Painting Galvanized Steel


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Q. We have been painting solar collector assemblies, not the collectors themselves, but the structures that support them. These structures are fabricated from galvanized and plain steel parts, depending on their location in the assembly. Under certain conditions, the paint must withstand temperatures up to 300°F for extended periods of time. We have been applying a low-gloss black enamel to these structures.

In this application the paint must last for several years in service without peeling, flaking or other deterioration. We have been getting customer complaints about paint peeling and flaking off the assemblies. What is the best way to solve our problem? B.W.


A. Your problem has a two-part solution. The first part is the choice of a suitable surface pretreatment and the second part is choice of a suitable paint. The best pre-paint treatment for both galvanized steel and plain steel in outdoor service is a zinc phosphate.

Since you did not describe the type of paint you are applying, I can't judge its suitability for this application. The best coating to use is a high- temperature, corrosion- and weather-resistant paint. These coatings are commercially available. Your present coating may have the required performance characteristics. Discuss this with your paint supplier and ask for a performance data sheet. Then ask if the paint can be applied direct-to-metal. If it cannot, it will require use of a primer.