Masonry stain removal
#2
First thing I would try is a bottle of Limeaway and a light scrubbing with a toothbrush or similar. (Not scrubbing so hard you take the shingle grit off.)
it will take many repeated applications and you should let it soak. Lay a washcloth on it and soak the washcloth in Limeaway for several minutes then scrub, then do it again.
A dilution of muriatic acid would also likely work but i would worry it might discolor the shingles.
At any rate, rinse it well when you are finished. Check the chimney cap since it looks to me like water is probably getting in behind the stone... leaking out the bottom.
it will take many repeated applications and you should let it soak. Lay a washcloth on it and soak the washcloth in Limeaway for several minutes then scrub, then do it again.
A dilution of muriatic acid would also likely work but i would worry it might discolor the shingles.
At any rate, rinse it well when you are finished. Check the chimney cap since it looks to me like water is probably getting in behind the stone... leaking out the bottom.