There are many ways to repair leaks in concrete structures like sanitary and storm pipes, manholes and basins. One of the oldest yet least understood methods uses polyurethane chemical grouts that react with water to bond with the concrete to form watertight, permanent seals, or to become rigid, filling voids and stabilizing soil. According to the National Asso-ciation of Sewer Service Companies (NASSCO), chemical grout was developed in 1955. Since then, it has been used in sewers, manholes, tanks, vaults, tunnels, and many other applications worldwide. Recent studies and more than 40 years of experience indicate that grouting — known
