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posted: 6/23/2013 4:00 AM

Multiple options available to clean algae and other stains

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Q. The question I have relates to having my roof shingles replaced in 2003 with gray, 25-year Owens Corning fiberglass/asphalt shingles. As time has gone on, the shingles have turned black where they don't get a good exposure to the sun, and seem to have leached a black residue that has run down and discolored the white, aluminum-clad fascia.

From your earlier columns, I believe if I had a zinc strip installed across the peak of the roof, it would do away with the black fungus, or whatever it is. However, can you tell me what would be a good way to clean up the badly stained fascia? Is there a solution that would remove the stain without damaging the aluminum under the white paint? I assume the stain comes from the asphalt and wonder if a solvent for asphalt is what is needed.

Finally, I realize my vinyl-clad siding needs cleaning, and I'm thinking a pressure wash is probably in order. I have a two-story colonial house with a two-car, single-story garage and a single-story addition. I assume it is important to select an experienced pressure-washer vendor, and I have no idea of what to expect in the way of cost. Can you provide any suggestions and/or insight regarding who to select and what to expect to pay?

I apologize for the lengthy message, but will greatly appreciate any response you are able to provide.

A. Your shingles are stained with algae, which develops in areas of roofs that do not dry quickly following rain or dew. It's a very common problem, which seems to have become worse in the last decade.

There are several products available on the market to remove the algae stains. Stainhandler ( sells a Roof & Deck Cleaner, which uses sodium hydroxide and claims to work quickly. Wet & Forget may be more environmentally benign, but may take as long as a year to remove the stains. It is also supposed to kill lichen and moss over time, but it will not remove the growth; weather and time will eventually dislodge the dead blooms.

The old standby method is to use a mixture of equal parts fresh Clorox bleach and water, and spray the roof with it on a windless day. One gallon of the mixture will treat 50 square feet. Do not overspray; avoid runoff. Soak vegetation and cover it before spraying the roof, and rinse it thoroughly when done. If you have metal gutters, keep water running through them while the mixture drips into them.

Installing zinc strips, also sold by Stainhandler, is the long-term solution, as it will continue to leach ions that kill all these nefarious growths. Zinc rolls are also available in building supply houses.

The stain on the white aluminum fascia is likely not from the roof algae; it is another environmental pollution. You should be able to clean the stained aluminum using paint thinner or any strong commercial cleaner such as Simple Green, etc.

Pressure washing can clean vinyl siding and the aluminum fascia. An experienced pressure-washing contractor may also clean the roof, but I would not recommend pressure washing the shingles, as it can dislodge the mineral granules that protect the asphalt from UV degradation. Roof cleaning must be done gently.

I would recommend that you select an experienced pressure-washing specialist. Ask for references and call them to get feedback from these former clients. You should ask for estimates, but don't just go for the lower price -- this is sometimes the worst thing you can do. Far more important is how long someone has been in business, the insurance the contractor carries to protect his or her workers and you, the level of satisfaction from past customers and the follow-up in case of claims.

Q. I have a 25- to 30-year-old colonial with a small front porch that is a concrete slab. I would like to make it look a little nicer. It is nice and level and usable. I have been reading a little about overlays. I don't want to do anything drastic and change the height of the slab that much or redo the porch railing, etc. Any ideas? And whom would I call?

A. There are several companies that offer products for concrete overlays. Here are two websites, where you can see their products and decide which you like: and Then click on the boxes asking either for a ZIP code or "where to find a contractor" trained to install their product.

You can also call local concrete contractors and ask them if they do overlays. I know one who has done all my concrete work since 1970, including beautiful exposed aggregate, and who does overlays.

Q. We live in a house constructed in 1939.

• We have an asphalt driveway on the north side of our house that goes down a slope from the street to our backyard. It does not go to a garage and is not used for parking vehicles at this time. Over the past several years, a lot of moss has grown on the asphalt. At some places it covers almost half of the width of the driveway. Other than eliminating the slippery surface, are there other reasons for getting rid of the moss?

