I have a gas pipe that comes through my poured concrete foundation about 12 inches off the ground:

It is not sealed around the pipe on the outside. The gap is definitely large enough for insects to get through, and maybe small mice so I want to seal it up.

Googling this, I see a lot of mixed info - some ppl are saying expanding foam or caulk are OK, others are saying you MUST have a special sleeve. However, the sleeve stuff seems to be specific to underground penetrations through the wall?

So, I'm wondering is it OK to put expanding foam or caulking around that? Should I do just one or the other? Or should I pump foam deeper into the hole as thermal/ air insulation, and then after that's hardened, caulk around the outside for water seal? Or should I use some other product entirely?

Note that this is already in place, so something like a sleeve that needs to be put in place at the time the line is run is not an option.


Update: Based on the comments and suggested duplicate, I'll clarify that this pipe goes through a concrete tunnel at least 10 inches long. The suggested duplicate may be a solution, but if it is I need some clarification on whether I should be trying to get duct seal to completely fill that tunnel around the pipe. Or do I just seal the outside with duct seal? If the latter, then that means the rest of that tunnel is just empty. Does that matter?

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  • 3
    Does this answer your question? What to use to Seal gap between Pipe and Exterior wall
    – isherwood
    Commented Aug 31, 2020 at 15:34
  • Not sure why there are close votes this is a good diy question. The gas pipe installed today requires a flanged penetration since you have an existing install any of the spray foam or sealing putty’s, silicone sealers will work to block insects.
    – Ed Beal
    Commented Sep 1, 2020 at 8:15
  • I've seen the recommendations for duct seal, but I this is a penetration through probably 10-12" of concrete, and I can't see how I'd get a product like duct seal more than an inch or two into the tunnel in the concrete. Is sealing the very outermost part all that matters? I thought the advantage to the foam would be to further reduce heat loss and act as a secondary barrier to insects/ rodents if they make it through whatever's on the outside, whether that's caulk or duct seal.
    – SSilk
    Commented Sep 1, 2020 at 19:54
  • 1
    You'd seal each end to a depth of an inch or so (or just the outside if access is prohibited). Optionally jam some fiberglass insulation or something in there, but it's probably not worth the hassle.
    – isherwood
    Commented Sep 2, 2020 at 19:40
  • 1
    @isherwood That was a water pipe this is a gas pipe there are different laws regarding the 2 different types.
    – Ed Beal
    Commented Sep 2, 2020 at 20:38

1 Answer 1


I would use "duct seal". It's a putty-like material that's a bit sticky. You'll find it in the electrical department. It's much more robust than foam.

Caulk would be difficult to work with on a gap that big and would be more difficult to remove if you had to do any modification later. You could probably get good results with silicone, though. I'd go with clear or light gray. Don't use latex as it shrinks badly.

  • 1
    If mice are a concern i would stuff coarse steel wool all around the pipe first, Stuff it far enough down to allow for the duct seal, or any other product you choose. The mice can chew through many things but the steel wool should thwart them. ( that's right, i said Thwart.)
    – Alaska Man
    Commented Sep 2, 2020 at 19:33

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