What black sealant should you use on roof flashing?
Short answer. For flashing on asphalt shingle roofs, the usual black products are asphalt plastic roof cement, which is troweled on, and asphalt or rubberized roof sealant in caulk tubes, both of which bond to shingles and metal. For a longer-lasting joint at counterflashing or metal laps, a black polyurethane or hybrid polymer sealant rated for roofing holds up better to Georgia sun and movement.
The main types
- Asphalt plastic roof cement: thick, black and troweled. Good for sealing under shingle tabs, bedding flashing edges and patching small holes. Look for products that meet ASTM D4586. It hardens and cracks over time in direct sun.
- Asphalt or rubberized sealant in tubes: easier to apply neatly at nail heads and flashing edges, and some versions tolerate damp surfaces.
- Polyurethane sealant: strong adhesion to metal and masonry, flexible and paintable, a good choice for counterflashing reglets.
- Hybrid polymer sealant: bonds to many surfaces, resists UV, and stays flexible.
- Silicone: excellent UV resistance and common on metal roofs, but it bonds poorly to asphalt and nothing else sticks to it later.
- Butyl tape: goes inside metal laps, not on the surface.
Why black?
Black blends in with dark shingles and hides dirt. Color does not change performance, but it matters at a front chimney where a gray or white bead would stand out.
Application tips
- Remove old cracked sealant, rust and grit first.
- Apply to dry metal, and avoid metal so hot from midday sun that the sealant skins before it bonds.
- Do not put silicone over old asphalt sealant; it will not bond.
- Recheck sealant joints every year or two.
Sealant supports flashing; it should never be the flashing. See roof flashing explained and chimney leaks and crickets.