walls, floor, and curb, too.
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Unread 10-06-2020, 04:21 PM   #11
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V, I know we're not telling you what you want to hear, but we're telling you what you need to know. What you've currently got is unacceptable, not just from a tile industry standard perspective, but as a practical mater.

You've got penetrations in your receptor waterproofing membrane that are not acceptable at all. The only way you can correct that is to either replace the membrane or remove the Denshield and patch the holes. Given that you've got no pre-slope, starting over with a proper pre-slope and a new membrane would be my recommendation. No sense building a new shower that already has built-in leaks. Will what you've got fail before Christmas? Probably not, but it will most certainly fail prematurely.

Not sure we're on the same page with the fasteners you've got. The requirement is that your pan liner rise a minimum of three inches above your rough curb and you cannot have any fasteners below the top inch of that. There are some arguments in the reading of the requirement, but no one argues that you can have a penetration lower than two inches above the level of your rough curb top. That includes at the bottom of your wallboards and anywhere on the curb except the outside face. Not permitted. That's here in the USofA, but I expect your codes and TTMAC have similar requirements.

While your DensShield has a face that the manufacturer says is "moisture resistant," I believe, it is still a gypsum board and the edges of it cannot be exposed to moisture in your shower. It's very tricky to do a walk-in shower with that product and comply with the manufacturer's instructions.

My recommendation would be that you stop where you are and re-assess your options. If you want to do a traditional receptor, I suggest you remove at least the bottom panel of your wallboard and all the material from your curb. Then remove and discard the liner, create a proper pre-slope, and install a new liner with appropriate dam corners at the ends of your curb.

Then install an appropriate CBU with no fasteners below the level prescribed by your plumbing code, tile industry standards, and product manufacturer's recommendations. Make a curb using metal lath bent over your curb liner over your sloped curb top and encased in fat-mud to the size and shape you desire.

You can then waterproof your walls (you can use Kerdi if you want), place your final mud bed, and tile your shower.

My opinion; worth price charged.
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Unread 10-07-2020, 05:46 AM   #12
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If it were me, I'd cut that liner and drain outta there, and just use the entire Schluter Shower System. Whether you use a prefab pan, or drypack is up to you. 6' seems like an awfully low ceiling to me.

https://www.schluter.com/schluter-us...er-System/c/SS
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Unread 10-07-2020, 07:14 AM   #13
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If you choose to ignore everyone's input about a "do over" is up to you.
I would use the liquid Mapei on the board instead of a sheet membrane for the reason Kman
mentioned, the thin set between the coating of the DensShield and Kerdi would take a long time to set up unless you used a rapid set. Coat the screw heads and seams with Liquid and hope for the best.
As a manufacturer of Shower Pan the slope is required UNDER the liner!

I can show you videos of people doing all sorts of stuff wrong ,like cleaning a loaded gun!
Had someone send me a video of someone nailing their shower pan to the floor..whats your point?
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Unread 10-07-2020, 07:53 AM   #14
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1. Thanks for all the help. So your saying even if I mapei the curb with aquaguard then mud it then aqua guard again that it will still leak?

2. Also I can show you a video where the new builds have no pre-slope. I know its not the right way but builders have done it like this before.

https://youtu.be/pmz2nsWV2Zo


3. Also what is the proper way to waterproof densheild. I still haven't gotten an answer? Hahha

My shower height is 8 feet also. Sorry for typo.
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Unread 10-07-2020, 08:02 AM   #15
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Other then the fasteners and joints you do not have to waterproof DensShield when it is installed correctly it has a "waterproof/resistant" coating on it. That means the bottom of the board needs to be 1/4" above the floor, and you don't use it as a curb! amongst other things....... Download the written direction for the products you are using and follow them.
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