This is our most recent project. This roof had alot of black algae as well as ample lichen. Lichen is real roof killer since it has such strong grip on the roofing granules. There is always the possibility of scars left where the lichen once was. Black stains are removed instantly. Lichen will come off after a few rains after it is treated. This roof was not pressure washed, power washed, scrubbed or scraped. We never stepped a single on this roof to clean it. There was far more sq. ft. then what was shown. The cost of cleaning this roof was 1/15 the cost of roof replacement.