I have a CMU foundation block wall in my garage that leads to my basement (picture below). Half of the cores are empty and it is about 8-9ft deep. I regularly treat this area and the garage with bifenthrin insecticide, but the open cores are continuing to attract tons of camel crickets to use as a home. I'm currently renovating the garage so I want to either either fill, cap, or finish the top of this wall off so it looks more attractive and eliminates an area for insects to live. I'm looking for suggestions on the best way to do this.

This foundation wall is from 1956 and half the cores are already filled. If I end up needing to fill them, I can do this by hand with a wheelbarrow and 5gal bucket and I was looking at Sakrete Maximizer Concrete Mix since it seems to yield the most fill per 80lb bag. The fewer I have to mix, the better. I would eventually seal and paint these walls leading down the stairs. Thanks!


This went well. Looks more finished now and the camel cricket numbers are dwindling. I screwed some 2x4s to the wall to make a form and only ended up needing about two and a half 80lb bags of concrete mix after filling the blocks with broken up pieces of rigid foam.

CMU block wall filled with concrete

1 Answer 1


To insect proof the block, you only need to fill the last 4" of block. Stuff newspaper in the core down a ways to keep the concrete of masonry mix from dropping all the way down.

Filling the whole core is not needed and to attempt to fill it from the top, through those small holes will only be frustrating. It will not go all the way down anyway. It will stick to the sides and other cross webbing you do not see and start collecting in places before it gets to the bottom.

  • I agree with Jack, no need to completely fill them.+
    – JACK
    Apr 20, 2020 at 17:32
  • I wouldn't use newspaper or any pulp product though, it may attract termites and although they would not harm the CMU, they might then move on to nearby wood. I would use Styrofoam peanuts and/or chunks from packing material, with some wax paper or cellophane on top to keep the concrete from leaking down into the peanuts.
    – JRaef
    Apr 20, 2020 at 18:14
  • Thanks, I didn't realize I could just fill the top block. I may have some rigid foam I can use.
    – Vincent
    Apr 20, 2020 at 18:34
  • @JRaef ,The blochould be a sealed unit from top to bottom. Yes newspaper is not the best choice if the termites can get into the newspaper, back out and then into the wood somehow. Yes that is possible I guess. Since the core of the block in question will be filled, it will not be through the holes that will be filled. But it may be through another avenue that is accessible anyway, newspaper or not. Never the less, the OP will use foam, problem solved.
    – Jack
    Apr 20, 2020 at 18:47

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