Repairing Asphalt Shingles
The repair will depend on what is wrong with the affected shingles. One truth that applies to all fixes on roofs — more is better. Apply roofing cement liberally. Use as many roofing nails as necessary to secure a shingle. If a shingle is rotted, crumbles, breaks or is otherwise compromised, it is always better to replace it than to repair it. If however, the problem is minor, repairs should abate any more serious hassles.
Tip: All roof fixes are easier in warmer weather, when cement has a better chance to cure. Often it is not reasonable to wait for good weather, but if you can, do.
If a shingle is cracked you may not need to replace it if the crack is only a hairline. Simply slather on roofing cement (or asphalt paint made for this purpose). You can also apply roofing cement sold in cartridges with a caulking gun; it is typically a bit more expensive, but certainly more convenient and easier to tote up a ladder. Make sure the crack is completely filled and slather extra around the crack to form a good seal.
If a shingle is torn slather the area with roofing cement beneath the tear by gently lifting the shingle up only far enough to do the work. Be careful not to pull the shingle free or displace the surrounding shingles. Once you have liberally applied cement, secure the shingle on either side of the tear with roofing nails. Now apply roofing cement generously to the top of the tear and to the nails.
If a shingle is curled, apply roofing cement beneath the curled section and press into place. Secure with roofing nails and cover nail heads liberally with cement.
Tip: Roofing cement can create a mess on your roof and on you. To remove it, scrub your skin, shingle or other affected area with a rag dipped in kerosene. Once done, wash your skin and discard the rag in compliance with local ordinances.