We did a roof last week. Used the apple cider sauce mix. The roof was badly streaked, and lots of lichen growing on it. Most of the roof came clean with one coat.
The spots that had dark streaks, we put down two coats. I checked back on the roof the other day, have had rain almost everyday since the roof job, the lichen and all but one spot on the roof look great. Question is, if the mix was good enough to get rid of the lichen, shuldn't it have been good enough to get rid of all the dark streaks ?
Or is there some other reason for the dark color ? I did notice in on area on the roof that there was indeed tar seeping out from the shingles. I do not know if the homeowner had a leak, and they repaired it by replacing the shingles with extra tar under them. This is the same spot where there seems to be dark shingles.
If a comp roof suffers enough granule loss, I've seen the tar appear as streaks and dark patches before. Even with strong mix, the lichen doesn't die and fall off right away. I'd double check your mix measurements. Maybe there was not enough alcohol to help penetrate? It is baffling, but a pic would help.