Metal finishing Q&As since 1989

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How to tell Hot Dip Galv vs. Electroplate

I work for a contractor who is installing steel platforms and handrails which we had fabricated and galvanized by a subcontractor. The construction manager on the job claims that the materials are Electroplated not Hot-Dip Galvanized as they were supposed to be. What differences should I look for to distinguish which process was used?

Joshua Lee Beno
General Contractor Project Manager - Concord, California, USA
2007

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First of two simultaneous responses -- 2007

Dear Joshua
There are several California Hot Dip Galvanizers that do such a good job (bright, smooth zinc coatings), that hot dip galvanizing could easily be taken as electroplate. A magnetic thickness gauge can easily determine the difference. In hot dip galvanizing the coatings will be thicker than 2 mils (50 microns) whereas in electroplate the zinc coatings will be much thinner.
Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA

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Second of two simultaneous responses -- 2007

The thickness of the coating will be a fairly sure way to tell. If the zinc coating is about 10 microns its is most unlikely to be hot dipped galv. If its over 100 microns its almost certainly not electroplating.

Size of fabrication is a clue. Galvanizing tends to process much larger items (even up to 20m (60ft) in some plants), while few have electroplating facilities for items larger than a metre or two.

Another clue is drainage marks. Hot dip means just that - dipping in molten zinc. The liquid zinc runs off to the lowest point - drains off. And it is cooling as it flows, and eventually solidifying. So look for thicker coatings at lowest points, even perhaps stalactites where the last drip froze.

Further, it will have been suspended somehow in the molten zinc. Look for hook marks or wire marks, directly opposite the drainage marks above.

An another sign is to look for variable coating thickness. An item dipped with horizontal surfaces will not drain well and results in a thick coating. Electroplating tends to be very even coating thickness (but thinner).

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

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2007

Electroplated galv materials will have a much smoother brighter finish than a hot dipped galvanized. The galvanizing on hot-dipped steel will be up to 10 times thicker and much harder than electroplated material.

There is much debate about hot-dipped vs. electroplating in the construction industry. Fasteners, especially those used in coastal areas should be hot-dipped rather than electro galvanized, mostly because the installation process will gaul the softer zinc coating on the electro plated hardware. This will leave exposed steel which will stain the finished product in time.

For the majority of exterior applications, the Owner should insist on a hot-dipped product, for interior products (such as galvanized conduit and device boxes) there does not seem to any advantage to hot dipped galvanizing, and in fact many of these product are going by the wayside due to environmental air quality laws and laws limiting the amount of lead in building materials.

Scott Klosterman
contractor - LA, California

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Thanks for the feedback, Scott. I think your conclusions are correct but I think the big difference between electroplated and galvanized coatings is the thickness. A galvanized coating, being about 10 times as heavy as an electroplated coating, is far more suitable for exterior use but generally unnecessary for interior use.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

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2007

Dear Scott,
Many hot dip galvanizers use LEAD FREE ZINC.

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA