Kerdi shower pan and drain over dirt?

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Scouper

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I'm putting a small 30x30"shower in the basement. Id like it to be curbless so I'm cutting 30x30 into the slab (drain trenches over to sump and ejector pump). Can i use kerdi drain with a trimmed kerdi pan...and avoid having to pack the mud slope? The dirt under the slab is firm dry clay. Could i put down crushed rock or sand over dirt to make a base for the kerdi pan? Or pack mud flat over dirt? Maybe premade pan not recommended here? Thanks for any guidance.
 

Jadnashua

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While a recess would be necessary to do a curbless shower without raising everything outside of the shower, as said, it does need a structural slab underneath it. FWIW, clay is a lousy base for anything structural...it tends to expand and contract somewhat radically from moisture changes...that could easily be ground moisture, since a properly done shower pan should not be adding moisture there.
 

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Ok. So dig out additional depth, then repour concrete to the appropriate level to make a recessed pad to support the kerdi shower tray and drain assembly.
 

Scouper

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Ok follow up. How about a dry packed mortar shower pan over the dirt.? Trying to avoid digging out deeper and repouring.

20171115_123533.jpg
 

rufunky

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Ok follow up. How about a dry packed mortar shower pan over the dirt.? Trying to avoid digging out deeper and repouring.View attachment 43038
Just wondering how you made out! I am doing the exact same thing and there is next to no information on the web about this.

I am at the exact same stage as that last picture you posted except I have installed my plumbing, bonded drain flange and gone ahead and put a 1.5" top layer of gravel down.

The next step in my plan was to fill in the area with a 1/4 per foot sloped mud bed consisting of a 5:1 ratio as was recommended by Roger AKA "the floor elf".
 
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Jadnashua

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Having the shower essentially an independent structure verses the rest of the slab just risks potential movement problems. Plus, deck mud is quite porous, so, while the membrane is waterproof, it is not designed for water pressure from below, and that could allow moisture to wick up into the structure behind it. Deckmud is reasonably strong in compression, but any movement, and it could crack. It really wants a solid base. If your soil is really stable, it might work. Personally, I'd want a recessed slab there, that was mechanically attached to the rest of the slab via rebar. I'd also try to get a moisture barrier beneath it, but that may be tougher.
 
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