Asphalt Shingles need to be cleaned every 3-5 years to remove the growth of black algae "Gloeocapsa magma" that will develop into ugly black streaks. If left untreated, green moss and lichen will also develop and with their roots can cause permanent damage and take longer to remove.
This photo is a recent roof clean we did that was on tank water so the run off needed to be diverted away from the tanks and left disconnected for 4-6 weeks. June is a perfect time of year to clean Asphalt Shingles as the available rain quickly dilutes and washes the excess chemical away so that the customer can quickly reconnect their tanks.
We have performed this service for customers on tanks many times and have never had any customers complain about drinking water contamination.
Method:
We use the manufacturer recommended method described by all major manufactures, this process is a soft wash using Sodium Hyper-chlorite that kills the algae quickly and then is washed away after with water. This provides instant results without damaging the shingles and warrantees.
We follow Americas leading Shingle Supplier "Pabco" cleaning method.
Outlined here -> Recommended Maintenance Practices
It is highlighted in this manual that only bleach and water must be used to clean asphalt shingle roofs making most commercial cleaning such as 'wet and forget rapid' and '30 Seconds' products not suitable due to their use of surfactants that do not wash off properly and can cause damage to the asphalt shingles.
Benzalkonium Chloride should never be used on asphalt shingles as it does not wash off easily, has been known to cause damage to shingles and can cause leaks when the water thickens with the surfactant. This makes most moss and algae treatments like "Wet and Forget" that mostly rely on Benzalkonium Chloride in their products.
Results are typically achieved within 1 day and last around 3-5 years before needing to be cleaned again. There is no way to prevent regrowth like with the use of Benzalkonium Chloride.
If you have an asphalt shingle roof on tank water or in the city centre, give us a call and we can help you bring your roof back to new. Contact Us