"Makes me wonder, is there an easy way to test if two metals will react badly before installing them together?"
Good question—galvanic corrosion can sneak up on you. A quick way to check compatibility is by looking up a galvanic compatibility chart online. Basically, metals further apart on the chart tend to react more aggressively when they're touching, especially if moisture's involved. Copper and aluminum are pretty far apart, which explains your brother-in-law's gutter discoloration issue.
If you're looking for a hands-on test, you could try a small-scale experiment: clamp or tape small samples of the two metals together, dampen them slightly, and leave them outside for a week or two. If there's noticeable corrosion or discoloration, that's your red flag.
Speaking of copper roofs... did he end up swapping out those gutters, or did he find another workaround? Curious how he handled it in the end.
"If you're looking for a hands-on test, you could try a small-scale experiment: clamp or tape small samples of the two metals together, dampen them slightly, and leave them outside for a week or two."
That's actually a pretty clever suggestion—I wish I'd thought of it before installing aluminum flashing near copper a few years back. Let's just say I learned about galvanic corrosion the hard way... and my wallet still hasn't forgiven me. At least your brother-in-law caught it early!
Yeah, galvanic corrosion can sneak up on you pretty quick... learned that lesson myself a while back. I had a similar issue when I replaced some flashing around a chimney—thought I'd save a few bucks by mixing metals. Big mistake. Ended up having to redo the whole thing within a year.
One thing I've found helpful since then is checking out galvanic compatibility charts online before pairing metals. They're pretty easy to find, and they give you a good idea of which combinations are safe and which ones will cause trouble down the road. Also, if you're stuck with two incompatible metals, you can sometimes use isolation materials like rubber or plastic washers to keep them from touching directly.
Anyway, your small-scale experiment idea sounds solid—wish I'd thought of that before diving into my own DIY disaster. Curious to hear how it turns out if you decide to give it a shot...
Good call on the galvanic charts—saved me a headache more than once. Curious though, have you considered how weather exposure might speed up corrosion in your experiment? Might be worth factoring in rain or humidity somehow...
"Curious though, have you considered how weather exposure might speed up corrosion in your experiment?"
Good point—humidity and rain definitely accelerate corrosion. If you're testing outdoors, try angling the sample slightly to mimic real roof runoff. I've seen surprising differences just from adjusting the slope a bit...
