Crack-Pac Flex-H20 is a single-component hydrophobic polyurethane that's ideal for sealing both leaking and non-leaking cracks in concrete and solid masonry. It is packaged in a single tube cartridge that is dispensed from a caulking tool. When the resin encounters water as it is injected into the crack, it becomes an expanding foam that provides a flexible seal. Simpson Strong-Tie Anchor Systems, 800-999-5099, .