SEAL-KRETE® HEAVY-DUTY Concrete & Masonry Waterproofer is a water-based, 25% solids, acrylic formula designed to stop water penetration into low density or porous vertical concrete and masonry surfaces such as split-face or fluted concrete block. Heavy-Duty provides a tough, flexible, breathable film which prepares these surfaces for painting. It’s also excellent for binding chalky surfaces on painted or bare vertical substrates including concrete block, tilt-ups, stucco and aluminum siding. It’s unbeatable for strengthening mortar joints. Heavy-Duty lowers surface pH on alkaline substrates and revitalizes the natural colors of surfaces including aged vinyl siding, aluminum siding and stucco.