In an attempt to run Cat6 Ethernet cables to my living room, I cut a handy box sized hole in the the block, but was unable to run the cable down from the attic at the top of the wall (it was obstructed about 3 feet up or mid way on the wall). In the end we put the connections in the ceiling. Now there is a 1.5x2.5 hole in the interior side of one concrete block.

  • My thought was to fill it using expanding foam and drywall mud.
    • What is the best way to fill it properly?

1 Answer 1


There are as many ways as opinions.

My suggestion would be to use mortar mix. Several layers, letting it cure between them. One to rough it in, and at least one more to assure coverage and finish.

I would not use foam and drywall compound. They are different from the material in the wall. Also drywall compound may not be ideal in places like a basement, which might be more moist than the rest of the building.

  • Thanks Mongo. for mortar mix, ill need to build up around the hole to hold the mix in place; but it should be stronger and a more similar material to the original block. And unfortunately its in the middle of a living room on the main floor.
    – mark f
    Dec 7, 2020 at 16:20
  • I would do the mortar mix in layers. If it helps you could put a lathe of pressure treated lumbar behind things with construction adhesive, to support the backside while you butter layers on.
    – mongo
    Dec 7, 2020 at 16:27
  • Creative troweling could make things look similar to the block, especially if it is painted.
    – mongo
    Dec 7, 2020 at 16:28

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