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As part of a conversion/remodel of a crawlspace into a basement on a 1997-vintage home, I need to fill-in 3 foundation vents that were installed when the foundation was poured.

Ideally, from the outside of the house, I’d like to fill the vents with concrete but I’m trying to do this right the first time.

I can attach a piece of plywood with a small hole and “spoon feed” the concrete into the vent cavity to fill it.

I wonder if i can use some type of “concrete patch” and fill these vents like a drywall installer would fill a hole in drywall.

The vents are approx 12″ x 6″ x 5″ deep
and are plastic. Any ideas would be appreciated.