I had a geothermal furnace put in recently, and with that, the old heat pump was removed. The electric from the heat pump was run through a hole through the foundation to the panel. The hole is about 3 inches in diameter. The foundation is cinder block, there is a gap between the exterior and interior portion of the block. How do I patch this hole?

If I use the hydraulic cement or spray foam, won't it just fall into the cinder block gap? Do I get some wire mesh and slather concrete over it?

I like to pretend to be a DIY person, but really I don't really know what I'm doing most of the time. So any resources/products/ideas would be greatly appreciated!

1 Answer 1


Option one - toss enough mortar or hydrualic cement in the hole to fill up the core. Tedious, and annoying, but it works.

However, option 2 also works and takes a lot less material. Cut 4 strips of wire mesh or stiff screen about as wide as the widest part of the hole but longer than the hole. Tie long wires to the middle of these in pairs, arranged so that when pulled tight each pair of strips is at angles to each other. i.e. they make an X

Slack off the wires so the strips can be stacked on top of each other and slid through the hole while holding the wires. Once the strips are all the way in, pull the wires tight and tie to something outside the wall. Pack in some hydraulic cement or mortar and wait. Once that has set, you can cut off the wires and finish patching the hole. Do this from both sides (which is why you made 4 strips in sets of 2 - one set for each side.)

  • Thank you! This make sense. I will pick up some materials, give it go.
    – Nick S
    Sep 8, 2020 at 10:30
  • Got around to doing...9 months later. Seems to have worked! Thanks
    – Nick S
    Jun 26, 2021 at 23:31

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