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Best way to fill holes in concrete block foundation?

Posted by arcas (My Page) on
Mon, Jul 19, 10 at 0:03

Hi. Here's my situation. I have a crawlspace with concrete block foundation. I'd like to patch a couple holes that could easily allow mice to get into the crawlspace. Problem is, since this is a concrete block wall, it's hollow and so each hole is actually two holes (one on the inside face and one on the outside). Simply patching the inside face won't work...a mouse could enter through the gap in the outside face and then navigate up through the hollow blocks and enter the crawlspace at the sill plate.

I know the best solution would be to dig down on the outside and patch each hole/gap on the outside. I'd prefer to avoid that since there are some large nearby trees near both holes so I'm sure the ground is one big root ball in those areas.

Another solution might be to A) patch the inner gaps with expanding hydraulic cement like normal and B) fill the concrete blocks near each hole by squirting a low-viscosity concrete mix from the sill plate down into the blocks. The idea being that if a rodent did enter through the outside face, it wouldn't be able to navigate up through the blocks because they'd essentially be solid. There's no room to insert a concrete vibrator down into the blocks so the concrete would have to be mixed pretty thin to make sure it flows all the way down...probably cake batter consistency or thinner.

Question: has anybody done something like this? Is there a better solution that doesn't involve digging down along the outside?

Follow-Up Postings:

RE: Best way to fill holes in concrete block foundation?

I believe block is set into a bed of concrete on the foundation, so there shouldn't be openings down at the bottom as you suspect. As for the holes that need patching, I think you can stuff the hole with something so the mortar doesn't fall all the way down, then patch them.

RE: Best way to fill holes in concrete block foundation?

About the sane as patching a wall, just different materials.

A small hole you may be able to fill in stages with polyurethane caulk.
It will stick very well if the edges are cleaned of dust.

Larger holes a small support across the hole to hold a section of cement board.
Some wire through small holes in the cement board and wrapped around the stick across the opening on the outside.

Fill the hole part way with mortar.
Let it harden and cut off the wire flush, then fill the rest of the hole to flush with the face of the block.

Repeat on the other side.

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