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Old 06-29-2005, 02:15 PM   #1
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waterproofing joint between concrete floor and walls

Hi. The master bathroom in my under-construction home has concrete finish floors and the shower area is continuous with the rest of the room (wet room style, with no pan, curb, etc.) The shower area is 9' x 3' and the floor within this area was sloped to the drains when it was poured (it's slab on grade with insulation, radiant heat PEX and vapor barrier in case that matters).

What is the best way to waterproof the framed walls of the shower? My primary concern is with the junction between the wall and the concrete floor, because I won't be putting any additional finish material on the floor. Should I do like a tub surround/tub junction and hold the backer board slightly off the floor and then just caulk the joint? I'm planning on either tile or a mortar/stucco finish for the walls (to look like concrete). Is it advisable to use the Kerdi membrane material even though I can't continue it onto the floor?

I also want to put a seat on either end of the 9' length, and I found the masonry shower seat/monument FAQ extremely helpful. I will either cast these from concrete or build them of block and mortar, but again, how to transition from this to the framed walls and floor and be waterproof? Also, would the cold joint between the face of the seat and the floor need to be addressed in any particular manner?

Thanks in advance for any suggestions. This forum is a great resource.
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Old 06-29-2005, 08:35 PM   #2
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Hi Splatgirl,

You are going to need a pan liner. That or a waterproofing membrane of some sort, such as Kerdi.

If you want concrete as the finished floor, you will have to put it on top of the waterproofing in addition to what is under it.
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Old 07-02-2005, 11:21 PM   #3
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Thanks for the reply
Can you tell me specifically why I must have a pan? Since the floor already exists, putting a pan under the concrete is absolutely not an option, I'd like to be sure I know what I'm trying to overcome before I start making compromises or thinking about a solution...
(The floor can't leak anywhere because it's sealed concrete slab on grade.)
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Old 07-03-2005, 12:06 AM   #4
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Leaking is Not the Issue

Your concrete will, at some point, absorb moisture. Combine moisture, organic compounds like soap, sweat, hair, etc. and you have a mold farm.

I have a hard time understanding how this shower passed Code anywhere in the USA.
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Old 07-03-2005, 03:57 PM   #5
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Hi Splatgirl, Welcome aboard. Please give us a first name.

I won't argue with you about the floor, except to say that concrete is not waterproof, not regular residential grade concrete, anyway.

On the bench, I suggest the Better Bench from my friends at Innovis. It is simple to install to the walls and doesn't touch the floor at all.

http://www.innoviscorp.com When you get there, say hi to Gina (who is a member of our forums).
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Old 07-03-2005, 10:28 PM   #6
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Thanks. It's Holly.
Point understood on the concrete not being waterproof and mold thing. Waterproofing the floor beyond any doubt I think I can
handle, (epoxy comes to mind) but is that the only issue with what I want to do?

Forgive me if this is preaching to the choir, but I'd like to make sure I've got my info straight before I call the the local inspector to double check this...
My state code says:

"Subp. 3. Shower floors or receptors. Floors or receptors
under shower compartments shall be laid on or be supported by a
smooth and structurally sound base. Floors under shower
compartments, other than those laid directly on the ground
or where prefabricated receptors have been provided,
shall be lined and made watertight by the provision of suitable
shower pans of durable material. Such pans shall turn up on all
sides at least two inches above the finished threshold level.
Pans shall be securely fastened to the waste outlet at the
seepage entrance making a watertight joint between the pan and
the outlet. Finished floor surfaces shall be constructed of
smooth, noncorrosive, nonabsorbent, and waterproofed materials."

Regarding the bold text, is it accurate to say that this situation falls under the "those laid directly on the ground" category?

And the terms "waterproofed materials" is rather non-specific. Is there an acceptable method/convention for establishing a surface as waterproof?

I don't mean to be difficult here, I just really, really want to figure out a way to get as close to my ideal as I can and I'm one of those people that likes to be as informed as possible.

John- Thanks for the Better Benches link. I actually like the idea of a monolithic bench better as it's more suited to the look of the room. Is there a reason I shouldn't go that route if I can waterproof it? (Tiling this would not be out of the question for that matter.)
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Old 07-04-2005, 12:12 PM   #7
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One of your biggest problems will be the wood stud walls. Water will get to the floor plate and probably up the wall some by wicking through the concrete. Even if you used pressure treated wood, I think you'd have a problem. If there was a monolithic curb all of the way around it might have worked, but it doesn't sound like your floor was poured that way. You mentioned putting down expoy (paint?), I'd rather have tile. If you want it to look industrial, you could go with a grey tile, with grey grout. Concrete once it gets a buildup of soap scum is a bear to clean, and can get quite slippery. If you did tile the walls, and you used Kerdi, you could bring the stuff down onto the floor, thinset it in place that 1/4" or so, and the tile would hide that junction. Might work...you might want to talk to Schluter. Normally, they want a 2" overlap to ensure a fully waterproof seam. You might be able to use one of their trim pieces - Dilex for example. I think you can get it in grey; that might provide the waterproof seal you want if you then tiled the walls. I think you will not like the concrete floor for a shower...my unprofessional opinion.
Jim DeBruycker
Not a pro, multiple Schluter Workshops (Schluterville and 2013 and 2014 at Schluter Headquarters), Mapei Training 2014, Laticrete Workshop 2014, Custom Building Products Workshop 2015, and Longtime Forum Participant.
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Old 07-04-2005, 04:52 PM   #8
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Wow, a text of bureaucratese.

To help confirm that you want to cover concrete somehow (like with a layer of epoxy-concrete), I'll add this: I went to a scientific seminar about five years ago and heard a professor Aitcin show what high-performance concrete can do. Tons of slides, pictures, diagrams, charts -- a real eye-opener.

I still remember one cute picture of month-old healthy looking piglets in a pig house made of high-performance concrete. What has this got to do with a shower floor? Aitcin's expensive high-performance concrete did not let air into it (no pores) and so did not give safe harbour to all those epidemic-causing diseases that used to kill off the piglets every few months. The diseases used to keep coming back no matter how much disinfectant was applied. Concrete is porous in its normal state, and 'stuff' can go deep enough into it that you can't kill it with bleach or disinfectant. A floor is certain to pick up organic matter (soap is good food), and give a warm humid home to micro-organisms.

I have bare concrete floors (and walls and ceilings) in my place. When I am finished remodeling, I will be sure to leave no bare concrete exposed. Don't want to give mold and worse stuff any place to burrow into. I will cover every surface, either tile it, or add a layer of plasticized modified special expensive concrete that is guaranteed to be airtight and watertight. I am still exploring that world. If you have info or resources to share, i'm all ears.

Epoxy may be watertight, waterproof, but it may still crack. Hope someone with more expertise can comment more.
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Old 07-04-2005, 05:17 PM   #9
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Being practical:
1.) Plastic liner under your epoxy. Plastic corners made and sealed with the official glue that comes with the plastic. That is a shower membrane. (How far up the wall, hmm... And whether to build the shower walls with concrete or with wood frame + plaster, hmm...).
2.) Clamping drain. Millions installed, millions satisfied. Plenty robust enough to use in a concrete structure where there is no wood underfoot to collect eventual moisture...
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