Asphalt Roof Cleaning And Stain Prevention









My wife and I were returning from a week long trip about 6 years ago. She happened to notice the roof. “What are those ugly black streaks on our roof?” she asked. “Can you do something about that or should we have our roof replaced?” Since our roof was only about 8 years old at the time, I hoped there was a way to safely clean it.

Roof Attack?

It’s funny how neither one of us had noticed those horrible looking black streaks that had seemingly appeared during the week we were gone and attacked our roof. If these same stains were on our cedar siding we would not have put up with them for a moment. I soon noticed that it was not just our home that was plagued. Most of the homes in our neighborhood also had these ugly black stains on their roofs. While on my travels I noticed this problem was common almost everywhere.

Ask a Chemist

Having become keenly aware of the problem, I wanted to know all I could and find the best solution to safely remove those stains from our roof. I asked our chemists at SaverSystems to start working on a solution that was safe to use, safe for the roof, and the surrounding vegetation. I owned a small house next to our plant with a white roof that had turned black on the north side. This roof became our test lab.

What’s The Right Chemistry?

After some initial research we discovered that there are essentially two types of chemistry currently being used to clean roofs- Chlorine Bleach and Sodium Hydroxide. Each had its advantages and disadvantages. Every summer for six years we tested every commercially available product we could find that was made with bleach or sodium hydroxide, including our own experimental formulas. We recorded the results and watched the test areas for several years to see how quickly the stains would return.

Hundreds Of Experiments Later…

After performing hundreds of experiments, we developed two products. The first is an effective cleaner that’s safer than chlorine bleach and sodium hydroxide and is not harmful to the roof or surrounding plants. The second is a stain blocker that helps prevent stains from returning. Simply apply this product after cleaning and re-treat about every two years or at the first sign of the stains returning to block further staining.

Best Roof Cleaning System

We then consulted with experienced roof cleaning contractors and cleaned dozens of roofs to develop the best methods and tools for effective roof cleaning. We developed what we feel is the best and most effective roof cleaning system available.

 Roof Stains 101

 The Great Algae Migration

The most common culprit causing these unsightly stains on asphalt roofs is a blue-green algae called Gloeocapsa Magma. Over the past 25 years this strain of algae has become hardier and has migrated to less humid environments. It has now become a common sight on asphalt roofs across 80% of the United States. The unsightly growth usually occurs on the north or west side as well as shaded areas of the roof. As the algae grows and decomposes, it holds moisture, which accelerates its growth.

A Change For The Better?

Another factor contributing to the growth of this problem is the change that occurred about 30 years ago in the way asphalt shingles were manufactured. In the early 70’s manufacturers began using a fiberglass mat. Previously they used an organic mat made of felt or other organic base composed of various cellulose fibers. The mats are saturated with an asphalt coating and surfaced with weather resistant mineral granules.

With the use of fiberglass mats, and higher oil prices, came the use of calcium carbonate (finely crushed limestone or marble dust). It was added to the asphalt coating as a filler or extender.Algae’s Favorite Snack Food

Unfortunately, limestone is a favorite food source for this strain of algae. Do you have any buildings made of limestone in your town? If they’ve not been recently cleaned, you will likely see black stains caused by this same algae on the limestone. Often, these black or dark brown stains are mistakenly thought to be dirt, tree droppings, mold, fungus or mildew. Actually they are caused when the algae begins to decompose.

Algae growth on roofs occurs to varying degrees in all regions of the country, especially those subjected to warm humid conditions. Nearly all types of roofing are susceptible to staining and discoloration. It is, of course, most visible on lighter colored roofs and less visible on darker shades of roofing.

There are other types of fungi and algae that can cause staining, like green stains sometimes seen on roofs. However 99% of roof stains are caused by Gloeocapsa Magma. In some parts of the U.S., moss build up is a problem as well.

Your Stained Roof Can Look New Again, Last Longer, And Save You Energy Cost

There are three major problems associated with biological attack on asphalt roofs- appearance, shortened roof life, and increased energy cost. Algae and fungi growth on roofs may also contribute to allergies.

Is Your Roof An Eyesore?

Roof stains caused by algae attack start out as areas of light discoloration then turn to unsightly black or dark brown streaks. If not stopped, the entire roof will become an even worse eyesore as the algae continues to grow and deteriorate. These ugly roof stains detract from your home’s curb appeal, pride of ownership, and may affect its resale value. Realtors almost always recommend removing these unsightly stains from your roof before listing your home for sale.

