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Thread: Concrete around ptrap to complete tub install

  1. #1

    Default Concrete around ptrap to complete tub install

    I have dry-fitted connecting my new basement shower/tub 1.5 " PVC drain with a ptrap.
    I am not sure how to seal up the concrete hole. At the base, the horizontal drain sits 3" below the slab, then a riser picece, and then ptrap which is right in the middle of the slab. The verticle tub drain piece seats correctly into the compression fitting on top of the ptrap at a few inches below the top of the slab.

    Can I put concrete all around the ptrap fittings (careful to not move it)?
    If not, I don't see how I can get a good seal; there is no long verticle piece that is not on the same level as the ptrap.
    I thought I read that connections for PVC plumbing should not be concreted in and that only a through pipe should be.

    Any other techniques to seal the concrete hole?
    Thanks!

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    You don't want slip joints below ground sealed in concrete...many people just leave it open and maybe put some sand in there. 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

  3. #3

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    Thanks for the reply.
    They are not slip joints but I probably still should not concrete them. All would be glued except for the top of the ptrap to receive the final connection from the tub drain.

    Sand may be a good option. I was hoping to make it air tight to keep dangerous gases out like radon (even though concrete is not 100%).
    I hope some more options are posted.

  4. #4
    Computer Programmer Bill Arden's Avatar
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    I had a problem with critters so I used spray foam under the slab to make a box.

    The critter chewed threw, so I added wire mesh and more spray foam.
    Important note Ė I donít know man made laws, just laws of physics
    Disclaimer: I'm a big fan of Darwin awards.

  5. #5
    In the Trades Gary Swart's Avatar
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    Slip joints are those that slide together and are glued. This is the normal way to connect PVC pipes. Dry fitting is usually not satisfactory to obtain a good fit because the pipe and fitting do not slip all the way together dry. If you force the fit, you may not be able to get it apart to glue it. You do not need a thick concrete slab around the drain. There is a foam band that is sold to shield the pipe before filling in the hole around the pipe with concrete, but that is not really necessary. You could use a piece of cardboard then fill in most of the hole with sand. A thin layer of mortar on top of the sand would work just fine. The foam insulation might be a good alternative as well. I would suggest you measure the fittings and pipe lengths carefully and not rely heavily on the dry fit as you will very likely come up short when you glue (actually, it's solvent welding) the pipe and fittings together.

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