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2/1/2016

Powder Coating Q&A: Can Powder be Applied Over Zinc Plating?

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Can powder coating be applied over steel parts that have been zinc plated type II SC2 black?

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Q. Can powder coating be applied over steel parts that have been zinc plated type II SC2 black?

A. Plated surfaces are always a challenge for adhesion of an organic coating such as powder. There are certain types of plating that powder will not bond with very well. Type II zinc plating indicates a colored chromate conversion coating.

In general, the answer is yes, you can powder coat it. However, caution is advised. A chromate conversion coating can be a very good corrosion inhibitor, but may not be very good for powder adhesion. The chemistry is not conducive to good adhesion.

I would do a sample to check if the powder wants to stick to the zinc plated surface. If the adhesion is not good, you may need to roughen the part with a very light blast, tumbling operation or something similar to create some surface roughness. The roughness may help you overcome the lack of chemical compatibility and provide a good surface for mechanical adhesion.

 

Originally published in the February 2016 issue.

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