Hi guys. I talked to Chris T. earlier today about this and he had some great suggestions. I'm curious what the rest of you would say....? This is a cust. that I've done 2 previous asphalt shingle jobs for. He'd like me to clean these non-painted, galvanized metal roofs in the pics. Until talking with Chris, I was totally in the dark as to what mix to use and what to rinse with. There are a few trees overhead, so I'm sure there are some tree droppings mixed in, along with the usual crud that collects on these. One of my main concerns is causing any rust.
All I can say is contact the aussies ("idontknow" screen name for one, SEARCH AUSSIES) as they have a LOT of metal roofs down under and have posted in the past regarding metal roof cleaning. hope that helps.
I would go with a mix of 35% SH, H2O, Surfactant and scrub any stubborn spots with a deck brush. Rinse completely with water and you should be fine. Anything galvanized will rust over time but this roof will not be exposed to SH on a continuous basis and you will be rinsing it thoroughly when finished.
Thanks Ray and Maverick! Looks like I'l get to use the 16' ext. pole and brush...... Don't wanna end up on the ground the hard way! Thanks for the link, Ray.