Really dirty old slate roof- need some advice please

i could use some advice on this one. it’s about a 100-year-old house with slate roof. customer is pretty serious about having the tiles cleaned. i’ve never done slate this bad or on this scale before. This house is about 5000 square feet.

i’m thinking a 40’ lift would make sense, and just treat it with SH and water (no soap), then maybe a moderate rinse at 500 psi or so to clear the dead algae and moss. how’s that sound?

also, any estimates oh how a long a job like this would take you? I can figure my pricing/costs, just not sure on how to figure time.

I would plan on two applications several weeks part and then maybe one touch up. My, what a beautiful home that is. I would budget two lift rentals and twenty five man hours.

[MENTION=6510]Tim4[/MENTION] thanks sir! that’s good info. so no rinse then?

i’m not sure the weather up here is going to allow me to space the job out over a couple of weeks though. might have to wait till spring.

I was ground man on a shingle roof job today. 55 degrees and the reaction was slow. I’ve tested a few slate roofs but not done a ton. I really can’t imagine that hose rinsing would have much affect on decades worth of growth. Several rains usually help though.

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