Basement wall cinderblock gap fill

Question

Basement wall cinderblocks. Found mice and am cleaning up that mess, noticed gaps in the top of the cinderblock wall. One of them I can see daylight through so there is definitely a crack that needs to be addressed.

I was intending on packing these with steel wool or some copper mesh and was on the fence with gap filling them. Are they necessary to be open? Some of them are packed with dirt/construction materials from a remodel but most are open on the top. Was this just the style of block or intentionally left open?

If it matters we have a french drain. Radon levels are ~1.5 +/- .25

Answer 1

They're not intentionally left open. Masons apply mortar to the two faces of the block and typically there's a gap left in between. It would be difficult to get the joints completely full without massive waste in the form of squeeze-out.

You can fill them with about anything that meets your needs.