A Clean Roof Will Last Longer

Biological attack from algae can cause damage to your shingles and shorten the life of your asphalt roof. The algae take root on the surface of your shingles helping to dislodge the protective granules. Surface temperatures are also increased because of the dark stains. Its growth holds water on the roof’s surface which also intensifies the sun’s ultra violet rays like a magnifying glass. The increased moisture and UV rays work to further dislodge the protective granules and attack the shingle’s protective asphalt coating. Moisture, UV rays, and thermal movement from temperature extremes are your roof’s greatest enemies. All three are intensified by algae growth. It can suck the life from your asphalt roof leading to earlier than necessary roof replacement.

Keeping Your Roof In The Dark Can Increase Your Energy Costs

Roofs darkened by algae growth can increase cooling cost by as much as several hundred dollars a year. Measuring the surface temperature of dark, algae stained areas, versus unstained areas on the same roof, reveal that surface temperatures are increased by as much as 10%. In parts of the country where the cooling season is equal to or longer than the heating season, lighter shades of asphalt roofs are often used to lower cooling costs. More energy is needed to cool your home as roofs grow darker from biological attack.

Is There An Un-Healthy Fungus Among Us?

Algae and most other forms of fungi reproduce from tiny airborne spores. Like most plants, these spores will grow wherever they find minerals, moisture, warmth and light. Having an algae garden on your roof spewing off millions of microscopic spores around your home is not ideal, especially if you or a loved one suffers from allergies.

Roof Cleaning 101

The past five years we have seen a growing number of companies offering roof cleaning services. There are two distinct schools of thought among roof cleaning professionals. Each camp holds strong opinions as to what is the best product and method to clean asphalt roofs.

The Product Debate

Which to use? Chlorine bleach based cleaners or non-chlorine bleach cleaners made from sodium hydroxide (lye)? Lye is the main ingredient used in many paint strippers and drain cleaners. Both products and the methods used to apply and rinse them have their pros and cons.

Chlorine Bleach

Discolorations from algae and biological growth are difficult to remove from roofing surfaces.

Bleach will lighten the stains to the point they will not be visible. However, bleach will not fully remove the algae colony or its root system. Because of this, stains will typically return sooner on roofing cleaned with bleach than with some other products. In extreme cases, algae stains have returned in as little as 6 months.

Bleach solutions rinsed from the roof into the ground can kill surrounding vegetation. It will also neutralize many chemicals used for termite protection and may void your home’s termite warranty.

Bleach can accelerate corrosion of metal gutters, downspouts, flashings, and roofing fasteners. It may also fade or dull the color of the roof.

Besides the obvious health risks of handling chlorine bleaches, strong bleach solutions will damage almost any hard surface that comes in contact with it. Asphalt shingles are no exception.

Sodium Hydroxide

Sodium Hydroxide (lye) is the active ingredient found in many paint strippers, oven cleaners, and drain cleaners. It is caustic and care should be used to follow all cautions on the label. However, these solutions when rinsed from the roof into the ground, are somewhat safer than bleach for surrounding vegetation.

Sodium Hydroxide is an effective degreaser and high concentrations may cause irreversible damage to asphalt shingle roofs.

Sodium Hydroxide-based products are generally more effective at removing algae colonies, but require more dwell time and are harder to rinse from the roof surface than chorine bleach. Effective rinsing often requires the use of high pressure washing systems.

Pressure Washing

Some roof cleaning companies will use a pressure washer to speed the rinsing process. Even though they claim to turn down the pressure, use a wide tip, and hold the tip higher above the surface to avoid damage, they are still blasting the surface with 200-300psi of water pressure.

Asphalt shingles are not designed to withstand even that much, so-called low pressure, and permanent damage may result. A good stiff rinse is needed to remove algae colonies and their root systems, but it’s best to avoid the use of power washers.

Safer, More Effective Roof Cleaning

DEFY Roof Cleaner is the first effective roof cleaning product that does not rely on harsh chemicals like chorine bleach or sodium hydroxide. It strikes a perfect balance between aggressive cleaning and not being harmful to the roof or surrounding vegetation. It’s made of an optimized blend of detergents, coupled with a unique buffered Sodium Metasilicate—a chemical, made from sand and soda ash, which is recognized as a non-pollutant.

How the System Works

DEFY Roof Cleaner breaks up the masses of algae rooted to the shingles surface into very fine particles. Then, a specially developed rinsing tool is used to remove the algae from the surface. The rinsing tool, attached to a garden hose, will remove the algae spores and any remaining roots more effectively than just rinsing with a garden hose. This is no more harmful to the roof than a hard driving rain. This means roofs stay cleaner longer, and no damaging pressure washing is needed.

Stain Prevention & Maintenance

DEFY Stain Blocker protects the roof and helps prevent stains from returning. Once the roof has been properly cleaned and rinsed, it should be treated with Defy Stain Blocker. Maintenance coats should be re-applied about every 2-3 years.

