Kool Flex Mastic

Kool Flex Mastic is a professional-grade, high-solids, moisture-cure silicone mastic engineered for superior flexibility, adhesion, and long-term performance. Designed for critical repair and sealing applications, this 100% silicone formula is ideal for use on roofs, flashings, walls, masonry, and metal seams and fasteners — even in wet or underwater conditions. Formulated to deliver exceptional durability in extreme environments, Kool Flex Mastic becomes rain-safe in just 1 hour and remains permanently flexible without cracking or hardening. It bonds tenaciously to most common substrates including EPDM, concrete, metal, aged coatings, Kynar®-finished surfaces, and polyurethane foam — without the need for primer in many cases.