Painting Copper

Question:

Having been a longtime reader and contributor to your column, I know that I will get many useful answers to my question.

I am a trustee of my local Board of Education, and we have a 75-year-old building whose facade and copula are copper coated and painted with a lead paint. We are in the process of having the paint removed and the copper repainted. We are curious about the expected life of the paint application, and what is the best (paint) to use. J.B.

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Answer:

It is well known that many oxides of copper do not adhere well to the base metal. The cause of paint adhesion failures on copper is due to delamination of the oxide film from the metal. These oxides must be removed before painting. There are several ways to clean copper before painting. The best way to clean copper before application of organic coatings is the one that works for you. The choice will depend on a number of factors, including equipment availability and costs. To clean copper before coating, do one of the following:

• Bright dip the surface. This is usually done in an acid solution and is a standard plating operation. Don't try this at home.
• Mechanically abrade the surface by sanding, wire brushing, abrasive pads, etc., either manually or with power equipment.
• Abrasive-blast the surface using glass beads, plastic or other media.

Apply the paint immediately after cleaning. Although other materials will work, epoxy primers will develop maximum adhesion to copper. I recommend a two-component epoxy-polyamide primer. This will chalk on outdoor exposure and must be topcoated with a weather-resistant enamel. Architectural enamels are suitable for this application. Waterborne as well as solvent-containing paints can be considered. Modern paints should last 5-10 years before the need for repainting.

It is important that you note the following: Make sure that removal and disposal of the existing lead-containing paint is in compliance with environmental and safety regulations. You may have to employ a person certified for lead-containing paint removal to do the job.