• Over 20 years ago, we removed the rain gutters from the front of our house. That was the only section that had them. The front has a very steeply pitched roof and the water runs onto a flat surface along the front foundation. What is your recommendation on rain gutters?

• We have grapevines growing on the back of our house on stucco. It does not seem to be harming the stucco. We do keep it off the wood trim. Is there a reason to take the vines off the house?

A. Eliminating the slippery condition is reason enough to get rid of the moss, which can be done by scraping it off with a square-end shovel or floor scraper. If left on the driveway, water may be drawn into it by its roots, which may eventually cause some deterioration when freezing. Round Up or similar herbicide may also be used to kill the moss down to the roots.

Gutters in Vermont's climate may be a source of maintenance problems and lead to leakage inside the house as they fill with ice. They can be useful if the house is so well insulated that there is never any ice forming at the eaves, but otherwise there are other ways of handling roof water. One of my favorite ones is the installation of the Rain Handler (, a series of louver-like fins that disperse roof water instead of dumping it straight down where it can dig a trench in the grade, which may lead to foundation leakage.

Another way is to lay masonry units flush with a slightly sloping ground at the drip line of the roof to prevent erosion.

If the grapevine has not caused any damage to the stucco, leave it there, but keep an eye on it. A good time for such a survey is when the leaves have fallen in the fall.

Q. I have been actively planning to replace my windows and siding this year. Your April 20 column has altered my plan to also add one inch of XPS. After some discussions with contractors, I have questions.

My house is a two-story colonial. It was built in 1983-84. It is two-by-four construction. I did add 3/4-inch "Thermax" on the interior walls when I built it. The OSB sheathing was covered with Tyvek, and the siding was spruce clapboards.

• Can the XPS be nailed directly to the OSB board? This would be good, as it would mean that the standard 2-by-6 jamb thickness of 6 9/16 inches could be used for the new windows. I have wondered if a quarter-inch space should be left between the XPS and the OSB board.

• One contractor suggested that he would recommend ripping off the old Tyvek and installing new house wrap (perhaps not Tyvek?) over the XPS.

• I don't see the reason to rip off the old Tyvek. Do you?

• Do you think it would be sufficient to tape the seams in the XPS and forget the new house wrap?

• While researching on the Internet I found a "guide to insulating sheathing." It shows various cross-sections of walls, and indicates that "house wrap" between the XPS and sheathing would provide a "drainage plane." This could suggest that it might be a good idea to apply new house wrap before applying the XPS since the existing Tyvek has literally thousands of holes from the nails for the old siding.

• What method should be used to attach the XPS?

I am hoping you can help with some answers for me and, I think, for many contractors. The questions involving water and water-vapor treatments on exterior walls are difficult to answer since they are not properly understood.

A. The XPS can be tacked lightly over the existing Tyvek and the OSB (oriented strand board) sheathing. The quarter-inch space is best provided between the XPS (extruded polystyrene) and the clapboard as a rain screen. This can easily be accomplished by tacking Benjamin Obdyke Home Slicker over the XPS. If the joints of the XPS are taped with a compatible tape (not duct tape), there is no need for another housewrap. The clapboards will need to be nailed with nails long enough to go through the XPS, the OSB and penetrate 5/8 to three-quarters of an inch into the studs.

Regular house wrap does not provide an effective drainage plane, but there are house wraps that are designed to do so. A double layer of regular housewrap also works, but you are better off using Home Slicker.

I would strongly suggest that you choose a contractor who is already experienced in such an application, as it is important that each of these steps be carried out as intended. For instance, the Home Slicker must be screened top and bottom to prevent insect intrusion, and ventilation must also be provided at the top, or part of the ventilation system is negated.

• Henri de Marne was a remodeling contractor in Washington, D.C., for many years, and is now a consultant. Write to him in care of the Daily Herald, P.O. Box 280, Arlington Heights, IL 60006, or via email at

2013, United Feature Syndicate Inc.

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