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Paint/Protective Coatings Engineering: What type of paint and coatings work with galvanized steel?

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    • CommentAuthorzee
    • CommentTimeFeb 8th 2008
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    Types of Paints/coatings that have worked with galvanized steels are:

    Factory applied coatings include baked on powder paint, sprayed on chemically cured epoxy resins, electrostatically applied fusion bond epoxy and sprayed on coal tar or petroleum based enamel. Field applied coatings are usually brush applied enamels, mastics, polyurethane, reinforced plastics or epoxies.

    1. Zinc-rich paints: Zinc-rich paints have been known for their excellent paint adherence to both new and weathered galvanized surfaces. They have been used in US for more than 75 years due to their barrier and cathodic protection. In many studies, zinc-rich paints outperformed all other classes of paint. One of the main reasons for its success is that it has the same characteristics as the galvanized zinc coating. These paints synergistically combine with the desired properties of the metallic zinc coating. In addition, zinc-rich paints are widely used for repairing damaged galvanized coatings. These types of paints are often used alone but for a more attractive finish, a top coat is used.

    2. Aliphatic Polyurethanes: This is a two component system, generally applied over a polyamide epoxy primer. Aliphatic polyurethanes have superior weathering and chemical resistance with good adhesion and an enamel-like finish. This type of coating requires stringent application procedures. Currently, on the market, there are limited formulations for industrial aliphatic polyurethanes. The cost per gallon precludes the development and use of aliphatic polyurethanes for protective coating applications. However, in urethane films, excessive intra-film bubbling may occur due to carbon dioxide formation.

    3. Epoxy-Polyamide Cured: This type of epoxy would have excellent adhesion to any type of galvanized surface. However, since they are aromatic, they are not resistant to sunlight. Many times epoxy-polyamide cured coatings are used as the ‘tie coat’ and then an aliphatic polyurethane top coat is used. This type of system is considered to be a superior combination for barrier protection coating.

    4. Latex-Acrylics: Latex Acrylics are fast drying, water-based materials that have excellent adhesion, durability, and weathering characteristics. Usually this type of coating is used as a top coat. Not only is this type of coating suitable for new and weathered galvanized steels, it is environmentally friendly.


    Types of Coatings that have not worked with galvanized coatings:

    1. Alkyds are not commonly used over galvanized coatings. It is widely known that in wet areas of the world, zinc will produce an alkaline surface. If alkyds are used, the alkaline surface with moisture would cause saponification to occur which would result in premature peeling and flaking.

    2. Asphalts, a petroleum based product are also not recommended for use with galvanized steel.

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