Metal Roofs helped by sacrificial electrodes?

[Stephen Tashiro]

Would "sacrificial electrodes" (like the kind used to protect evaporative coolers from rust here in the SouthWest) help metal roofs resist corrosion? I assume the way you would use such an electrode is to connect one end to the roof and the other to a metal pipe driven into the earth.

[Joe Pelonio]

I thought the sacrificial electrodes were for prevention of corrosion caused by the electrochemical reaction between two dissimilar metals in contact with water. If that's true an aluminum roof installed with aluminum roofing nails shouldn't need it.

[Mitchell Andrus]

You might look for an 'active' system, similar to those used by people who put antique cars away for long periods. Many auto museums use such a system. I don't know how fussy these set-ups are though.... Isolating the parts from the ground and rest of the structure (rubber grommets) may bust the budget. I'd call a company that sells metal pre-fab buildings.

[Stephen Tashiro]

The metal roof panels in the local hardware stores are too stiff to be pure aluminum. The handyman books says that corrosion is what causes metal roofs to fail, so I was assuming the roof panels were steel.

[Rich Stewart]

Isn't a sacrificial electrode just a softer metel that will corrode first instead of what you are trying to protect? Like a outboard motor.

[Mike Hood]

Yep. The sacrificial metal (anode) just has to be further down the galvanic series than what it's trying to protect. For steel for instance, zinc is a very good sacrificial anode. HOWEVER... unless you're getting true galvanic corrosion (caused by the reaction of two dissimilar metals) then all the anodes in the world won't help you.

Plain old rust (oxidation) can't be stopped unless you remove the oxygen and/or electrolyte. Paint is your best friend.

[Spencer Hochstetler]

Yep. The sacrificial metal (anode) just has to be further down the galvanic series than what it's trying to protect. For steel for instance, zinc is a very good sacrificial anode. HOWEVER... unless you're getting true galvanic corrosion (caused by the reaction of two dissimilar metals) then all the anodes in the world won't help you.

Plain old rust (oxidation) can't be stopped unless you remove the oxygen and/or electrolyte. Paint is your best friend.

Yes. Though a more general statement would be to "remove the oxidant, of which oxygen is a common one." I have seen va$t quantitie$ of corrosion occur non-galvanically in the absence of oxygen.

[Mike Hood]

Very true. Any oxidant would work. Heck.. with today's acidic rain... no telling what you might get in rainwater these days. :)