Just to let you know what happened to me last week. The day was going bad & I mixed up a batch of LUV but I for got to take my hose out of my 12.5 SH barrel therefore most of the roof got straight 12.5 bleach. I didnt realize it until later that evening. The next day it rained but I was`nt able to get to finish it until today. I was thinking that the shingles would be curled up. But much to my surprise where I sprayed it was Algae Free. So if you accidently spray straight SH the only thing is that it`s very costly spraying.
Being asphalt based, even 12.5% SH will not hurt shingles. SH does not attack the asphalt the same way hydroxide will. But yea I agree,...extra money spent that time. Just charge the next few customers a little more to recover your loss,...ha,ha just kidding,...I think!!