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Drain penetrations in a slab on grade

amo675 | Posted in General Questions on

Hi, we are pouring a 5″ floating slab on grade with several cast iron drains penetrating through the slab.

the drain lines run in the compacted fill below the 4-6″ compacted gravel, 6mil vapor barrier, 2″ tongue and groove xps and the 5″ 4000psi pour with 1/2 radiant pex throughout.

the assembly we are planning on was to cut a hole in the vapor barrier and attatch to the cast iron pipe with tape, then cut a hole in the insulation around the pipe and fill with spray foam and finally to wrap the segment of the pipe that would be in contact with the concrete with thin foam insulation..

does this sound appropriate?

thanks in advance

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  1. GBA Editor
    Martin Holladay | | #1

    Everything you describe sounds fine to me. Some builders use one of the high-quality European tapes instead of spray foam to seal the gap between pipes and rigid foam insulation, but spray foam will work.

    Once your concrete has cured, you'll probably want to rake away some of the "thin foam insulation" you used to wrap the pipe where it penetrates the concrete. Then you can caulk this joint.

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