Q: I have a brick patio that faces north and gets almost no sun because it is shaded by the deck above. My problem is a dark-green fungus growth that really sticks to the brick. I have found that the only thing that removes this growth is a 1300 PSI power washer, and it does not do a very good job. Can you recommend a cleaner that will take the place of the power washer, and a sealer that will protect the brick from this growth after it has been cleaned?
A: This is a common problem, and we receive a number of similar questions annually, so the information deserves repeating.
Copper sulfate, also known as bluestone or blue vitriol, is a chemical you can use to get rid of moss and algae on masonry (concrete, brick, flagstone, etc.). This chemical can be safely used with minimal damage to grass or garden plants nearby. Copper sulfate is sold at feed stores and some nurseries and is available in powdered and crystal form. The powder is easier to dissolve in water. Mix one pound of it in 20 gallons of water, and spray it over the mossy area. Copper sulfate may seem to be staining the masonry, but the color is easily hosed off.
If brick or concrete remains stained once the moss residue has been removed, you can give it a deep cleaning with dry sal-soda concentrate. Hose the whole area thoroughly, preferably in the evening, and then sprinkle the entire surface uniformly with the dry sal-soda concentrate. Allow it to stand overnight. Then go over the area with a broom or, even better, with a stiff-bristle scrubbing brush (do not use a wire brush because it will leave rust stains). Hose off the area, and repeat as necessary.
If grass grows at the edges of the area you are cleaning, it will be necessary to mop up the wet sludge after scrubbing. Don't hose it off into the grass. Wear rubber gloves when cleaning up the sludge, and protect your eyes from spatters by wearing eye goggles. After removal, flush the area with clear water.
To find sal-soda concentrate, try a chemical supply company or janitorial supply house that handles cleaning chemicals.
Once the masonry is clean, apply a good masonry sealer over the surface for future protection. There are many brands on the market. Check with your local masonry dealer or a well-stocked home center. Look for a penetrating product that reduces biological growth as well as atmospheric soiling and staining.
Because your patio is in continual shade, it is very likely you will experience regrowth of moss during moist weather conditions. This will require additional treatments with blue vitriol and reapplication of a masonry sealer, but shouldn't require the deep-cleaning process with sal-soda concentrate.
Q: My eight-year-old roof is still in excellent condition except for brown streaks that appear to be slowly spreading. I was told it was a mold that could be removed by spraying the roof with a combination of household bleach and water, but this didn't help. It is unsightly since it is the front of the house, and from across the street the roof looks dirty and dingy. Can you help?
A: Excessive moisture, particularly from hot and humid summer weather, as well as too much shading of a rooftop by nearby trees, can contribute to this problem. It is more than a cosmetic problem, because moss and algae growth on a roof can promote decay in the basic structure.
If it is just mildew, regular household bleach will remove the residue (four parts water mixed with one part bleach). This solution should be applied near sundown to let it work without evaporating too soon. Don't rinse.
If the discoloration is green or brown like yours, it is likely that this is more than mildew, but rather a fungus growth. A method of removal I recommend is to scrub the roof with a stiff bristle brush using a solution of 2/3 cup trisodium phosphate (available from paint dealers, not the supermarket product), 1 cup detergent, 1 quart household bleach mixed in 3 quarts water.
Commercial products include Shingle Shield Roof Cleaner (Chicago Metallic, 4849 South Austin Ave., Chicago, Ill. 60638; call 800-638-5192) and Safer's Moss & Algae Killer (Safer Inc., 189 Wells Ave., Newton, Mass. 02159). Both products can be found in home centers and garden-supply stores, or you can write direct to the manufacturer. Follow the manufacturer's directions carefully.
The copper sulfate solution, as described in the preceding question regarding removal of moss and algae from masonry surfaces, is also an excellent treatment for roofs and is another option (not including the sal-soda treatment).
Be sure to use extreme caution when working on a roof. Use solid ladders that are securely anchored, and be aware that the area may be very slippery with algae growth, particularly when wet. Be careful not to damage shingles by stepping on them or scrubbing too hard and disturbing the surface granules that protect the asphalt base of that type of shingle. Before using any of these cleaning solutions, it's best to do a test application on a small area to check for discoloration of the shingles. This would be particularly important on darker surfaces.
Prevent further growth with zinc strips placed on the ridge of the roof line. Rainwater running off the zinc creates fungistatic compounds of zinc oxide that impregnate and cover the roof's surface, thus inhibiting growth of moss, fungus and mildew.
Chicago Metallic Corp. manufactures Shingle Shield, which is a rigid, three-foot, roll-formed section of zinc that is applied continuously along each side of the roof ridge line and additionally below any point that interrupts the flow of rainwater from the ridge line (i.e., chimneys, dormers, etc.). There are other similar products. Check roofing experts in your area.
Send e-mail to firstname.lastname@example.org or write to Here's How, Copley News Service, P.O. Box 120190, San Diego, Calif. 92112-0190. Only questions of general interest can be answered in the column.