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Old 03-25-2018, 09:51 PM   #1
milnerpt
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PT Dan's Kerdi Shower

Been lurking this forum for 2 years as I have finished out my basement. I work healthcare, but have an inquiring mind, and have done much of my own work - learning different trades in the process. I knew early on, I wanted to have a curbless shower with a non-traditional waterproofing (ie - membrane of sorts)

The problem is, several subcontractors have put some items in before I really had a chance to research each aspect and product, which leaves me with a variety of products and I am trying to figure out how to make them work together. Searching the forums I have learned may different aspects of each one, but just really cant put all of the pieces together given my circumstances.

Background:
My finished basement was created in a 9 foot crawl space under the home. I have 5" of pea gravel (22 tons shoveled my moi), vapor barrier, 2" of XPS rigid foam, PEX hydronic tubing, and 4" of concrete poured on top. I originally boxed out the area for the shower (so no concrete was on it) before the pour. Obviously had my plumbing installed in the drain rock before the insulation and concrete.

First problem: plumber convinced me he has done many a kerdi-showers and would place a drain and set the slope to the shower floor. He stated he used a cheaper drain type, not the standard kerdi ones, and they work fine in his application. He installed a drain (not kerdi, but one with 3 pieces, bolts on the drain out, an intermediary piece, and a threaded drain), and instead of using dry pack, actually mixed up concrete, sloped it, and set the drain in it. It does appear to be properly sloped. He indicated when I ultimately applied something to the surface, use a "bonding agent"? as if the concrete had cured too long, something may not stick to the surface (like using unmodified thinset of kerdi?)

Second problem: Drywaller said he had just the stuff for the shower. I really didnt go into details with him, as I was planning on installing a surface membrane over it anyhow. He used a blueboard material in the bathroom, but diamondback in the actual shower area. I didnt even know about the product until I looked on the boards more about densshield and diamondback (which appear similar). He did appear to install it according to manufacturers instructions - no seams are taped, screw penetrations are exposed. They did seem to leave about 1/2" gap on the bottom between the floor and bottom of board. One area its more like an inch.

I dont particularly trust the diamondback, and cost of liquid membranes is substantially cheap enough I can just paint the surface with appropriate thickness/coats. Diamondback manufacturers seem OK with this. However

What should I do about the larger gaps at the bottom of the shower (1/2-1"). If I just paint the floor with liquid membrane, how do I finish the interface with the drain I have set in the poured pan? I figure with the drain I have, it would allow for moisture to seep through into the concrete poured shower pain.

Luckily, moisture into this 'pan' shouldnt be a big problem, as that concrete being damp really shouldnt be a huge source of rot, any more than moisture on the rest of the concrete floor would cause rot.

Any problems putting scraps under those gaps, and painting the whole thing with a liquid membrane, set the drain, and be done with it?

(then Ill figure out how to tile, which thinset to use, etc etc)
Pictures available on request
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Old 03-25-2018, 10:07 PM   #2
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Welcome to the forum, Dan.

Sounds like you had the beginnings of a good plan until others got involved.

Go ahead and post some pictures of what you have and we'll go from there. I can tell you that with a surface applied membrane, you have the wrong drain. But there are ways to get past that.

Not much sense in giving specific advice until we see what you have to work with, though.
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Old 03-26-2018, 09:08 AM   #3
milnerpt
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pictures attached:

not in any particular order, showing:

the sloped pan with drain

close up of drain

the shower wall with mixing valve (they seemed to run a few inches short of board and have a thin horizontal strip running, but they are butted closely)

the gap under one of the boards (I think this is the left wall)

the gap under another wall, where it is flush

I trust your direction as far as membranes, drains, and swapping things out.

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edit: i guess my next upload I can reorient things so you arent turning yourself upside down.... now that I figured out how to attach and upload the pictures.
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Old 03-26-2018, 11:33 AM   #4
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1. Drain won't work..now you can use an adapter kit that schluter makes to go from clamping drain to a bonding flange type. To do that you'll need to add to the pan. Doing so would also eliminate the gap under the backer. The drain may also be salvageable by doing the divot method, but from the looks you'll still need to add drypack and use proper fabric to tie a liquid membrane into the drain body.

2. I've never used that backer but those that I know who use it cover it with a liquid like ardex 8+9.
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Old 03-26-2018, 12:00 PM   #5
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Unfortunately Dan this "shower" was built completely wrong for what you were trying to do. It looks like you were going for a curbless shower? Unfortunately at this point there is no way to still make this a curbless shower with the drain setup you have there. Not sure what the plumber was thinking there.

IF you want to save what you were doing there I would get the Kerdi Drain with the clamp drain adapter. You'll have to build a curb and then do a proper mud bed sloping to the Kerdi drain. This will also embed your wall board into the mud bed eliminating the gap problem at the bottom.

The question then is do you Kerdi the entire shower or only up to a certain point above the curb? If it were me I would Kerdi the entire shower. Now I'm not 100% sure about the compatibility of that wall board with Kerdi (you could call them). For sure you will need completely unmodified thinset because you will be sandwiching the thinset between two moisture barriers.

