If the first treatment doesn't remove all the bleak algae in 10-15 min, do i wait til the roof dries then re-apply or just re-coat it as soon as i'm finish with the first treatment? Their has to be a rule of thumb.
How long to wait? That depends on the temperature, the colder it is the longer you have to let it sit so it can work. No matter really what the temp. I give about 10-15 minutes between coats.
As a rule of thumb, we usually attack the dirtiest portion of the roof first. That way it has more dwell time and we can usually tell if a second application is necessitated before we roll up our equipment.