Old 02-20-05, 01:57 PM
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How does one clean that green stuff called alae off of a cement patio . There are weeds around the patio so i believe thats where they came from along with
the gutters filled with roof moss.
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Old 02-27-05, 06:10 PM
howiek's Avatar
Join Date: Sep 2001
Location: Acton, Ontario, Canada - Zone 6b
Posts: 413
Hello Rafeal

Is the patio always shady and damp?

Is it moss or algae?

You could try to clean off the patio with a bleach solution, but you'll probably need to work it over the affected area(s) with a stiff broom or brush. Also, you will have to be very careful not to allow any runoff onto gardens or turf as the bleach will also kill your garden plants or grass.

Is there any way to increase sunlight or at least get better air circulation over the affected area? Creating a dryer atmosphere should also help discourage algae or moss.

You could also check local nurseries or garden centres to see if they have a product specifically used to target the problem area. You could also try your local County Extension or County Agent

Also, where do you live? This may or may not affect method of treatment.

Good luck with your problem

Hopefully others can offer a solution

Old 03-02-05, 12:38 AM
Join Date: Aug 2000
Location: USA
Posts: 15,834
Algae thrive on alkalinity. Algae live in colonies. Algae are usually green in color but can also be a bluish gray & sometimes black during low humidity. Algae create ideal conditions for mold, mildew and moss growth. Algae also form an extremely slippery surface on concrete, masonry & wood walking areas.

Once concrete is thoroughly clean, seal with concrete sealer to reduce the reactivity with the alkalinity of the concrete. Concrete will have to be periodically resealed. As indicated, if it's possible to get more sunlight into the area. Overhanging branches should be pruned back away from the home. Sometimes it is necessary to thin mature trees to allow more light into the landscape.

Gutters should be cleaned out. It's possible that moss can get into downspouts and clog them. There are commercial moss removers to keep moss and algae from returning. These are best applied when the moss is actively growing. If possible, apply them during a dry spell. Recommended spray materials include copper formulations, copper sulfate, zinc chloride, zinc sulfate monohydrate, and weed-killer compounds which indicate that they are effective on moss. Read and follow label directions.

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