Waterproofing Membrane - Water Guard 491 Water Guard 491 is a two-component polymer modified highly flexible cementitious product. It is an eco-friendly waterproof coating for the protection of concrete and mortar. It provides excellent adhesion, flexibility, crack bridging ability and durability. Water Guard 491 can be applied to various cementitious surfaces in marine structures, basement waterproofing, bathrooms, wet area waterproofing, swimming pools, roof waterproofing and water tanks, respectively. Water Guard 491 is also suitable for potable water retaining structures and drainage culverts.