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diy'er on LI 08-15-2009 07:56 PM

copper "roof" to bay windows stained siding..
so our new siding and windows are almost done.... yay! The only thing they did NOT replace is a piece of (probably aluminum) siding just above the windows that forms the base of the cooper "roof" for the bay windows. The copper is 35 years old, and has a lovely green patina.

Problem is that the oxidized copper has created a greyish water stain on the piece of aluminum (or maybe vinyl?) siding immediately beneath it.

Once they're done with the installation, and the scaffolding is gone, I want to tidy-up that little piece of siding. But with WHAT?

I was thinking something like CLR (the bathroom cleaner), but I'm also concerned that since cleaners that remove rust stains and oxidation marks are super-potent, they may ruin the paint on aluminum siding, or the vinyl, if it's vinyl siding....

any one have any experience with a cleaner that works? was it on aluminum or vinyl or both?


diy'er on LI 08-15-2009 08:11 PM

just read an abstract on an electrical engineering article that says that copper oxide can be etched off of a surface with acetic acid.

anyone ever use vinegar? did it work? Not comfy with the idea of smearing lab grade (concentrated) acetic acid right above the new windows...


Gary in WA 08-15-2009 10:48 PM

I clean my copper pennies with vinegar........
Be safe, G

Tom Struble 08-16-2009 11:16 AM

the grayish stain may just be the finish on he aluminum has chalked off and what your actually are seeing is the bare metal thru the paint

i would clean the aluminum and prime and paint it with a high quality paint

diy'er on LI 08-16-2009 03:25 PM


Originally Posted by tomstruble (Post 315133)
the grayish stain may just be the finish on he aluminum has chalked off and what your actually are seeing is the bare metal thru the paint

i would clean the aluminum and prime and paint it with a high quality paint

yeah, that could be it too. I'll first try the vinegar (since it really looks like water runoff stains)... if it doesn't work, I'll prime and paint.. thanks!

Marcia Hamilton 04-24-2012 03:37 PM

Just installed a large bay window with a beautiful copper roof. Our house has light gray aluminum siding.
NOW I learn from a friend that you should NEVER put a copper roof anywhere near aluminum siding.
Didn't understand why until I read above comment. Apparently the copper can stain the aluminum.

OMG - what should I do now?

Marcia Hamilton 04-24-2012 03:41 PM

Re copper roof creating stain on aluminum siding where it meets the roof...aluminum siding is light gray,
in perfect condition (painted fresh 2 years ago) and need advice on what to do to prevent staining by
copper. I do NOT want to keep re-painting the siding.

Contractor NEVER mentioned this problem to us. I feel it is fari and reasonable to make him pay for whatever
remediation is necessary.

joecaption 04-24-2012 03:59 PM

Your not even sure if it's aluminum or vinyl. May want to figure that out first.
Old alumium and vinly siding caulked, it just wipes right off, try that first.
If you wipe you hand across the siding and there coloring on you hand it's just caulking.

Marcia Hamilton 04-24-2012 04:07 PM

Copper roof on bay window and aluminum siding
It is definitely aluminum siding. Just found an article through
Google "Preventing Electrolysis" which says that two metals should
not be placed in contact or near contact, with each other.

It says a contractor should know about the problem of a metal's (or an
alloy) reaction to other metals. It said that when two different metals are in
contact with each other in the presence of moisture, there will be a flow
of current from one metal to the other metal, and one will be eaten
away !!!.

Sound like I'm out of luck - or should I say my contractor is out of luck.

user1007 04-24-2012 07:07 PM

Any time you put different metals next to each other and add moisture you risk an electrolytic reaction. It is why water heater valves used to fail with copper, brass, steel etc. hooked together.

I remember mounting a sign for an artist and needed to go into brick. The sign was a copper printing plate, the screws brass, and the masonry anchors zinc. I did it with plastic sleeves and silicon so hopefully no two metals will ever touch.

Your contractor should have known to expect a reaction. It is not just staining to worry about. Eventually either the copper or aluminum will errode and fail.

I have installed copper countertops for some clients and they look nice for awhile. Believe it or not, ketchup---mildly acetic---works as well as anything at restoring the brightness.

You have a different situation though. Can you insert a plastic or nylon barrier between the aluminum and copper without it looking tacky? That should prevent the metal to metal contact.

You do know the oxidation from the roof is going to drip on any siding though right? Do you need to enhance your gutter situation? Do not create the same situation with incompatible metals between roof and gutters though!

Marcia Hamilton 04-24-2012 08:48 PM

Copper roof on bay window and aluminum siding
THanks for the post about metals together. I don't have a gutter
problem BUT dripping onto the aluminum siding below and around the
copper roof vs. just the area at the top of the roof where it joins
the aluminum siding is another problem.

THe only solution I have come up with so far is replacing the aluminum
siding above, around and below the roof with clapboard. Unfortunately,
this big bay window is one story above the ground...

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