If you still want a curbless shower you will have to bust up that concrete and set your Kerdi drain and pour a new slope.
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Old 03-26-2018, 02:45 PM   #6
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To clarify the two different aspects and addressing them separately:


1) The drain. Is this considered a 'traditional clamping' model? If I understand correctly, the reason it would not work is that it would allow for drain water to basically wet the concrete 'pan', which has no rubber liner underneath. I understand then this would not be a waterproof system, however is webt concrete really a big issue if there is nothing beneath the system that minds being wet?

Ive seen the one post about the 'divot' method - versus using the conversion kit, but both would involve basically raising the level of the 'pan' to allow for reslope. How much does the conversion kit raise the level of the drain? I may be more inclined to do that, if I am looking to re-slope it either way.

As for re-sloping with drypack, I may still be able to re-slope and keep a very minimal curb (I think ive seen posts regarding creating this with bricks and then thinset?)


2) the board - I plan on covering this with some sort of additional protection. I havent heard of the Ardex 8+9, although it looks more like a slurry you paint on (similar to kryton products I used to waterseal concrete walls) as opposed to liquid redguard/aquadefense/laticrete etc.

Kerdi requires unmodified thinset, although this board recommends modified thinset on it and covering seams. Additionally Im thinking Im more comfortable with a slurry/liquid to apply, unless the drain does not allow for a slurry/liquid method.

Obviously the board seams and penetrations need addressed (fibermesh tape then liquid, if I use that product), but how to address the gap if I do not raise the level of the pan? Is there some sort of back-filler (polyurethane caulk, strips of cementboard) that can be used then covered with the topical waterproofer as well?


Curbless would be nice, but Im not against a small curb. In what I actually do for a living, a small curb is not a barrier to accessing a shower for anyone. You just need proper door width. And a built in bench is silly and obstructive. A small curb would also do a little better at water control (obviously). Rather than a random search of shower curbs which would lead to an hour of random thread-reading, does anyone have a more succinct and forthright thread on a small curb?
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Old 03-26-2018, 02:53 PM   #7
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1. Yes. You'll end up with mold and mildew along with a pretty nasty smell. Yes you will end up with additional height. Can't remember exactly but I think about 1"-1.5" at the drain.


I think at this point I would just bust out the concrete and start from scratch with the pan. Then come up with a sound plan rather than having so many "what if I go with this and that".
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Old 03-26-2018, 06:03 PM   #8
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There are two general classes of cement board: fiber-cement, and 'real' cement boards. YOu need to find out which type you have unless you are going to cover the entire shower with Kerdi (or a similar sheet membrane). You cannot embed a fiber-cement board in your pan and use a conventional liner. You should not use a waterproofing sheet part way up the wall as moisture can get into the board, and then the only way it can get out is back into the structure...the membrane will stop it evaporating into the shower. You're required to install a sheet membrane up to at least the height of the showerhead.

The problem with just letting moisture go into the ground under your shower is many facetted, moisture draws roots, carpenter ants, and termites (see any of those in FL?!). ANd, depending on how wet it got, wick up and rot out the wooden plate and maybe the lower section of the studs. Most places in FL are wet enough...you don't want to add more into your structure.

A full covering of the shower with a sheet membrane means that there is very little to get wet during a shower, it will dry out significantly faster than a more conventional build, which means it will minimize the likelihood of mold and mildew forming (see that in FL?!). You still need to keep the shower clean of soap scum, body oils, etc., as that's the food that the mold grows on, but if you minimize the moisture available, you limit it considerably.

While it may be possible to mix shower system components, it's a bit risky unless you have a lot of experience. The bits are engineered to work together.

If you insist on a modified with Kerdi, Schluter DOES sell one. There are others, but without understanding the specific characteristics of the modifier chosen, it may or may not work under or over Kerdi.

When tiling ANY cbu, you should wipe it down well with a wet sponge prior to spreading the thinset. Many of them literally suck way too much moisture out of the thinset, making it dry where it needs to stay wet to flow and embed the membrane (or the tile, for that matter). One benefit of a modified is that it tends to hold moisture longer, but with a membrane, that is not always a good thing. You'll see a huge difference if you do wet the surface down first.
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Old 03-26-2018, 07:54 PM   #9
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Busting up the whole pan is about the last thing I want to do. If Im busting up concrete, Id rather just get at the drain area with a concrete saw and replace it with a standard schluter drain.

Im willing to forgo the curbless, can set the kerdi conversion drain, and would bury the bottom edge of the diamondback board.

Is a kerdi conversion drain compatible with a liquid membrane? I think I saw a post of how this was achieved in some thread deep in my memory. Id really prefer a liquid membrane over kerdi - given that the diamondback board wants modified thinset applied to it (which kerdi wants unmodified).

