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Copyright © 2006
American Galvanizers Association. The material provided herein has been
developed to provide accurate and authoritative information about
after-fabrication hot-dip galvanized steel. This material provides
general information only and is not intended as a substitute for
competent professional examination and verification as to suitability
and applicability. The information provided herein is not intended as a
representation or warranty on the part of the AGA. Anyone making use of
this information assumes all liability arising from such use.
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The performance of hot-dip galvanizing and zinc-rich paint is often viewed as equivalent due to the false perception that all zinc coatings are "galvanizing" (e.g. zinc-rich paints are commonly referred to as "cold galvanizing"). The use of the word "galvanizing," to represent a family of coatings that use zinc as a means of corrosion protection, has falsely portrayed all zinc coatings as being equal with regard to their corrosion performance. This article will compare zinc-rich paints to hot-dip galvanizing, specifically the testing applied to support the comparison, and the ten characteristics that distinguish the two corrosion protection systems.
A: The
simple answer is yes. ASTM A 780 discusses three different methods to repair damaged or uncoated areas of galvanized steel. One of those methods is zinc-rich paint, which is classified as inorganic or organic, based on the material used to bind the metallic zinc dust particles together. Inorganic coatings can often provide adequate corrosion protection in a single coat, while organic zinc-rich paints are often top-coated with another layer of paint. Unlike other paint systems, zinc-rich paints exhibit limited cathodic protection abilities in addition to the barrier protection all paints provide. However, the cathodic protection is largely based on the amount of metallic zinc dust in the dry film and the applicator of the coating. Zinc-rich paints must be constantly mixed in order to maintain a homogenous mixture to promote metallic zinc dust contact once the paint is cured. The cathodic protection provided by zinc-rich paints is considerably less than the cathodic protection provided by the hot-dip galvanizing process.
