Penetrol Wetting Agent: A clear, air-drying oil displaces air or moisture in rust. USE IT: when multiple tiny rust spots are in the old existing paint and cannot be completely removed, add to the primer; when the metal is extremely hot, or because of gusty winds, your primer and/or finish is drying too quickly; when excessive "air bubbles" appear while applying the finish coat paint, and the bubbles cannot be removed with a dry roller. Assures a long "Wet Edge" during paint application to eliminate laps, brush marks, orange peel, etc.