Mark,
Currently, I use Gutter Zap to wash aluminum homes. Just have to be certain to get it all off of the windows. Gutter Zap does wonders on gutters (dilute 2 to 1)
I also use it on the alum siding, but dilute it 10 to 1 or so.
I am always looking for a better way.....I'm curious to see what everyone else uses.
If there is mildew present, I use a different cleaner, with some bleach mixed in.
Also, I never use more then 2000psi on alum. siding.
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Mike Hughes
Everclear
Souderton, PA