One of my regular clients has a roof with synthetic slate shingles, their basically plastic shingles (blue in color). Over the years, and with all the shade tree's, a black film has gathered on them. Last year I didn't know anything about roof cleaning pumps, but plan to invest in one soon, I tried to clean this roof with a higher concentration of house wash and my x-jet with no luck. The only thing that would clean the black film was F-13 and a gutter brush. The client REALLY wants me to walk it and use high pressure (not a fan of this method), but it's at least a 8/12 or 10/12 pitch and slick as snott when wet!
My question is will the roof wash recipes I've found on here really work on this type of roof, and has anyone successfully clean one of these roofs before. It's a ranch style, so I'm sure it could be done from the ground. My biggest concern is how fast the chem rolled of the roof the last time I tried, so would something good and foamy be better?
