Tuesday, June 11, 2013

Askthe Engineer about copper and aluminum reactivity

Question: I have copper gutters on my home. They were installed by the previous homeowner. I'd like to get gutter covers installed but don't want the extra expense of copper. Being two dissimilar metals, how do you insulate the aluminum gutter guards from my copper gutters.

Answer: In spite of the very low chemical reactivity of copper and aluminum we did initially (21 years ago) insulate the aluminum gutter guards (then it was unpainted) from copper.

A couple years later when we inspected these jobs we found that the insulation we chose had deteriorated. Nevertheless, just as the reactivity tables suggest, there was no visible signs of interaction between the copper and aluminum. There was however major reactivity between the plated steel screws and copper.

We switched to a 410 grade magnetic stainless screw and stopped insulating between the copper and aluminum. Now, nearly twenty years later, we have not observed any reactivity between the aluminum (we now use painted aluminum) and copper. The stainless screws are also nonreactive.

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