I take aluminum regularly. There’s been a few that concerned me and I talked it over with the customer prior. Showed them the chalky finger swipe and a little explanation and warning. I suppose I could still be burned without it in writing. Hopefully I’ll see some red flags prior to.
Went to a house last year, 3 sides were vinyl and 1 side was alum…looked nearly identical. The owner was there as I was getting ready…made the statement that last time it was washed, the guy had to repaint the alum section. Upon that disclosure, I realized the wall was indeed alum…promptly passed on the job. I have washed a bit of it and never had problems. Matter of fact, I washed an office building on Mar 26th that had alum gables…told the owner my concerns, she said wash it and if it turns that she would repaint because it had to look better. I washed it and it turned out great.