Is there a minimum recommended depth of a dry pack bed ( ie no less than 4" of drypack?) Can I keep it to the 1-2" that the kerdi adapter drain will require?
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Old 03-26-2018, 08:06 PM   #10
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With a bonded mud bed you can go to almost nothing. You'll have the 1" or so at the drain, then add in the necessary 1/4" per foot pitch.

I've never done a kerdi drain with liquid, nor is it designed to be used that way. But...that's not to say it won't work. There's just no testing to say so. If you arent doing a full schluter shower then there is no need to worry about what type of thinset schluter wants you to use. I haven't used an unmodified thinset in probably 4 years in conjunction with schluter materials.
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Old 03-26-2018, 08:30 PM   #11
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https://www.schluter.com/schluter-us.../p/SET_ALL-SET

As I said, if you really want to use a modified thinset, and want to keep it all Schluter, that one listed DOES work. There are others that will as well. WHat you do NOT want is one that uses latex as the modifier...there is an assortment of things that can be used to modify thinset...latex needs to dry, and that doesn't happen between a waterproof membrane and something like a dense porcelain tile. Other modifiers will become stable, the cement will always cure.
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Old 03-27-2018, 08:44 AM   #12
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Thanks for the continued direction.


1) As the schluter adapter drain may only be compatible with schluter membrane, do any of the liquid membranes make an 'adapter' drain?

Looking at the laticrete site it looks like they just have their drain, but no 'conversion' style.

2) if there is not a liquid membrane adapter available, it seems as if Im going to need to use a membrane on the floor. Ive seen other threads on using membranes on floor and liquids on the walls. In theory (voiding warranty aside), this should still be watertight. Im sure many will remark 'stick to one system', however i may have more faith in doing something that should work well in theory. Given the modified vs unmodified, getting kerdi to stick to the walls - as jadnashua remarks - getting that kerdi to stick may be problematic on this diamondback material. that would be sandwiching thinset between two water-impervious layers and would lead to ???

Otherwise I am looking at ripping out and replacing diamondback with cement backer.

3) Im not planning on ripping up the whole pan (its not dry pack, its poured concrete), however how feasable is it to cut out a 6"x6" (or whatever size) to replace the drain with a different one? Im assuming this would be terribly precarious, but maybe isnt as challenging as the pipe is buried in concrete and protected.
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Old 03-27-2018, 01:33 PM   #13
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Dan you can use a Schluter drain with a liquid membrane (I would use Hydroban if using a liquid for your pan with fabric in the corners and changes of plane and also at the perimeter of the drain). People did that for years on this forum before Laticrete came up wit their own bonding drain style. Is there a reason though why you want to use a liquid membrane for a shower pan liner vs Kerdi? Of course there is no warranty however with a mix match setup like that...
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Old 03-27-2018, 08:23 PM   #14
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Thanks ZZZK for the instruction.

Im thinking you just use the laticrete membrane fabric rolls for the corners and changes of plane? If you are talking about using schluter, do you embed the strips in thinset, or in a layer of the liquid membrane?

as far as avoiding fabric in the pan, Im really not against that. Im against fabric on the walls (lest i tear out all the diamondback). And I figure if I am putting liquid on the walls, may as well go with the floor as well.

No matter which way I run it, Im not worried about the warranty. 10 years from now, if something happens, as a homeowner am I really going to go through the legwork to file something like that? Are they going to look down on the homeowner, not the contractor, even if I follow their letters to a T? If the products are so great, why even worry about needing a warranty?


I figure my two realistic options at this point are
1) kerdi adapter, new slope of drypack, a curb, and hydroban

2) cutting concrete out around the drain, chiseling out a hole to reset the drain with a proper flange drain, covering the gap at the base of the boards, and installing product - now that I think of this, I could use laticrete flange drain, hydroban, follow the steps, and likely come out with a warranty?

hmm. I do have my diamond angle grinder and concrete saw blade on a skilsaw. Maybe that wouldnt be as difficulty as first thought. How deep under the exposed part of the drain would I need to dig in order to re-set a proper drain flange? just an inch or two? I do have hydronic tubing running down there at 4" deep.
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Old 03-30-2018, 06:12 PM   #15
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Follow up after contemplation, measurement, and research

There is a 1 1/8" drip from floor level into the pan (seen in the first few photos) at entrance to the shower. The top of the drain to the pan is also 1 1/8" if the drain is fully lowered as far as it can go. and the pitch appears correct - seems to be 1/2" drop

Given this 1 1/8" depth, why wouldnt the 'divot' method be appropriate in this case, and use the same drain?

Im not sure how much depth should be allowed for the membrane, thinset and tile altogether, however 1 1/8" seems enough to slope a new layer of drypack mud, create a divot (although maybe shallower than those in other posts), and just follow that divot method to use a liquid membrane on the entire install?

Thinset would be placed first, mud would be sloped, use a coffee can for the divot, etc etc. Perhaps I am missing something, or perhaps the drop in height isnt apparent from pictures (I certainly didnt mention it initially)

Id call the plumber who did this to ask him why he did it all in this fashion, but then again, I dont really trust what he would answer anyhow
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