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Exterior door with bronze aluminum threshold over copper sill pan – galvanic corrosion?

ia42 | Posted in General Questions on

We have a front entry door with water damage issues like those mentioned in the GBA article,  ‘Sill pans for exterior doors’.  The article mentioned that copper sill pans are good, but I’m wondering about galvanic corrosion.  One quote we got was for a Thermatru fiberglass door with a bronze aluminum threshold over a copper sill pan.  Prior to receiving the quote, I happened to read about copper and aluminum being two metals that when used together would result in galvanic corrosion.

Any thoughts? (Thanks!)

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  1. Expert Member
    Michael Maines | | #1

    Ia42, this is one of many charts available online that show the potential for galvanic reaction between dissimilar metals. It shows that yes, galvanic reaction is likely to occur if aluminum and copper are in contact with each other. You could just add a separation layer of Vycor (a butyl membrane) or similar between the metals; if they aren't in direct contact and not sitting in water the reaction won't occur, or will be slowed to the point that it won't matter.

  2. tommay | | #2

    If you add an insulator as Michael suggest maybe you can add some wiring and charge some batteries at the same time :)

  3. Expert Member
    Akos | | #3

    If I remember correctly with copper and aluminum it is the aluminum that will corrode over time. The threshold has a lot of material there, I think it will take a very long time with a lot of standing water to have issues. The earlier suggestion of peel and stick between the two would eliminate any worries.

  4. Expert Member
    Peter Engle | | #4

    Or you could use one of the plastic sill pans available on the market. Or, just form the sill pan with Vycor and skip the copper. I've seen the inside dam of a copper sill pan sweat in the winter because it's pulling so much cold from outside.

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