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Thread: Shower stall on basement slab

  1. #1

    Default Shower stall on basement slab

    I would like to add a shower stall where the rough in had been completed for a tub in my basement. I've included a picture that shows what I'm working with. I've done a kerdi shower once before with a mud base so I'm not opposed to going that route again or even using a kerdi tub-replacement pan. The kedri pan comes with a 10" offset to fit where the drain would go on a standard tub install.

    There is a trap in the cast iron line that lies beneath the concrete so my question is what is the best way to proceede with adding a shower stall? Can I connect a Kerdi drain to this tub line? Would I need to remove the over flow and cap it off right above the shoe?

    I was told that I need a trap under the shower pan. Do I really need to add another trap under the shower pan if there is one under the concrete?

    I guess I'm wondering why this setup would be okay for a tub but not a shower stall?

    I'm trying not to break up the cement at all costs.

    Thanks in advance!!
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  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    THe Kerdi drain is designed for a 2" drain line to meet US codes...what is the diameter of the tub drain?

    My guess is that if you want to get this inspected, you'll need to break some concrete. Now, it may be that the only part that is 1.5" is the trap (somewhere I think I heard a 2" line was required under a concrete floor?).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3


    The pipe under the cement 2" cast iron which ties into a 4" cast iron line. The pvc pipe you see in the picture is 1 1/2".

    I had posted the same issue in the John Bridge forum at the same time and the responses I'm getting are the same....break the cement

  4. #4
    Plumber Cass's Avatar
    Join Date
    Nov 2005


    Yup, thats what you need to do.

  5. #5
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Yakima WA


    Breaking concrete isn't as bad as you might think. A rotary hammer will work without killing you off like a construction grade jack hammer. It will get dusty. An option would be to hire a company that cuts concrete. Would cost you, but it would save you the work and it's clean.

    You've got a couple of problem that I can see. The first is you have broken a rule of drain installation when you went from 2" to 1-1/2". You never reduce the size of a drain as it heads to the sewer. It also appears that the drain will be too high for the stall to rest on the floor. Break the concrete and install the drain and trap properly.

    Last edited by Terry; 12-15-2009 at 04:16 PM.

  6. #6


    Thanks for the feedback guys. I'll be breaking up the concrete next week.


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