Sto Watertight Coat is a flexible and breathable waterproofing membrane based on a unique combination of acrylic emulsion, portland cement and fine fibers. Watertight Coat is both flexible and abrasion-resistant. You can use it waterproof all types of above- or below-grade concrete and masonry, including foundations, block walls, balconies,parapets, planter boxes, water tanks and fountains.