Solution percentage for asphalt shingle cleaning

What is the strongest Sodium Hypochlorite percentage recommended when cleaning asphalt shingles? My wife and I want to start a business cleaning roof stains.

John Stout with Go Roof Tune Up™ answered:

Interesting question regarding cleaning asphalt shingles. Asphalt shingles are made with mineral granules imbedded in the shingles. The mineral granules provide protection for the asphalt matt. Anything that loosens the granules is to be completely avoided. An example is pressure washing. A common garden hose (without high pressure fitting) would be the extent of pressure washing. Losing the granules could be very detrimental to the life of the shingles. 

The real question is what solvent can be used to clean the mineral granules without damaging the asphalt shingle. You mentioned Sodium Hypochlorite. 12.5% Sodium Hypochlorite is used for shock treatment of a swimming pool that is in need of treatment for algae. No doubt that would kill the algae. 

What stains are you removing? Rust? Hard Water? I don’t know that Sodium Hypochlorite would remove those stains. The Sodium Hypochlorite at 12.5% would no doubt have a deleterious effect on the asphalt in the shingles. 

I have recommended household bleach and water (50/50) to spray on moss growing on roofs. This has been very successful in killing the moss. It is not necessary to remove the moss. It will dry and blow away. We have not noticed any deterioration of the asphalt shingle. However, 50% bleach and 50% water is not in the same league as 12.5% Sodium Hypochlorite. However, it is very successful in killing the growth. 

Several major shingle manufacturers have introduced algae inhibiting granules into their line of shingles. They claim very good results. The shingles look the same as regular shingles. This however does not enhance your roof cleaning business.  

To sum it up, identify the stain and use a remover that does not affect the properties in the asphalt shingle. Do Not administer harsh cleaning (pressure wash etc.) on the shingles. Avoid unnecessary traffic on the roof that is being cleaned.  

We thank you for your question. We hope this information will be of some value to you and your “startup” company. Seems like an interesting and possibly very profitable endeavor. Keep us posted on your progress. 

Your friends at AskARoofer. 

To start a business, I think you guys need to do a thorough study on it. Try to meet the professionals in person and ask for advice. Even though to the best of my knowledge to remove moss and algae, the asphalt Roofing Manufacturers Association (ARMA) advises a 50/50 mix of household strength sodium hypochlorite (pool chlorine) and water on the slate roof shingles.