References cited in this section

48. K.B. Tator, Organic Coatings and Linings, Corrosion, Vol 13, ASM Handbook (formerly 9th ed., Metals Handbook), ASM International, 1987, p 399-418

50. N.C. Fawcett, Polymer Mater. Sci. Eng., Vol 53, 1985, p 855-859

51. R.A. Iezzi and H. Leidheiser, Jr., Corrosion, Vol 37, 1981, p 28 Painting With Zinc-Rich Paints

Zinc-rich coatings, often called zinc-rich primers, are a unique class of cross-linked coatings that provide galvanic protection to a ferrous substrate. As the name implies, the binder is highly loaded with a metallic zinc dust pigment. After the coating is applied to a thoroughly cleaned substrate, the binder holds the metallic zinc particles in contact with the steel and with each other. Thus, metal-to-metal contact of two dissimilar metals is made, resulting in a galvanic cell. In this couple, zinc becomes the anode and sacrifices itself to protect the underlying cathodic steel.

The major advantage of corrosion protection using zinc-rich coatings is that localized pitting corrosion and subfilm corrosion are eliminated, even at voids, pinholes, scratches, and abrasions in the coating system. This cannot be said of any other type of protective coating, and it is this protective capability that makes zinc-rich coatings unique and widely used.

This advantage, however, comes with certain disadvantages. The underlying steel substrate must be cleaned of all rust, old paint, and other contaminants that may interfere with metal-to-metal contact. Thus, the degree of surface preparation must be quite thorough: blast cleaning should produce a Commercial Blast Cleaning minimum and, for immersion service, a White or Near-White surface. The Steel Structures Painting Council (SSPC), NACE, and other organizations issue standards for the surface preparation of metals for organic coatings: these are discussed in more detail in Ref 48 and also mentioned below.

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