Water Stopping Cement An instant-setting hydraulic cement formulation especially made to patch and repair difficult leakage areas. Wet-Plug will actually stop the flow of pressure leaks that occur in masonry surfaces. Flowing water can be stopped instantly…just mix with cold water and hold in place until leak is plugged. Sets in 3 to 5 minutes; surface may be smoothed, trimmed and decorated within 1/2 hour! Wet-plug works wonderfully for interior or exterior use.