How do you seal a leaking roof?
Short answer. Sealing works only for small, specific openings: exposed nail heads, a gap where counterflashing meets brick, the top of a pipe boot collar, or a lifted shingle tab. Clean and dry the spot, use a sealant made for roofing such as asphalt roof cement or a polyurethane or hybrid sealant, and treat it as maintenance, because it will not fix rusted flashing, torn shingles or a worn-out roof.
Where sealant belongs
- Exposed nail heads on ridge caps, vents and flashing.
- Counterflashing joints at a chimney or wall reglet.
- Lifted shingle tabs, as dabs under the tab rather than a smear on top.
- Small gaps between a pipe and its boot collar, as a short-term stopgap.
Where it does not belong
- As the only thing between water and the house at a wall, chimney or skylight. Sealant shrinks and cracks in the Georgia sun within a few seasons.
- Smeared over cracked or hail-damaged shingles, where it hides damage and holds water against the mat.
- Across valleys, where it blocks the flow and creates dams.
How to apply it so it lasts
- Pick a day when the surface has been dry for several hours.
- Clean off dirt, loose granules, old cracked caulk and pine pollen with a wire brush.
- Choose the right product: asphalt roof cement for shingle work, polyurethane or hybrid polymer sealants for metal and masonry joints, and products labeled for your coating on metal roofs.
- Tool the bead so it bonds to both surfaces, and keep it thin enough to cure fully.
- Recheck it every year or two; sealant is a maintenance item.
If you are sealing the same spot every year, the part under it has failed. See roof flashing explained and pipe boot leaks.