Scrape off any peeling paint and sweep down walls to remove dirt or debris. The wall surface must be clean and dry before beginning.
Patch any holes in the wall with expanding hydraulic cement. Allow cement to dry for 24 hours.
Paint the cinder block wall with a thick coat of masonry waterproofing paint, pushing paint into cracks and crevices of block. A paint roller or brush made specifically for masonry is best. Allow to dry overnight or for a minimum of 12 hours between coats.
Cover the wall with a second thick coat and, if needed, a third coat. For the wall to be waterproof, the paint needs to thoroughly cover the cinderblock with none of the block showing through.