ChimneySaver Water-Base Water Repellent is a penetrating, V.O.C. compliant, water repellent which contains a proprietary modified siloxane. This water-based siloxane penetrates masonry up to 1/4 inch or more depending on surface porosity and moisture content at the time of application. ChimneySaver Water-Base Water Repellent reacts with the minerals in masonry in the presence of ultraviolet light and atmospheric moisture. This reaction forms strong permanent bonds beneath the surface and creates a hydrophobic zone that prevents water molecules from penetrating, while allowing free migration of water vapors. The chemical bonds formed in this process allow ChimneySaver Water-Base Water Repellent to become an integral part of the substrate and provide long term water repellent protection.