Recommendations for painting over Zinc

[Pounder]

Hello, any paint/chemist experts with experience top coating over zinc chromate? My local expert recommends an epoxy barrier. I don’t doubt this guy but wanted to survey the braintrust.

 

[David Paule]

If you overcoat the zinc chromate, the new paint will be limited to the adherence of the zinc chromate to the base metal. Epoxy sticks way better than the zinc chromate I'm familar with these days. But if you have a good older professionally-applied zinc chromate, that's probably close to as good a bond to the aluminum.

How well the new coating will stick to the zinc chromate, I can't address.

Dave

 

[AzAero]

Try wiping the zinc chromate with a solvent such as MEK or acetone. If it immediately attacks and softens you most likely will have compatibility issues with urethane topcoats and even epoxy primers, best to just completely remove and start over. If it passes the solvent test and appears to be a sound coating you could thoroughly clean, scuff, epoxy prime and top coat.

 

[Roadjunkie1]

Try wiping the zinc chromate with a solvent such as MEK or acetone. If it immediately attacks and softens you most likely will have compatibility issues with urethane topcoats and even epoxy primers, best to just completely remove and start over. If it passes the solvent test and appears to be a sound coating you could thoroughly clean, scuff, epoxy prime and top coat.

Did you paint the zinc chromate on? If this is an older airplane, VeriPrime was a DuPont product that was a two-part epoxy and will STICK. My airplane was pained with VeriPrime in anticipation of me painting it someday. That was in 1997. She has flown since then, including sitting in the Sun for events like, say, OSH, and has shown no signs of the primer parting company with the airplane. If it is a two part, you might just need surface prep as above. Otherwise you might need to....erk....erk......erk......remove it.....IMHO...