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Some of my customers have asked what kind of paint is best for coating hot-dip galvanized steel. Is there a specific type of paint I should be recommending to my customers?

Chinatown Park
Painted Duplex System

First, I would never recommend any specific type of paint to your customers because if they have a problem the first person they are going to blame is you. Since paint is not your specialty, leave the paint recommendations to your customers paint supplier. Having said that, many types of paint have been applied to hot-dip galvanized steel over the years. Some patterns have emerged with specific types of paint, with some types of paint working better than others.

In the AGA publication, Duplex Systems, you will find a table (Figure 1, below) that discusses the compatibility of 16 types of paint or other barrier coatings that have been applied over hot-dip galvanized steel. While this information should not be looked at as a recommendation, it can help your customer assist their paint supplier with choosing the best type of paint or barrier coating to apply over their hot-dip galvanized steel if they are looking for the increased corrosion protection offered by a duplex system. Remember though, the specific type of paint or other barrier coating that will be applied over the hot-dip galvanized steel is only part of the formula for ensuring a successful duplex system. The other part of the formula, and probably the most important, is the preparation of the galvanized coating prior to applying the paint. If the preparation of the galvanized coating is inadequate, it does not matter what type of paint your customer uses, it will begin peeling off the galvanized coating sooner rather than later. 

The AGA recently completed an instructional guide, Preparing Hot-Dip Galvanized Steel for Paint. The guide offers a detailed walk-through of the steps necessary to properly prepare a hot-dip galvanized coating for paint or other barrier coating and is available for download in pdf form. It can also be ordered with either CD or DVD with visual demonstrations. For more information on ordering your copy of this guide, please send an email to dbarlow@galvanizeit.org

Figure 1: Barrier Coatings Compatibility with HDG Steel

TypeCompatibilityComments
AcrylicsSometimesIf the pH of the paint is high, problems may occur due to ammonia reacting with the zinc
Aliphatic PolyurethanesYesIf used as a top coat for a polyamide epoxy primer, it is considered a superior duplex system
AlkydsNo
NoPetroleum base is usually not recommended for use on galvanized steel
BituminousYesUsed for parts to be buried in soil
Chlorinated RubbersYesHigh VOC content has severely limited their availability
Coal Tar EpoxiesSometimesRarely used, only if parts are to be buried in soil
EpoxiesSometimesIf paint is specifically manufactured for use of galvanized steel
Epoxy-Polyamide CuredYesHas superior adherence to galvanized steel
Latex-AcrylicsYesHas the added benefit of being environmentally friendly
Latex-Water-basedSometimesConsult paint Manufacturer
Oil BaseSometimesConsult Paint Manufacturer
Portland Cement in OilYesHas superior adherence to galvanized steel
SiliconesNoNot for use directly over galvanized steel, can be beneficial in high-temperature system w/base coat
VinylsYesUsually requires profiling, high VOC's have severely limited their availability
Powder CoatingYesLow temperature curing powder coating work exceptionally well over galvanized steel

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