I need to drill a 1 inch hole in a basement foundation block wall to pass a 1/2 emt conduit through. How do I seal the gap afterwards to pass inspection, prevent mice, insects, rain and drafts.

Keep in mind it's winter in Minnesota, so any compound needs to be able to be applied in cold conditions.

Do I simply use duct sealer or something more solid.

  • Do you have any water leakage issues?
    – Ed Beal
    Jan 10, 2019 at 20:29
  • No, but the hole will be on a vertical face of the north west wall so it will get full exposure to wind and driving rain
    – bfoddy
    Jan 10, 2019 at 20:49
  • The hole will be about 4 feet of the ground in the walkout portion of a walkout basement
    – bfoddy
    Jan 10, 2019 at 20:53
  • if you are worried about mice digging through the duct seal, then jam in some steel wool between the conduit and the concrete ..... mice do not like to chew steel wool
    – jsotola
    Jan 11, 2019 at 2:13

2 Answers 2


I'd use duct seal. I don't think mice like chewing it much, and at four feet up it's fairly safe anyway. Keep it in your pocket until you're ready to apply it.

You could also use pure silicone or urethane caulk if the masonry is dry. Both are solvent-based and should still work fine in the cold.

  • I just want to make sure duct seal stands up to all the weathering factors of sunlight, cold, rain, etc for the long term. A power line entrance right next to the hole seems to be sealed with something harder.
    – bfoddy
    Jan 10, 2019 at 21:36
  • That's what it's for. It does tend to harden over time.
    – isherwood
    Jan 10, 2019 at 21:38
  • Duct seal would work great since its on a daylight basement I wouldn't be two worried, if it leaks it would not be hard to arrange some drainage.
    – Ed Beal
    Jan 10, 2019 at 22:32
  • I'll try it this weekend
    – bfoddy
    Jan 11, 2019 at 22:00

Besides duct seal and caulk, you could use a two part epoxy putty that bonds to both metal and masonry.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.