Question about filling around the vertical pipe for a shower drain in a concrete pad.

Discussion in 'Shower & Bathtub Forum & Blog' started by Mark In Florida, May 19, 2020.

  1. Mark In Florida

    Mark In Florida New Member

    May 18, 2020
    I moved the vertical drain for my shower about 5 inches, and I've seen two ways to fill in the hole. In one method, a 4 or 5 inch pipe is fitted around the vertical pipe, and cement is poured around that pipe, leaving the 2 inch pipe not covered in concrete. The other method is to just cover everything with concrete, including the outside of the 2 inch vertical pipe. I've watched a bunch of videos on concrete drains, and people do it both ways, but never once has anyone explained why they do it the way they do. I had planned on filling the bottom most part of the hole with gravel, and filling it the rest of the way with quickcrete. I'm in Florida, by the way, where the ground never thaws, if that makes any difference. Thanks for any advice!!
    Last edited by a moderator: Jun 4, 2021
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Well, I think you meant the ground never freezes! But anyway, you likely will need some space around the pipe to enable the drain to be attached, as it slides over the pipe. You normally wouldn't want your preslope to be so thick, that the entire drain hub could fit while having the slab filled in tight to the pipe. It's probably a good idea to sleeve the pipe that might be otherwise in contact with the slab with some foam so there's a little room for motion as things expand and contract with temperatures.

    It somewhat depends on the construction method you choose for your shower. A conventional shower with a liner needs the drain fully supported right up to the pipe eventually. Using something like a bonded, sheet membrane to build your shower, the drain flange is huge (in the order of 12" across), and those can support up to about a 5" diameter circle to allow the bell and socket of the drain to be low enough (the larger outer flange supports the drain in that case, which must be on solid 'ground').
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