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Hey Ray happy to field this one for you. Lets take this roof slow since it will be your first asphalt, when you approach this roof you will take your usual precautions watering,run off and such. Start at one end and apply your mixture { dont worry on this one about hitting the tuff stuff first, that will come in time } coat the entire roof and wait at least ten minutes before a re application, if its around fifty degrees or less you can wait twenty to thirty minutes giving it a chance to work. Now after your first application any Moss or Lichen will turn white...thats it it's dead no need to rehit...if it's a lil heavy you want to give it a quick squirt go ahead but again once it turns white it cant get any deader.{not a real word } These applications are done on the same day...{ usually two is all you will need }you do not return to this roof to treat it again, you wondered also about returning after it's dead and dried up, no need its dead and dryed up. " Spray,rinse and repeat" I probably rinsed down about one hundred asphalt roofs....a waste of time, letting it sit on there does a much better job! Also I never rinsed and then re applied, it would be useless. Spray it on and leave it all for the rain, I promise you it will be fine. If you need to lean on me when you are doing the job feel free to call me....it's cold up here so I aint doing anythig. Good Luck!

As a  newbie, the second roof I'll be doing this spring is a 88 year old asbestos roof. A neighbor and it's a freebie. I guess newbies and freebies go together.

Not much moss or lichen but totally discolored do to 88 years of air pollution up here in the frozen north. This seems to be the case with most of the asbestos roofs I've seen in the area and there are a lot of them.

Someone has suggested that I use a "soft" pool brush between applications and that it might take three applications. Am planning to use 50% SH on the first two applications and 20% on the final one.  I understand that I should NOT be using ISP in the mix. ???

My major concern in the patenea colored flashing in the valleys.  Am I going to cause them to discolor or what?

Because I'm using heavy SH and and three application, after this free one, with lots of pictures taken, I'll charge about 60 cents per sq of roof area

Jim - On an asbestos shingle, I would not suggest using any brushing or agitation that could dislodge any portion of the shingle. Typically these roofs are categorized as Non-Friable so they don't cause any health issues BUT if you start brushing and small particles become dislodged you might run into a problem, especially if a nosey neighbor contcancerts the authorities. Going so hot with a 50/50 mix seem like overkill to me also, I'd probably stick with multi applications of a 30% mix. Don't know about the patina, but if it's copper, then it should look good whatever color it ends up.