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  for Metal Finishing since 1989
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White Rust When Does It Occur After Kynar Coating Is Applied

I am A Contractor and received a shipment of Kynar coated metal building panels. When we went to install them they had something under the coating. The metal building company is saying it is white rust and it is our problem because we had the panels on the job site for 60 to 90 days. All the articles I have read say talk about white rust forming in the galvanizing period non talk about after the panels are coated with a Kynar Paint? There was also no powder looking substance on the panels only something under the Kynar. When does white rust occur?

Sara Cullison
construction - Ocala, FL
2006

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January 8, 2008

When does white rust occur?

Aluminum oxidation or white rust can only occur after the coating is applied.

However, metal prep is everything in finishing. The metal is subjected to a 5 or 7 stage pretreatment process.

Stage 1 Acid or alkaline to strip aluminum oxide
Stage 2 DI or RO rinse to remove product from stage 1
Stage 3 Mild acid or alkaline to further clean part
Stage 4 DI or RO rinse to remove product from stage 3
Stage 5 Chrome or non - chrome conversion coating
(final sealer)

If an aluminum or galvanized part is pretreated properly then coated with Kynar 500 liquid or powder coating. White rust could only occur if the coating was not applied properly. Kynar 500 coatings seal the part and does not allow oxygen to permeate through to bare metal.
Best regards, Kerry Nelson Organic coating chemist

Kerry Nelson
- Clearwater, Florida