Hot dip galvanized surfaces are extremely difficult to overcoat with paint whether for aesthetic reasons or for additional protection.

True or False?

The successful painting of any surface is determined by the correct cleaning and surface preparation of the material onto which the paint is to be applied. If hot dip galvanized surfaces are adequately cleaned to remove all traces of oil and other contaminants, there is no reason why most paint types cannot be applied directly onto the galvanized surface. The secret to success is thorough cleaning. The surface of a hot dip galvanized coating differs somewhat from the texture of a steel surface. Adequate cleaning is, if anything, more important when paint is to be applied onto galvanized steel.

The processes of sweep blasting of the zinc or the provision of a zinc phosphate conversion coating are frequently implemented where heavy-duty paint systems are applied. In the case of normal decorative paints, these special requirements are not needed. Acrylics and vinyl's will provide excellent adhesion on galvanizing that has been adequately cleaned. An exception is the application of alkyd enamel paint directly onto a galvanized surface. Alkyd based paints can cause a chemical reaction which leads to saponification at the paint and zinc interface. If alkyd enamel paint is preferred, a prime coat must be applied prior to the application of the enamel paint. Among the best primers is the trusted and reliable calcium plumbate which adheres extremely well to zinc. Overcoating of this primer should take place as soon as possible after it is applied since it is very sensitive to UV attack.

Many so-called experts recommend that a galvanized surface should be allowed to weather before a paint coating is applied. This concept can be successful in a benign environment where the degree of atmospheric corrosion is low, but the best results are achieved if a compatible paint coating is applied onto adequately cleaned hot dip galvanizing shortly after the galvanized coating has been applied.

While a total paint system, applied immediately after galvanizing, will provide the best results where ultimate exposure is required in an aggressive environment, the primer coat, at the very least, should be applied in factory conditions in order to ensure adequate zinc surface preparation, and also to prevent subsequent contamination of the galvanized coating.

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