Hardcast Spray Seal, 5 Gal. Spray-Seal is an all-purpose high performance sprayable sealant for use on all types of metal duct, ?berglass duct board, duct fabric and ?ex duct. Distinguished by its ability to accommodate minor vibration and movement, Spray-Seal stays ?exible and will not crack. Spray-Seal decreases labor substantially and increases productivity while using less material. 10 Year Outdoor Warranty when combined with an AFT-701 combination system.