Home Improvement
LEAD: SO-CALLED flat roofs, which almost always slope slightly to facilitate drainage, should be inspected about twice a year. Routine maintenance and minor repairs usually can be done easily by amateurs, but widespread or major damage should be handled promptly by a licensed roofer.
SO-CALLED flat roofs, which almost always slope slightly to facilitate drainage, should be inspected about twice a year. Routine maintenance and minor repairs usually can be done easily by amateurs, but widespread or major damage should be handled promptly by a licensed roofer.
Most flat roofs on houses and commercial buildings are built up with several layers of roofing felt and either coal tar or asphalt. Both types may be covered with a layer of gravel or marble chips to protect the surface and reflect heat.
A roof that is not covered with chips may not be strong enough to support their weight; do not add chips without consulting a building inspector or roofing engineer.
Such roofs should be maintained by applying liquid roof coating every two or three years.
Roof coating seals and protects the layers and fills small surface cracks. It is available in five-gallon cans from hardware stores and home centers and is applied with a disposable push broom made for the purpose.
There are two types of roof coating: black and metallic. Although both contain asphalt, the black coating generally contains more and therefore has greater waterproofing ability. The metallic coating contains aluminum to reflect heat.
Apply roof coating during dry, warm weather. (During hot weather, when the roofing is soft, walking on it can cause damage.) Wear old clothes, shoes and gloves; you won't be able to clean them. To transport a container of coating to the roof, use a hoist, or have an assistant on the roof to take the container from you before you step off the ladder.
First, make any needed spot repairs (described in detail below), then sweep the roof free of loose material. Stir the coating thoroughly with a stick, then dip the broom, and begin spreading the material. Start at the point farthest from the ladder so you can coat the entire roof and still climb down.
Spread the coating about an eighth of an inch thick, or as specified by the manufacturer. For best results when applying aluminum roof coating, brush in one direction only, and use a minimum of strokes.
After finishing, dispose of the broom and soiled clothing. Tools and hard, smooth surfaces like gutters can usually be cleaned with mineral spirits. Any unused coating can be stored for up to three years if closed tightly and not allowed to freeze.
Do not rely on roof coating to stop leaks or repair damaged roofing. If the condition is severe, call a licensed roofer, but if the problem is small, like an isolated blister or area of torn roofing, most of the time you can fix it yourself.
If you find a blister in the roofing, first sweep loose material away from the area. Then, using a utility knife, slit the blister open along its length, one layer at a time.
If the interior of the blister is dry, the problem usually is not serious. To fix it, use a putty knife to apply roofing cement (a thick black compound resembling tar) into the blister on each side. Then press the area flat. Drive one-and-a-half-inch-long flat-head roofing nails into the material on each side of the slit at intervals of about an inch. The nails must pierce the roofing and enter the wood decking underneath.
Then spread a layer of roofing cement a quarter of an inch thick over the repair and about three inches beyond it on all sides. Cut a patch of 15-pound roofing felt to fit over the entire area. Fasten the patch with roofing nails spaced no more than three inches apart around the perimeter. Cover the patch and nailheads with additional cement.
Blisters that are wet inside indicate a leak. Squeeze as much moisture as possible from the roofing by standing on the spot, then prop the blister open with a small stick to permit complete drying. Once the area is dry, repair the blister as described above, but to prevent a recurrence, you must also locate and repair the source of the leak - usually torn roofing or parapet flashing, or cracks around roof openings.
To repair torn roofing, first sweep away any loose material. Then, using a straightedge and a utility knife, remove the tear by cutting a square or rectangle around it. On a built-up roof, cut only as deep as the damaged layer. Carefully pry out the cut section, and use it as the pattern for a patch by tracing its shape onto 15-pound roofing felt, or heavier felt thick enough to fill the opening.
Next, cut the patch. Spread roofing cement over the bottom of the opening and around the edges, then press the patch into place, making sure it adheres completely. Nail the patch around the perimeter using roofing nails spaced one to two inches apart.
Cover the patch with additional cement and a second patch that extends at least three inches beyond the first on all sides. Nail this patch to the roof, then cover it with a third layer of cement, followed by gravel or marble chips if appropriate.
To patch parapet flashing, first pry up the metal cap protecting the ridge. Apply roofing cement to the damaged area, then cover it with a layer of new flashing, extending three inches beyond the damage on all sides. Position the upper edge of the new flashing so that the reinstalled metal cap will cover it. Cement a larger piece of new flashing over the first, and reinstall the cap with more cement.
To repair cracked seams around vents, chimneys and other roof openings, apply roofing cement generously to the area.