What is the best roof repair sealant?
Short answer. There is no single best roof sealant; the best one matches the surfaces and the job. Use asphalt roof cement or a rubberized asphalt sealant on shingles, a polyurethane or hybrid polymer sealant for metal and masonry joints such as counterflashing, a compatible silicone on metal and silicone-coated roofs, and butyl tape inside metal panel laps.
Match the sealant to the job
- Under shingle tabs: asphalt plastic roof cement, applied in dabs.
- Nail heads on shingles, vents and boots: asphalt or rubberized roof sealant in tubes, or a hybrid polymer.
- Counterflashing in brick or stone: polyurethane or hybrid polymer rated for masonry.
- Metal roof fasteners and trim: a sealant rated for metal roofing and compatible with the panel finish.
- Metal panel laps: butyl tape between the panels, not caulk on the outside.
- Silicone-coated roofs: only silicone bonds to silicone.
- Emergency patches in the rain: products labeled for wet application, as a temporary measure only.
What to look for on the label
- Rated for roofing and for your specific surfaces.
- UV resistance for exposed joints.
- Movement capability, which matters on metal that expands in Georgia heat.
- Service temperature range.
- Whether it can be painted, if appearance matters.
Mistakes that shorten sealant life
- Applying over dirt, pine pollen or old cracked sealant.
- Gobbing it on instead of tooling a bead that bonds to both sides.
- Putting silicone over asphalt products, or asphalt over silicone.
- Using sealant where a piece of flashing is actually needed.
Even the best sealant is a maintenance item to recheck every year or two. See roof flashing explained and the roof maintenance checklist.