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Ted Mooney, P.E. RET
Pine Beach, NJ

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Zinc Plate vs E-Coat

Q. Which finish has a lower coefficient of friction when applied to steel: e-coat or zinc plate? I have heard that zinc plate has "lubricating" properties and is slicker, but e-coat is a more smooth surface.

It seems like powder coat adheres a lot better to e-coat in comparison to zinc plate. We do a lot of e-coat with powder overtop for added corrosion resistance. Should powder over zinc not even be considered?

Is there a good resource (book, manual, etc) anyone can recommend to learn more about finishes?

Robert Schulte
- Wentzville Missouri
October 22, 2024

A. Hi Robert,

I would agree with you that powder coating usually adheres a lot better to e-coating than to zinc plating, but it's not because of the zinc plating per se but because zinc plating almost always receives a chromate conversion coating, which is not an ideal undercoating for paint. Zinc plating can by zinc phosphated in lieu of chromating, and if this is done I think you'f find the paint adhesion excellent.

Still, the corrosion resistance of zinc phosphating, followed by e-coating, followed by powder coating is excellent in my experience. I doubt that the corrosion resistance of zinc plating, followed by zinc phosphating, followed by powder coating would be better.

Usually available on eBay;

sometimes on
AbeBooks or Amazon

(affil links) mfg_online

free pdf is currently available from academia.edu

Zinc plating is probably better as a stand-alone corrosion resistant finish than as an undercoating for powder coating. In stand-alone applications it is a hard metallic finish rather than a soft organic finish. In those applications it is bright, reasonably wear-resistant, very strongly adherent, and thin enough to be useful on machine parts and tight-fitting nuts and bolts. Unfortunately, I don't know the coefficients of friction for zinc plating and the various powder coatings, but I imagine they're highly variable anyway. I do not agree that powder coating is smoother; rather, it's a softer finish which may feel smoother. But if there's any significant wearing force, metallic finishes like zinc plating are usually more durable.

There are lots of good finishing books, but the Metal Finishing Guidebook ⇨
has the advantage of, for now at least, being free :-)

Luck & Regards,

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

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