Q: Help me understand Rinse Pressure
Peter G from Pace, FL
A: Low Pressure, but not NO PRESSURE
Run the Rapids
One way to look at the situation is to zoom in on the asphalt shingle texture. Essentially you can think of the aggregate or granules as being rocks in a river bed. Then add to the river bed dead leaves (which will be the algae and mold that the roof cleaner killed).
When you rinse with a garden hose you are providing so little water that the ‘leaves’ are riding class 4 rapids bumping over every boulder and essentially getting stuck in the valleys.
Thinking of rinsing this way you can get a sense of why the distant garden hose rinse just doesn’t get it.
River Flood Level
The way to avoid your black streaks running the rapids is to rinse with plenty of water, enough to rise above the granules, so that the algae and mold have a smooth surface to ride the water down to the gutters.
Think of footage of floods where cars and other debris float freely as the waters rage.
Low Pressure, High Volume Rinse
So the ultimate combination we need to make it all work is enough pressure at the base of the algae to lift it into the high volume flood of water racing down to the gutters.
This combination of approx 200psi of lift pressure, combined with the high volume out put let’s the mold and algae float unobstructed down the roof into the gutters…
When the flood waters recede you have a much cleaner roof.