My circa-1932 garage has old-timey poured concrete walls. They've held up remarkably well, and many years ago, I had the interior walls sealed and waterproofed, to the extent that was possible.

Over the years, much of the coating that was applied (dark grey, with a rough texture) has held up well, but in a few spots, it has flaked off, exposing a powdery concrete surface beneath.

(Kind of a pain in the butt, since any time I brush against the wall to plug in my car's charger, I get some of this white powdery dust on me.)

I'd appreciate any advice for technique(s) and product(s) I can use to clean and re-coat these exposed sections of the wall. Doesn't much matter to me if it matches the dark grey color of the current coating...I just want to seal the dusty parts.

Thanks!