I know what you mean. I just recoated my roof with 2 coats of Rustoleum acrylic coating. After drying. stuff from my cedar trees fell on it and stained the new coating. After a month or so I got tired of looking at the stains so I got up on the roof and put car wash and warm water in a bucket and brushed the roof, let it set for 20 mins and then hosed it off. I usually put bleach in the water along with Ajax but because the coating was new I just used soap and water. I had to use a 1700 psi power washer to remove most of the stains and dirt, the hose did not do a good job. I wish I had another place to park it away from the trees.