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Dip painting galvanized tubes



Duplex Systems: Painting Over Hot-Dip Galvanized Steel
DuplexSystemsThumb
(free download from AGA)




affil. link
Latex Self-Etching Primer

2002

I am dip painting 3" OD 18 gauge round tubes 7' long with a flat black paint. The tubes are galvanized. The paint finish looks great, however, it can be scraped off with your fingernail. How can I safely etch the galvanize coating before dipping to ensure paint adhesion? I was previously told to try cleaning the tubes with vinegar. It did help, but very little.

Thank you,

Thomas H. Mentecki
- Springdale, Pennsylvania


2002

Hi, Thomas. The American Galvanizers Association at www.galvanizeit.com has a booklet on "Duplex Finishing" by which they mean galvanizing followed by painting. But in brief, galvanized surfaces which are intended to be the final finish have a chromate treatment which paint does not adhere to. When painting is intended, the chromate treatment is omitted.

I would clean the pipes in a hot slightly alkaline cleaner rather than with vinegar. I've also been told that scrubbing with a solution of trisodium phosphate [affil. link to info/product on Amazon] will remove the chromate. Then apply a self-etching primer before the dip paint. Good luck.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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