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FAQ: What is Galvanizing?
-- and what if the paint won't stick?

What is hot-dip galvanizing?

Iron and steel rapidly rust and corrode. An excellent way to deter rusting for a very long time is to hot-dip galvanize the parts, that is, to dip them in molten zinc (rather like dipping strawberries in chocolate).

Why is galvanizing such a good rust-preventer?

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"Hot Dip Galvanizing
A Guide to Process Selection & Galvanizing Practice"
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User's Guide to Hot Dip Galvanizing for Corrosion Protection in Atmospheric Service
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Galvanizing is a great rust preventer for several reasons:

What are the down sides of galvanizing?

Can galvanizing be reliably painted or powder coated?

Yes, galvanizing can be painted, but it may not be easy -- especially if painting was not anticipated when the parts were galvanized.

If you are a homeowner or hobbyist trying to paint a galvanized surface, the best advice (compiled from dozens of public forum threads on this site) seems to be: clean the surface with a scrub brush and a detergent like trisodium phosphate (TSP), rinse, neutralize the detergent and acidify/etch the surface with diluted vinegar, rinse, apply epoxy or a self-etching primer made specifically for galvanized surfaces; avoid alkyd paints

If you are a manufacturer, the above will not be good enough! The best plan, used by auto manufacturers, is to employ galvanneal steel rather than galvanized steel if you intend to paint it. Galvanneal has been annealed after galvanizing in a way that causes the steel and zinc to interdiffuse so that you are painting a steel alloy rather than pure zinc.

Manufacturers may also wish to skip the chromate final dip if the parts will be painted because the brightness this dip imparts will not be required for painted parts. In any case, the galvanized or galvannealed steel must be phosphatized before beginning the painting process.

For detailed information on painting galvanized steel, manufacturers and specifiers should see "Duplex Systems: Painting Over Hot Dip Galvanized Steel", which can be downloaded as a '.pdf' file free from the AGA at www.galvanizeit.org/aga/aga-publications/download/non-member/931
www.galvanizeit.org/education-and-resources/publications/painting-hot-dip-galvanized-steel-1992
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This is only a very brief intro to galvanizing. Here is a partial list of related threads/ letters on the Finishing.com Hotline public forum:


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