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Thread: New Shower Drain in Concrete Slab

  1. #1
    DIY Junior Member
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    Default New Shower Drain in Concrete Slab

    Hello! I'm new here!

    I am adding a new tile shower to an existing half bath in my home in order to make it a full guest bath. I need to find detailed instructions (ie: step by step) for the process of adding a new drain in a concrete slab. I understand the process of cutting into the concrete and laying a new drain line, with space for a trap, and tying into the main line/vent. I am just looking for details that will help me complete the project such as:

    The easiest/best way to cut the concrete without damaging the slab/pipes.
    The best path for running the drain, with proper widths/depths.
    The correct fitting for connecting to the main drain and how to install it.
    How much of a stub up on the shower pan side.
    How to secure the PVC drain when I backfill with concrete.

    Just to give some background, my shower will be 40" x 40". It is roughly 3-4' from the main vent/drain that is also shared by a washing machine drain and bathroom sink drain on an adjacent wall.

    Thanks for your help. I have had trouble finding "how to" help on this topic.










    How big the trench in the concrete needs to be.
    How to cut the cast iron pipe and add an elbow for the new drain.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    Check out www.johnbridge.com.

    Some of what you need won't be known until you find out what is already there under the floor. You'll need to run a new vent for the shower, but it can join with that from the toilet and sink at a minimum of 42" above the floor. The drain for the shower needs to be 2", and depending on where you live may dictate the size of the remaining drain pipe (i.e., you may have to convert to 3" or even 4" to meet local codes for pipes underneath a slab).

    Unless the slab is a post-tensioned one (embedded cables that are under tension), there aren't that many rules on the best way to tear it apart. Scoring the slab and then cracking it up works. A deeper cut with a concrete saw is cleaner. You need to ensure the concrete you replace bonds with the existing slab, so you probably want to drill some holes for rebar dowel pins, and you can paint the edges with a slurry of concrete or mortar to help adhesion when pouring new concrete back in the hole.

    The height of the drain depends on the type of drain used. You may want to look into Kerdi from www.schluter.com. A neat way to build a shower.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Junior Member
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    Thanks for your reply. I don't know if it changes your advice any, but the pipe that I plan on tying into is the main vent- a 6" cast iron pipe that the washer and sink are also tied into. Those two are tied in above the slab- 6" up for the washer and about 15" for the sink. I plan on tying in below the slab, but above where the vent joins the main sewer line running out of my house. Would I still need a separate vent for the new drain?

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    Many places don't like wet vents...if that line is a drain for things above, by definition, it is no longer a vent, so yes. I'd be surprised if it is 6", drain pipe is measured by ID...cast iron might be close to 5" OD if it was a more normal 4" drain line. Wet vents tend to work better if the drain is oversized, so maybe...see what the pros have to say.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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