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Zinc electroplating vs galvanizing

I work for a company that is starting to build ornamental fences. We are a little confused about what type of "anti-rust" we should use. There are some companies in my area that offers different type of finishing. The problem we are facing is that these fence are powder-coated (polyester)and I've been told that powder coating over galvanized steel could cause problems (the paint doesn't stick very well and the surface is not very smooth) but I've been told that's not the case with Zinc Electroplating. What about the rust protection? is Electroplating better? cause as far as I know, Galvanised goes everywhere (inside the fence tubing) and that's not the case with Zinc electroplating.

Thanks in advance,

Patrick Marseille
- Blainville, Québec, Canada
2004

Painting over galvanizing is not a problem if you can find a person who has experience. Surface preparation is key (see many past paint over galvanize questions in this forum). Painting over galvanizing is very common and you have a few people in your area that can do it.

Mike Stroia
Galvanizing - Canton, Ohio
2004

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Patrick,

It is possible to Plate in Alkaline Cyanide Free zinc to a thickness of say 30 microns , chromate in yellow phromate then Powder coat. Entirely possible. It is being done. Galvanising too can be powder coated, using a good chromate correctly applied first.

Good Luck,

Asif Nurie [deceased]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016
2004

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Good questions. You want your fences to remain properly ornamental. I don't have much experience with the painting issues, but as far as galvanizing, a hot-dip galvanizing coating may be as thin as a couple of mils and as thick as 15 to 30. Electroplate will generally be well under 2 mils. (Just to make it complicated, the suppliers in both American and SI units specify the hot-dip coatings in ounces/square foot rather than thickness - if I recall, one oz/sq-ft = 1.7 mils.)

The corrosion protection, long term, will be determined by the thickness of the zinc. A well-done paint coating applied over the zinc will further extend the life. Where there are holidays, damage, or weathering of the paint, the zinc will protect the steel and it will not rust until the zinc is mostly through.

From the very long term view, to maximize life particularly in industrial or seashore environment, heavy hot-dip galvanizing is needed. Once you coat any such structure you get better life but if it's visible / ornamental you may be committing yourself to coating maintenance, or face a poorer appearance.

Paul Tibbals, P.E.
gas & electric
San Ramon, California, USA
(My opinions are not related to nor a statement of my employer's)
2004