EZ-Prime Premium High Build Topside Paint Undercoater should be used as a base coat whenever the surface to be painted is aged, cracked, checked, pitted, or in any way less than smooth. It can be applied to fiberglass, wood and previously painted surfaces. EZ-Prime dries quickly and is easy to sand. This high-build formula has excellent filling properties which can be used for a full, one-coat application. When using on bare wood, seal with 2018 EZ Wood Sealer to provide water resistance and dry rot protection. Not for use below the waterline.