Few things can be more upsetting than the dripping of water from a leak in the roof. Roof leaks typically occur either from a missing or cracked shingle, or from problems around flashings. Fortunately, with a little work and some inexpensive sealant material, you can often cure the problem with a quick and permanent repair, stopping the drip and extending the life of your roof.

The first step is to locate the source of the leak, and that can often be more difficult than making the actual repair. Because water will run down rafters and roof sheathing inside the attic before dripping onto the ceiling below, the spot where you see the water mark may be a long distance from where the leak actually originates. Check the attic and look for water marks on the wood, and try to trace the marks back to the source, or at least to what seems like a logical point of origin. Measure off a fixed point like a chimney or a vent pipe to where you think the leak is coming from.

On the roof, transfer the measurements you took early and inspect the area. Look for shingles that are missing, broken or curled; nails that are missing or protruding up; flashings that are cracked, bent, dented or missing fasteners; or other signs that all is not as it should be on the roof. Once you’ve determined the source, you can decide on the most effective method of sealing things up again.


There are several different types of roofing sealants, and they can be applied in different ways. The one you choose is based on where the leak is, how large the area is that needs to be repaired, and whether the roof is dry.

For most small repairs, such as flashings, fasteners or cracked asphalt shingles, a roof sealant in a 10-ounce caulking tube is the most convenient. The tube is used with a standard caulking gun, and has the advantage of being cleaner and more accurate for smaller applications. If the roofing is damp, be sure to use a sealant that is labeled as wet and dry, which can be used even when it’s raining.

Clean the repair area as best you can. Roof sealants will stick even to dirty surfaces, but if you apply it over a lot of dirt or moss, you won’t get a very effective seal. If there are fasteners that are loose or missing, drive them back down or replace them.

Place the tube in the caulking gun, cut the end of the tube and puncture the inner seal. For loose or curled asphalt shingles, gently lift the shingle with a small pry bar, apply a bead of sealant under the shingle, then use a brick or other weight to hold it down as the sealant sets up.

For cracked asphalt shingles, nail the shingle down with a broad-head roofing nail on each side of the crack, then apply a thin bead of sealant to the crack in the shingle and over each of the nail heads. To help conceal the repair, check inside your gutters for loose granules that may have accumulated there. Collect the granules in a small cup, and sprinkle them over the wet sealant — save any extra granules for future repairs.

For flashing repairs, select a wet/dry roofing cement or a clear caulking formulated for roof repairs. Apply the material with a caulking gun in a thin bead, completely sealing any gaps in the flashing. For flashings that might be subject to movement, use an elastomeric sealant that remains flexible.

For larger repairs, you can purchase roof sealants in quarts and 1-, 3- and 5-gallon containers, in both black and white. Once again, these sealants, also called mastics, are available in dry-application formulas for best adhesion on dry materials, and wet/dry formulas for use on wet surfaces, in rainy weather and even underwater.

The easiest mastic to use is labeled as brushable, which is thin enough to be applied with a brush. Wear disposable gloves to prevent a lot of cleanup on your hands, and apply the material with an inexpensive disposable brush.

For some repairs, brushable sealants are too thin, especially on steep slopes or in hot weather. If that’s the case, look for a roof sealant that is labeled as medium- or heavy-bodied, and apply the material with a trowel. For larger cracks or gaps where there is a danger that the crack may open up again, reinforce the repair with fiberglass tape.

Sealants, mastics, fiberglass tape, trowels, and all the other tools and supplies you might need for your particular repair are available at home centers, hardware stores and any other retailers that sell roofing products. Follow the manufacturer’s instructions carefully for proper application, cleanup and safety precautions, and use all necessary precautions and common sense when working on a roof — especially in the rain!

Remodeling and repair questions? E-mail Paul at paul2887@hughes.net.


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