Can't Neutralize Acid on Copper Awning


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Old 05-18-22, 06:12 PM
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Question Can't Stop Streaking on Copper Awning Prior to Poly Coat

Hello all...

I'm a homeowner of a 30 yr old home which has two beautiful copper awnings over the bay windows. We're repainting the whole structure and have determined we want these never-quite-patina'd blackish awnings to be restored to bright but not blinding cooper color.

Researched options and decided to go the vinegar/salt route with some extra elbow grease to avoid the challenges of working with Muriatic or oxalic acid.

Got the ladder, got up there, cleaned a panel down to the copper. Gorgeous. Until, I put any water on it. Moments after rinsing it with water, I see streaks of various dark shades of rust and bronze, some look like adonized copper (from a torching). So, okay, I think maybe I have some minerals in the water. So I went with distilled water. Same thing! I even ensured I was using a cleaned cloth. The best results seemed to be from a rag dipped in water (not sprayed with a hose).

All the instructional videos and blogs say just "rinse well with water, dry it, and a buff with clean cloth should restore the shine." Except these streaks do not come off with a wipe. Quick spray with vinegar/salt water and they are gone in seconds. But I don't think you're supposed to put on the (poly/resin/laquer/etc) protection with the acids un-neutralized.

I'm turning to this forum to hopefully try and understand what is causing this. I don't mind a little fading on the way to getting it coated, but it can't be streaky. Any ideas/suggestions on how I can get this coated without streaks?
 

Last edited by jmwolfe1008; 05-18-22 at 06:18 PM. Reason: Improve title
  #2  
Old 05-18-22, 07:25 PM
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My initial thought would be that you have some other metal present that is causing some instant dissimilar metal corrosion when wet. Could be a steel or galvanized drip edge under the copper or maybe steel or galvanized nails somewhere, or maybe a different metal counter flashing directly above the roof.

Instead of immediately rinsing with water you might try neutralizing the acid with a neutral cleaner and see if it makes a difference.

It could be minerals in the water or it could be the pH of the water. Odd that distilled water still did it. Since it did it primarily when doused with water I'm thinking dissimilar metal contact due to the splashing causing everything (all dissimilar metals) to be wet at the same time.
 
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Old 05-19-22, 06:12 AM
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I've always used a strong solvent (lacquer thinner, MEK...) to clean copper. It doesn't contain water to react with anything and it thoroughly degreases the surface.

If you were using a Scotch-Brite pad or similar make sure you use a new pad. If using a old pad that has been on other metals it will contaminate the surface.
 
 

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