GacoWash is a concentrated cleaning solution for roof membranes and existing waterproof systems. It is specially formulated to remove pollen, mildew, tough dirt and fungus from roof membranes and existing waterproof systems. GacoWash should always be the first step in every GacoFlex Silicone Roof Coating System. System Of Integrated Products. The GacoFlex Silicone Roof Coating System requires a clean surface. To ensure the roof is completely clean, it is imperative to use GacoWash prior to applying GacoFlex Silicone Coatings.