How to Patch Hole in Concrete Wall

[sinTAKS]

I'm currently remodeling my basement and am at the demolition stage. The previous owner had chiseled holes into the concrete block to house the electrical boxes. Unbelievable, I know. Well, upon removing the boxes, I've found that these holes are deeper than expected. He chiseled through the block into the cavity, which in turn connects to every cavity of every block above and below it. (I'm getting angrier as I type this.) So, you see my dilemna. I've patched concrete before, but not like this. Can't just patch over it...there's nothing to hold the concrete. If this were drywall, I could put a board in there to hold the compound. Is there a similar fix for my situation, but using concrete? Do I have to pour enough concrete in there to fill all the cavities of the blocks below it until I reach the height of the hole in question? Should I fill the cavity with sand? If anyone has any information it would be most appreciated. Thanks in advance!!

[HayZee518]

It IS normal to chisel into concrete blocks to install electrical boxes. The boxes used are called concrete boxes and are made for the purpose. They are interconnected using emt conduit.
Anyway you want to fix the block. Regular mortar repair will just fall out. Hydraulic cement expands when it sets up - usually in about 20 minutes. Ever see one of those silly putty eggs? That's the consistency you want to make up with the hydraulic cement. Put it in there little at a time and build up from the bottom.

[sinTAKS]

Seems strange to tear into the foundation for the purpose of housing an electrical box. Couldn't that cause moisture issues? Seems like it has in my case. At any rate, thanks for your help. Someone else advised a similar solution, but said to fill the cavity with sand and then use the hydraulic cement. Sound right?

[HayZee518]

you can fill the cavity with sand or vermiculite. vermiculite might be better as a sort of insulation. Sand will retain moisture. an opening of 2 inches by 4 inches doesn't appreciably reduce the strength of the block

[mrcaptainbob]

Would that spray foam in a can be a good filler? Wad some newspaper in the bottom of the holes and then fill most of the cavity with the foam and then slather the cement over that.