The frequency of maintenance coats will depend on many factors. Climate, orientation of the roof, and surrounding trees that keep direct sun off the roof are just a few of the factors that determine when a maintenance coat will be needed. In extreme cases, maintenance coats may need to be applied yearly. In ideal situations, maintenance coats may only be needed once every five years.

It’s best to treat each roof on a regular maintenance schedule or at the first sign of staining. The bottom line is the more humid the climate the faster stains will return. In the Southeast new asphalt roofs can turn black in less than 2 years. While in the Midwest it may take 5-8 years before stains become an eyesore on a new asphalt roof.

Tools Of The Trade

Like any job it’s always easier with the correct tools and equipment. Here is what we recommend to do this work in the best and most efficient manner.

DEFY Roof Cleaner Concentrate– one gallon of concentrate makes about 7 gallons of finished product. Coverage per one gallon of concentrate is about 700-900 square feet. Sold in cases of 4/1 gallons.

DEFY Stain Blocker for Roofs– Apply after cleaning. Use to form an invisible shield that blocks stains from returning. Maintenance coats should be applied about every two years or at the first signs of stains return. Coverage is approximately 250 sq. ft. per gallon. Sold in cases of 4/1 gallons and 5 gallon containers.

Roof Cleaner Applicator– Use this to apply the cleaner, simply pour the concentrated cleaner into the applicators reservoir. Set the dilution dial to “C” (1:6), attach it to the hose, and spray on roof. This saves time and eliminates the need for mixing.

Roof Rinsing Tool– A safe, low pressure rinsing system made exclusively for SaverSystems by American Water Broom. The 3 head rinsing tool attaches directly to your hose. It safely removes the algae colonies and their roots without harming shingles.

Water Hose– a minimum of 150 feet of 3/4″ diameter heavy duty contractor hose is best. Smaller hose diameters like 1/2″ or 5/8″ will reduce cleaning efficiencies when rinsing.

Ball Valve– Use a 3/4″ ball valve on the hose end. This will allow you to easily shut off water flow to change from cleaner applicator to rinsing tool. Note: Make sure the valve you choose does not restrict water flow.

Pump-up Sprayer– You will need a hand-held pump up sprayer for applying Stain Blocker. A sprayer with a large 2-3 gallon tank works well and saves refilling time.

Other Helpful Tools

These additional items will save you time, potential problems and increase your safety.

Electric Utility Pump– A 1/2 hp or slightly bigger utility pump rated for a minimum 20 gpm. Available at most farm supply and home improvement stores. Note: A minimum of 80psi of water pressure is best for rinsing. A small pump is helpful because water pressures will vary greatly from each location or municipality. Additionally, pressure is lost from the rise in the hose when rinsing on roofs.

4″ Plastic Drain Pipe– It’s good to have several 8′-12′ sections of flexible drain pipe. Attach to downspouts to redirect run off of cleaner and rinse water. If down spouts drain into flower beds or near expensive ornamental plants, it’s best to direct run-off away from these areas.

Roofing Boots– Water resistant boots made especially for walking on roofs. These boots made with special replaceable pads are designed for maximum grip on roofs.

A Basic Overview of Safe and Effective Roof Cleaning Procedures

Step 1 Roof Inspection. Before cleaning, inspect the roof and repair any minor trouble spots. Replace or repair any weathered roof boots or flashings. Re-set nails and re-caulk any areas as needed. Check gutters and down spouts and remove any blockages that may cause gutter over flow.

Step 2 Protect Surrounding Areas. Move or protect any non-target objects that might be subject to overspray. Move any automobiles from drive or out of range of overspray.

Step 3 Fall Protection And Safety. Roofs can become slick and hazardous when wet and especially so when cleaner is applied. The use of OSHA approved fall protection devices is recommended. Consult your safety equipment supplier. Use extreme caution when working with water hoses and rinsing tool around power lines near roofs.

Step 4 Apply Cleaner. Apply cleaner according to label directions with Roof Cleaner Applicator.

Step 5 Rinse. For best results use Roof Rinsing Tool according to rinsing instructions on the Roof Cleaner label. Use of a small utility pump connected between two sections of hose can be helpful if more pressure is needed.

Step 6 Apply Stain Blocker. Apply stain blocker according to label instructions to help prevent the stains from returning. As a general rule this will prevent stains from returning twice as long as a roof that was cleaned and not protected. Results will vary depending on type, condition of roof, and climate.

Helpful Tips

  • Severely stained areas may require repeat applications or higher concentrations of roof cleaner.
  • Avoid gutter over flow.
  • Avoid wind drift to adjacent property when spraying roof cleaner and stain blocker.
  • Rinse roof surface until rinse water is clean.
  • Zinc strips can be installed for additional protection.


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