Still fairly new to soft washing, have done multiple brick houses and other exteriors walls, all have turned out excellent. Starting to practice on friends roofs to really tone my craft. I am just not getting the results I want, attached is a photo of a roof I did today, I used a 4% pure CH mix with surfactant. You can clearly still see brown patches. Does anyone have advice on 1) what these patches are and 2) how to properly remove? This is the 2nd roof I have done with same result.
Thank you for the help in advance.