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Sealing slab around added plumbing penetrations

DenmarkDave | Posted in General Questions on

hi GBA

I have a bath in my basement.  The bath was added after construction but the roughed in drains were part of the build.  When adding the bath, some of the slab was removed to fit the drain.  The slab has 4″ of foam and  a concrete vapor barrier taped to all penetrations. The foam and vapor barrier have been disturbed by widening  this hole (originally formed and covered by a 5 gallon bucket – see picture).  The problem is that some of the drain is now level or somewhat higher then the surface of the slab.  What is the best way to ‘seal’ this opening?  I am concerned about vapor and air infiltration from this opening.

thanks in advance for any ideas

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Dave.

    I've patched slabs before, always with hydraulic cement, but only on older homes that didn't have poly or insulation beneath the slab. I'm sure you'll get some better advice than this, but it seems like you could seal the area with a few pieces of rigid foam and/or canned spray foam and then cover it with concrete for a neat patch.

  2. tommay | | #2

    Looks like a tub and shower drain. If that is the case, it needs to be accessible for service and replacement. I would only pour cement below the trap, if dirt is exposed, and or up the sides to the level of the floor, basically making a cement box, which could have been done before the full install of the tub. You can add regular fiberglass insulation around the piping if you like.

  3. Expert Member
    BILL WICHERS | | #3

    If it’s a dirt bottom hole (hard to see for sure), I’d use concrete patch to make a little “floor” in there, but not cover any of the plumbing. I’d use canned foam to “seal” the penetration, trying to get the vapor barrier and foam all foamed together so stuff things are sealed to each other. I’d probably stop there, but maybe make a removeable cap for the hole out of some plywood with an smaller piece glued to the underside of the cap to make the cap stay set in the hole.

    If I was feeling OCD I might use some XPS to make an insulating liner for the hole, glued together with foam board glue.


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