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Shining some light on algae

January 12, 2006|Nancy Yoshihara

QUESTION: During fall and winter our brick patio on the north side of the house becomes slick and slightly green from moisture without enough sun to keep it dry. Is there something that can be applied to the surface instead of the power wash required each spring?


Los Angeles

ANSWER: Shade and moisture are most conducive to the growth of algae and moss, which can make a brick patio slippery and turn it greenish.

"The easiest cure for algae, if possible, is to eliminate as much of the shade as possible," according to the website Greater sunlight will help eliminate the moisture.

To reduce the slickness in small areas, the website recommends applying a diluted solution of household bleach to patches of algae and moss. If you like the natural effect of the green, Times garden contributor Robert Smaus suggests tossing some sand on the surface to help reduce the slickness.


QUESTION: I have stamped color concrete in my backyard, which was sealed when the work was completed about three years ago. The sealant is now peeling up. Can you recommend a very good sealer, which will adhere and bring back that wet new look that the concrete had a few years ago?

ANSWER: As with anything, maintenance is a big issue, says Graeme Cohen, owner of Concrete LA in Chatsworth.

If you leave a car out in the sun rather than in a garage, the exterior finish on the one without protection will wear worse than the other. The same applies to concrete, Cohen says. Maintenance is a vital part of maintaining the look.

Cohen recommends pressure washing the surface to clear off the peeling sealant, dirt and debris. Then apply a water-based, acrylic or lacquer sealer.

Do-it-yourselfers can find water-based and acrylic sealers at home center stores. Lacquer sealants are not easy to find at these stores, and they are trickier to apply.

Cohen says a homeowner can scrub the surface, but a pressure washer, which can be rented from a home center, is preferable.

When selecting a sealant, read the label to make sure it is recommended for concrete application. An acrylic or lacquer sealer will give that wet look.

Before applying the sealant, make sure the surface is clean, dry and free of standing water.

"The easiest way to apply the sealant is to take a bucket and a roller," Cohen says. "Just roll the sealant over the surface."

Lacquer sealers require special application and care when used around pets, kids and pregnant women. It is a job best left to a professional, says Cohen.

Lacquer will not absorb surface moisture, and trapped moisture will cause the surface to whiten. Application by a professional will cost "probably $1 to $2 a square foot," he said.

Allow all sealants to dry for about 48 hours.

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