Renderoc Plug is a rapid-setting, cement-based mortar from Fosroc used for quickly stopping active water leaks in concrete and masonry structures. It is a single-component, pre-bagged powder that is mixed with water on-site and is designed for emergency repairs in areas like tunnels, basements, and sewage systems. There are different grades, such as Renderoc Plug 1, which sets in about one minute, and Renderoc Plug 20, which sets in approximately 20 minutes.