Crack-pac Flex-H20 is a hydrophobic polyurethane injection resin designed to seal leaking cracks, voids or fractures in concrete or solid masonry. The polyurethane is packaged in the cartridge and an accelerator is packaged in the nozzle. When the two are combined in the cartridge and mixed, the result is a low viscosity, water activated polyurethane. When the resin encounters water as it is injected into the crack, it becomes an expanding foam that provides a fl exible seal in leaking and non-leaking cracks.