Roof Cleaning: Nothing But The Facts Please (Part Two)
In part one, we discussed what causes the black stains on asphalt roofs that is so often found on houses especially in the Southern United States. Now, we will discuss two of the techniques of removing the stains and why one way should be avoided.
There are generally two ways to remove Gloeocapsa Magma. Either with Sodium Hypochlorite or Sodium Hydroxide. This is where the debate begins. Some contractors use one and some use the other. So what is the difference and which is the best? Here are the facts.
Sodium Hydroxide is a chemical used in many different products and applications. Some of the better know are dish washing detergent, water treatment plants, oven cleaners and paint and stain strippers. It is also used as the main ingredient in roof cleaners sold at the big box stores.
Used as a roof cleaner it is applied usually with a pump up sprayer to the roof and allowed to set for a period of time. Then using some type of pressure washer someone will get on the roof and using pressure wash the chemical and stains off. As it is being washed off it looks like syrup or coffee running off the roof. Some of this is the algae, but some of it is also asphalt from the shingles.
As mentioned earlier, Sodium Hydroxide is used in oven cleaners and dish detergents. It is actually an excellent degreaser. It breaks down grease, oil, etc. to a substance that is water-soluble and easily disposed of. We use it to remove oil based stains from decks. In this case, used as a roof cleaner, it does remove the algae, but also kills grass, plants and can damage glass as well as break down the asphalt (oil based) in the shingle. It does not destroy the shingle because of the chemical’s strength and time left on the roof, but it does remove some degree of asphalt. And any amount of asphalt removed is too much. In my opinion, not the best method.
Sodium Hypochlorite is another widely used chemical in roof cleaning. Probably best know as the main ingredient in bleach, it works well at removing algae and mildew. As found in bleach it is around 5% by volume depending on the brand. Commercial Clorox brand is around 6%. Bought “off the shelf,” 5% bleach will clean a roof but it will take some time and probably several applications. The problem with store brands is the 5% is really not strong enough and Sodium Hypochlorite looses strength over time. It is hard to tell how long the bleach has been setting on the shelf and you can’t tell the strength until it is used. You may have noticed at the “dollar stores,” the bleach is weaker than at the grocery store. The reason is because the bleach has been pulled off the grocery store shelves because of it’s age and sold at a cheaper price at the dollar stores.
Most professional roof cleaning contractors will buy their Sodium Hypochlorite from a chemical supplier. It is fresh and also much stronger at 12.5% content by volume. Applied correctly, it is an excellent cleaner and does not harm the shingles. It is the only method endorsed by the American Shingle Manufactures Association.
Sodium Hypochlorite is caustic so precautions must be taken when being used. It will kill grass and plants if not properly applied and, it will also corrode metal and can etch glass if not used correctly. Safety precautions must also be adhered to. Chemical mask, gloves and protective clothing must be worn and run-off controlled. It is not for the homeowner, the do-it-yourselfer or an untrained contractor. It is however the best method of removing Gloeocapsa Magma.
So although there is a debate as to the best method to remove the black stains from roofs, like most anything else, there is a right way and a wrong way to do anything. Know the facts and you will know the right way. Roof cleaning can be done safely and effectively if done correctly. Those are the facts.
Douglas Johnson
Taskmasters Wood Maintenance
