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Unread 10-21-2019, 10:25 AM   #1
april lau
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Help! New curbless linear drain shower

Hi guys! New to the forum. I've been reading the posts and found lots of useful suggestions. (Should have come earlier before we made the mistake)
We are currently working on our house project. First time builder and owner .Our plan is to have a curbless shower with linear drain in our open concept master bedroom. And we'll tile the whole floor of the house (as shown in the photo).
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Not knowing that we need to drop the subfloor to create a curbless shower, we built it at the same level with the rest of the house, only pre sloped it by 3/4in through the 4ft shower area. Now that we have floor heating and drainage pipes running under the subfloor, sinking it won't be an option. And we still want that curbless transition to the rest of the house, which will be tile on Ditra on 3/4in Plywood.

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We came up with 2 plans: First, use Redgard on plywood and reinforce it with fiberglass mesh tape for waterproofing. Then Ditra on top for crack prevention.
Question about this method is that Redgard didn't mention about it being used as waterproofing directly over plywood, only as crack prevention. So we are wondering if we can reinforce it with fiberglass.
Second plan is to put 1/4 Durock on plywood, then use Redgard as waterproofing and crack prevention. We don't know if Redgard is good enough crack prevention for large format porcelain tiles.

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Any suggestions?
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Unread 10-21-2019, 10:43 AM   #2
april lau
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We also did a little experiment with Redgard and Ditra. We tried to glue Ditra to a piece of cardboard with Redgard, instead of thinset. They seem to bond pretty well. When we try to pull them apart, the fleece on the underside of Ditra delaminated from Ditra instead of Redgard. And the combination is pretty flexible too, we can bend and roll the cardboard without breaking it. It seems easy to apply too, we struggled a lot trying to press down Ditra to make it bond well with thinset. We are wondering why nobody use this method. Is there any potential problem?Name:  IMG_7976.jpg
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Unread 10-21-2019, 12:57 PM   #3
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Welcome, April.

Not sure why you indicate that your shower floor area cannot be lowered for proper slope. While it's sometimes inconvenient, there is always a way to do that. As it stands now you have inadequate slope to create a shower receptor. The code requirement is a minimum of 1/4" per horizontal foot of slope to drain.

You cannot use RedGard as a waterproofing layer over plywood for your receptor. You can use it over properly installed CBU in that application if you apply the RedGard per the manufacturer's instructions and are willing to disregard the ANSI Standard that says you can't use CBU as a shower floor. That may be why Custom doesn't indicate their product in that particular application. I would not personally use that or any other liquid applied membrane for a shower receptor, but it's done alla time and that's entirely up to you.

As to the reason most folks don't use RedGard to bond Ditra to a subfloor might be the manufacturer's statement under Limitations in their TDS where it says "Do not use as an adhesive." I wouldn't recommend you do that, but if you elect to do it I would certainly recommend you create a test area where you can complete the tile installation and subject it to some foot traffic for a while. "A while" in that context might be as long as you want the installation to last in real life. It might work. It might not. Neither product manufacturer will be your friend if it doesn't.

My opinion; worth price charged.
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Unread 10-21-2019, 03:20 PM   #4
april lau
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CX, Thank you! Maybe I wasn't clear, we do have a proper 1/4in per foot slope on our subfloor. We dropped the 2x12 floor joists to create the slope when we did the framing. We just don't have enough depth for a mud bed. And we can't use shower pans either, because they are all pre sloped. I don't know if there's other waterproofing product that we can use directly on plywood. It has to be either thin enough so we can put Ditra on top, or similar thickness to Ditra so it can replace Ditra and also act as crack prevention material.

Any thoughts?
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Unread 10-21-2019, 03:27 PM   #5
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Quote:
Originally Posted by April
...only pre sloped it by 3/4in through the 4ft shower area
I was going by your initial post, April, and that's not sufficient slope.

1. What is supporting these 2x12 joists and what is below this floor?

2. Have you evaluated the overall joist structure and subflooring to determine the suitability for a ceramic tile installation at all?

I know of no manufacturer of direct bonded waterproofing membranes that is going to recommend his product over a wood substrate for a shower floor application. Might be one out there, but I've not run into such.

My opinion; worth price charged.
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Unread 10-21-2019, 04:36 PM   #6
RichVT
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In my experience, water will splash a lot more than 4 feet out even with a rain head showerhead that has a gentle stream pointing straight down. 6 feet would be more realistic.
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Unread 10-21-2019, 04:39 PM   #7
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A fiberglass cloth and resin over plywood pan could be built in place, but the warranty would be all on whoever installed it as it's "site engineered".

I've read where it's done on exterior decks that slope to drains, (usually scuppers) and within the last year or so a poster here showed pics of a shower pan done that way. I've no firsthand experience with shower pans, but have some with firberglass layup in general.

It would seem viable to me, but it would be hard to recommend to a client with my limited experience. Some years ago I knew of it being done on a commercial project (prison), but know zilch beyond that.
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Unread 10-21-2019, 04:55 PM   #8
april lau
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CX
Sorry it should be 1in over 4ft. The 2x12 floor joists are sitting on 5ply 2x12 beams. They are spanning 14ft at 12in oc under shower area, and at 16in oc under toilet and vanity area. I used the calculator, the deflection is L/822 for shower area and L/617 for toilet area. The rest of the house floor is built with 2x12 at 16in oc, spanning between 9 to 14ft, so L/617 is the minimum. Maximum about L/1626. And we used 3/4 T&G exterior plywood for the whole subfloor. The plan was to tile over Ditra over plywood.
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Unread 10-21-2019, 05:15 PM   #9
april lau
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Thanks Rich,

I agree. How about if we waterproof the whole 9.5ft floor? I hope it can survive some splash without the slope...
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Unread 10-21-2019, 06:34 PM   #10
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Quote:
Originally Posted by April
Sorry it should be 1in over 4ft.
Yes, Ma'am, it should be at least that, which was my point.

Again, what is below this floor?

Your structure, as described, is certainly more than sufficient to the application and might well lend itself to ripping down the tops of the joists. That's not usually a recommended procedure, but there are times it could be prudently done.
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Unread 10-21-2019, 06:47 PM   #11
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What thinset did you use that failed to stick the Ditra to the plywood?
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Unread 10-21-2019, 09:32 PM   #12
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We used this on top of durock, then Ditra. When we started tiling the next day, we lift up one tile to check the thin set coverage, and a small area of Ditra got detached from the cement board. Also it doesn’t seem to bond well with Kerdi band either, which we used over Durock around wall corners, some part came loose the second day.
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Unread 10-22-2019, 10:18 AM   #13
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Having just completed my own 42" ish wide by 84" ish long curbless shower, April, with the fixed shower head at one end, Rich is correct - water will travel farther than 4', with quite a lot of splash, really.

While you could water proof the whole floor the significant amount of water that splashes beyond the 4X4 area of the sloped floor will have no way to reach the sloped floor. Once again, I can assure you water accumulation on the flat floor will be significant.
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Unread 10-22-2019, 03:59 PM   #14
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Your shower head is facing which way?
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Unread 10-22-2019, 06:16 PM   #15
april lau
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The shower head is facing toilet
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