Magnet tests are useful, agreed, but they're not always definitive. Just because a magnet doesn't stick doesn't necessarily confirm aluminum—could be stainless steel or even some alloys that won't respond strongly. Had a similar issue myself: magnet didn't stick, assumed aluminum at first, but after sanding off some paint and corrosion, turned out to be stainless. Sometimes you've gotta dig a bit deeper or even scratch the surface (literally) to be sure.
Good points all around, but sanding and scratching isn't always the best move—especially if you're dealing with an installed roof. Had a case once where the homeowner wasn't thrilled about me turning their roof into a scratch-off ticket... Sometimes a quick acid test or checking metal thickness can save headaches later.
Yeah, sanding an installed roof can definitely earn you some side-eye from homeowners... learned that lesson myself a while back. Acid tests are a solid suggestion, but personally, I try to avoid them unless necessary—some acids can discolor or compromise certain coatings if you're not careful.
I've found that checking the thickness or even using a magnet test for steel vs aluminum can often narrow things down quickly without causing any damage. Also, sometimes just looking closely at the seams or fasteners can give you hints about the type of metal or its coating. If all else fails, many samples can be identified by contacting the original installer or manufacturer directly—assuming they're still around and didn't vanish into thin air (been there too!).
Had a similar mystery roof situation last summer—homeowner had no clue what they'd installed years ago, and the original contractor was long gone. Magnet test helped narrow it down to aluminum pretty quick, but the coating was trickier. Ended up carefully removing a small hidden fastener and checking underneath for manufacturer stamps or markings. Got lucky that time... might be worth a shot if you're still stuck. Beats risking discoloration with acids or sanding someone's pride-and-joy roof.
"Ended up carefully removing a small hidden fastener and checking underneath for manufacturer stamps or markings. Got lucky that time... might be worth a shot if you're still stuck."
That's actually a pretty clever move—definitely beats playing chemist on someone's roof and risking permanent damage. I've seen way too many homeowners cringe when someone suggests sanding or acid-testing their precious metal roofs. You'd think we were talking about their vintage cars or something...
Anyway, another trick I've used in similar situations is checking attic spaces or crawl areas beneath the roof decking. Sometimes installers leave behind scraps, labels, or even old packaging tucked away in corners. Found an entire manufacturer's label once just sitting there collecting dust—saved me hours of guesswork.
Also, don't underestimate the power of local roofing supply shops. Those guys have seen it all and can usually ID obscure coatings or finishes just by eyeballing a decent sample. I once brought in a tiny piece of mystery flashing, and the guy behind the counter took one glance and rattled off the exact brand and color code like he was reading from a catalog. Felt like magic.
But yeah, if you do end up pulling a fastener, just make sure it's somewhere discreet—no homeowner wants to see you poking holes in their pride-and-joy roof (even if it's just temporary). Good luck with your detective work... roofs can be sneaky little puzzles sometimes.
