From what you're describing, it sounds like you want to do the shower pan when they pour the concrete, and then just thinset everything?

Thanks for the quick response. - " it sounds like you want to do the shower pan when they pour the concrete, and then just thinset everything?" - Yes, I want them to cast the shower pan into the slab.

Sorry to be so dense, but I'm not sure I understand want needs to be to done to accomplish that. One installer I talked to said I just need to have him put thinset directly on the slab. However, I thought I read here that that was a bad idea and I should request a Kerdi membrane between the slab and the tile? From reading the Schluter site it seems that I need to use a Kerdi drain that is set flush with the surface under the membrane. I am confused about how to do that with slab construction.

I'll fire off a couple of quick details here.

The top of the curb needs to be a code minimum of 2" above the top of the drain. Floor pitch is 1/4" minimum to 1/2" maximum, so with your curbless installation the sloped part of your floor (ie, the beginning of your sloped "pan") needs to begin 4' to 8' from the drain. Or that distance could change with a graduated slope. That's how it's interpreted and enforced in my locale at least.

By casting the pan at the time the slab is poured, you'll be depending on the flatwork crew to shape your pan. That can be risky.

My first choice would be for them to form out the sloped pan area at an approximate 3" lower elevation, essentially stepping the floor down in the pan area. That way you get a complete integral pour with your tubing covered. Box out a small area, 12" square or so, for the shower drain, with the drain stub sticking out vertically. After the flatwork guys are done, the tile guy can add the slope inside the stepped down area while installing the Kerdi drain.

An alternative would be to form out the area of the pan with lumber, and not fill that area with concrete at this time. Have the pan poured and the drain installed at a later time.

You have radiant tubing in this area? If pouring part now and part later, the tubing can be run and the formwork can be notched to accomodate the tubing. I've done that a few times when doing partial pours.

There's also the detailing that needs to be done to the underside of the slab that makes up the sloped pan, since the pan will be in direct contact with earth. Again, based upon the experience of the crews that I deal with I'd rather have a tile guy take care of that instead of a concrete flatwork crew.

If you have it all done now and the poured slab is properly detailed, then yes, Kerdi and/or Ditra can be thinsetted directly to the slab.

Mongo

Mongo - Thank you very much. Your first choice makes sense. I was very nervous about asking the concrete guys to do something that is not standard operating procedure for them.

You said - There's also the detailing that needs to be done to the underside of the slab that makes up the sloped pan" Â does this apply to doing the continuous pour with the 3" lower elevation. I was planning to have the radiant tubing run in the shower area (it seemed like warming that area would be a good thing). How do I have the tile guy do it if I go with the your first choice?

Thanks again.

--markM

Floor pitch is 1/4" minimum to 1/2" maximum,

Per running foot to the furthest wall. :-)