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Best Sealants & Coatings for Flat Roofs
Mastic, silicone, and liquid rubber all have a place — the right one depends on your roof, the weather, and what you’re actually trying to fix.
Black Mastic
A go-to for ahead-of-weather repairs — often recommended when rain or humidity is in the forecast. Works well with fabric reinforcement for anything beyond a pinhole, applied at roughly an eighth-inch in the middle and feathered thin at the edges so it doesn’t peel up later.
Silicone Coatings
Silicone systems handle ponding water and UV exposure well over the long term, which makes them a strong choice for roofs with a recurring drainage issue that can’t be fully corrected right away, or for extending the service life of an otherwise sound membrane.
Liquid Rubber
Offers flexibility across temperature swings, which suits roofs that see real seasonal variation. Often used for smaller, targeted repairs where a fully cured, monolithic seal matters more than large-area coverage.
Frequently Asked Questions
Can I just use whichever sealant is at the hardware store?
You can, but not all products are formulated for roofing use or compatible with what’s already on your roof. The wrong product can fail faster than a proper roofing-grade system.