Hydro Active® Flex LV is a Hydrophobic polyurethane that, when used alone or with Hydro Active® Flex Cat, is designed to form a flexible gasket or plug in joints and cracks in concrete. When it comes into contact with water, the grout expands and depending on temperature and amount of accelerator (Hydro Active® Flex Cat) used quickly cures to a tough flexible, closed-cell foam that is essentially unaffected by corrosive environments.