MasonryDefender Penetrating Chimney Brick Sealer is an commercial grade, siloxane water repellent that bonds with the minerals in all porous, exterior masonry surfaces to provide long-lasting water repellency. MasonryDefender Chimney Brick Sealer is a breathable, non-film forming, brick sealer that will not alter surface color or appearance. MasonryDefender Chimney Brick Sealer protects most horizontal, exterior, above-grade masonry surfaces. Product is suitable for use on residential chimneys, brick walls, masonry structures, or most other vertical, masonry substrates including stone, brick, stucco, granite, limestone, as well as cultured stone. Natural substrate color and surface textures are unaffected with little or no gloss created. Slight darkening may occur on dense surfaces. Testing is recommended before treating any surface to ensure desired results. This product is designed to protect brick chimneys, brick walls, and brick houses once they have been properly cleaned with MasonryDefender All Purpose Masonry & Concrete Cleaner.