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If the roof needs cleaning, might be best to consider a pro

Sun., Sept. 8, 2013

Q. One side of my asphalt-shingled roof, which is shaded by a large maple tree, has small growths on it that look like the lichens that grow on trees. It also has black stains in other parts of the roof. How can I clean this stuff off and what is it?

A. The growths that look like lichens probably are lichens, which can grow on asphalt shingles as well as trees. The black stains are a fungus. Shingle stains like these are very common, especially in areas of high humidity and on roofs shaded by trees.

Unfortunately, cleaning a roof isn’t easy and it is usually not a good do-it-yourself project, mainly because roof work is dangerous, especially on wet, slippery surfaces. The only way for a do-it-yourselfer to work on a roof with reasonable safety is to wear an approved safety harness, which can cost $50 or more, and attach the harness to an appropriate restraining system (not a length of clothesline looped around a tree).

Safety equipment for roof cleaning should also include safety glasses, gloves, long sleeves and long trousers. Ladders must also be set up and used according to safety rules.

Many mixtures for roof cleaning are available at home centers and on the Internet, but care should be used in selecting one. Some cleaners contain bleach, either chlorine or oxygen bleach, and some experts say bleach should be left on asphalt shingles no more than five minutes or it will damage the shingles. Other cleaners contain sodium hydroxide, which is the chemical name for lye or caustic soda, a powerful chemical that can be hazardous if not used properly. Many roof cleaners can also damage plants unless the plants are thoroughly soaked before and after use.

For all these reasons, it pays to hire professionals to clean roofs, but it is sometimes difficult to find a pro that uses safe cleaning methods. Many roofers won’t clean roofs, and some who do want to use pressure washing, which can damage the shingles if the water pressure is too great. Garden-type sprayers are usually used to apply cleaners, and most experts recommend rinsing with a hose equipped with a nozzle that delivers a forceful stream of water. If you are successful in finding a roof-cleaner pro in your area, find out what method of cleaning is used and make sure it is safe for your roof and plants before signing a contract. The roof cleaner should also have liability insurance and worker’s compensation for employees.

Q. A chunk broke off the side of my concrete driveway, and I tried to patch it with a good quality patching cement. The patch looked fine for a while, but broke off at the same point where the original had broken. How can I make the patch stick?

A. The best bet is to use a concrete bonder to help hold the patch in place. Bonders are liquids that are usually applied to the broken area with a paint brush but can also be mixed with the patching mixture. Bonders can be bought in containers of various sizes at most home centers, hardware stores, or on the Internet. Elmer’s and Sakrete are two well-known brands.

An alternative method is to drive several concrete nails part way into the broken surface, letting the nails protrude an inch or more. The nails grip the patch and help hold it in place. Concrete nails are very thick, strong nails that won’t bend if driven properly. It doesn’t matter if a few nails get bent, as long as they protrude enough to help grip the patch.

Questions and comments should be emailed to Gene Austin at Send regular mail for Gene Austin to 1730 Blue Bell Pike, Blue Bell, PA 19422.

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