"certain detergents can leave a filmy residue if you don't rinse thoroughly enough"
Yeah, learned that one the hard way... spent an afternoon scrubbing off streaks after using some cheapo store brand stuff. I've had decent luck with Dawn—seems to rinse cleaner. Anyone else swear by something different?
Dawn is pretty reliable, but honestly I've had better luck with Simple Green. It's gentle enough not to damage finishes, yet strong enough to lift grime or that weird residue you mentioned.
"spent an afternoon scrubbing off streaks after using some cheapo store brand stuff."
Been there... wasted half a Saturday cleaning streaky siding after a storm cleanup. Switched to Simple Green afterward and never looked back. Might cost a little more upfront, but saves a ton of hassle down the line.
Simple Green's decent stuff, but have you tried it on metal roofing specifically? I mean, siding and roofing finishes aren't always the same animal. I've seen some cleaners that work wonders on vinyl or painted surfaces but leave weird discoloration or dull spots on metal panels.
Not knocking Simple Green—it's saved my butt a few times—but I'd test it out first on a hidden spot if you haven't already. Also, what kind of metal are we talking about here? Aluminum, steel, copper...? Makes a difference in how it reacts to cleaners. Had a homeowner once who got a little too enthusiastic with a popular cleaner (won't name names, lol) and ended up with a roof looking like a tie-dye shirt.
If it's just some random sample you found lying around, might be worth experimenting on it first. Better to mess up the mystery piece than your actual roof, right?
Good call on testing first—I learned that lesson the hard way myself. When I moved into my place, I assumed a cleaner safe for aluminum siding would be fine on my steel roof panels... ended up with some dull patches that took forever to buff out. Definitely smart to experiment on your mystery sample first. And yeah, Simple Green's usually reliable, but metal finishes can be finicky. Hope your test goes smoothly and saves you from any headaches down the line.
"metal finishes can be finicky"
Definitely agree with this. When I had to clean my metal roof, I found diluted dish soap and warm water was gentle enough to avoid dull spots. Might be worth trying on your mystery sample first... good luck!
