Metal finishing Q&As since 1989

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Inquiry of galvanized vs zinc finishes

I am looking for a u-bolt for a boat trailer. What is the difference in: zinc plated; hot dipped galvanized; cold dipped galvanized.

Debra Burnum
consumer - Crawfordville, Florida, USA
2004

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The difference between hot-dipped galvanized finishes and zinc plated finishes was already answered in detail on the Hotline-letter that brought you here: so to avoid rehashing everything, I'll just say that galvanized finishes are much heavier so they will protect much longer.

But 'cold dipped galvanized' is a term I have never heard, and it is perhaps simply a sales term invented by one vendor. I suppose it could mean zinc plating since that is done at about ambient temperature, or it could mean mechanical plating / mechanical galvanizing which is a cold, mechanical process that coats a part with a layer of zinc that is heavier than electroplating but usually lighter than hot-dip galvanizing. Go for the galvanized, Ms. Burnum.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004

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"Cold Galvanizing" and similar terms are often used in the UK (and elsewhere) to mean Cold Galvanizing Compound / Zinc Rich Paint. This does provide some electrolytic protection, but nowhere near as much as zinc metal applied as sprayed molten metal, plated of hot dip galvanized. As Ted says, the thicker the zinc the better the protection, and for this go galvanized (hot dip) every time. Zn plate is about 5-10 microns. Hot Dip Galvanised is usually over 85 microns - nearly ten times the protection. Only thin coating that comes close (about equal) is Zn-Ni electroplated, which has the advantage of thin coating, & smooth appearance.

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

2004