Zinc electroplating onto a galvanized surface

A. Hi Hemant. My experience is in the electroplating field, where I never once saw zinc electroplating reworked with an extra layer on top of the original; rather, it was stripped before replating every time.

But regarding zinc plating onto a hot dip galvanized surface, where the zinc coating is much thicker, although I've personally not previously heard of it, it's an interesting question. Please flesh it out with more information about your situation and why you might want to do this because certainly the devil is in the details: old work vs. new work ... chrome passivated vs. bare ... uniformly galvanized surface vs. sheared parts where surface is partially zinc and partially steel ... could zinc whiskers pose a problem in the application ... If it's in an effort to salvage defective parts, I think the odds of success go down.

Almost surely the blistering is because of inadequate prep. The parts are not clean and waterbreak-free, or have not been adequately acid activated, or a chromate film is interfering with adhesion. Thanks!

Regards,