Flex Seal can be used on roof flashing as a temporary emergency repair to stop an active leak, but it is not recommended as a permanent solution and is not approved by roofing manufacturers or professional roofers for flashing repairs. Flex Seal is a rubberized sealant available as spray, liquid, and tape that can seal small cracks, gaps, and holes in flashing quickly. For a small crack in metal flashing or a gap around a vent pipe boot, spraying or applying Flex Seal may stop water intrusion temporarily. However, there are significant drawbacks for flashing applications. Flex Seal is not designed for the thermal movement that metal flashing experiences, so it can crack, peel, or lose adhesion with temperature fluctuations. It does not provide the mechanical strength and proper water-shedding design of correctly installed step flashing or counter flashing. It can trap moisture underneath and make future permanent repairs more difficult, as roofing cement and new flashing do not adhere well over Flex Seal residue. Shingle manufacturers warn that non-approved coatings can void warranties. For proper flashing repair, the best products are asphalt roofing cement for small sealing and polyurethane sealants like Geocel 2300 for flexible, long-lasting sealing, combined with proper metal flashing installation using step flashing techniques. Use Flex Seal only to stop active interior damage until permanent repair within weeks.
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