Powder on the Seacoast

Q. We are a building contractor and we have some of our steel components powder coated. We recently did a job with some powder coated aluminum handrails to a building situated on a seacoast installation. 

After about 18 months of exposure, the powder coating has deteriorated and broken down. There are areas where the coating is blistering, and exposed metal is beginning to rust. Can you give us any advice or information as to why the coating may have broken down in such a short length of time? —S.B.
 

A. Application of a coating is a process—a series of steps needed to achieve desired outcome. The quality that is expected in the field and the environment that a product will be exposed to after coating has a profound impact on the steps in the coating process. For example, if the product is a low-cost, institutional chair that will always be used indoors and has low quality demands, the coating process may be as simple as washing and applying a single coat of a hybrid powder. But if the coated part is going to the seacoast and the coating will need to survive in that environment for an extended period of time, the process is much more involved. Metal preparation must be virtually flawless. Blasting to remove all inorganic contamination (rust, scale, weld smut, etc.) is essential. The surface may also require some type of conversion coating, a chemical process that can enhance corrosion resistance. Multiple layers of coating, including a primer layer will be necessary.

I suspect that your coated rails did not receive the right process. They were probably coated with a fairly standard process of cleaning and coating that would be acceptable if the handrail was used inside, but not good enough for a severely corrosive environment. Check out the document located on the Powder Coating Institute website called Guidelines for Powder Coating Various Substrates. It includes a lot of information about how to attain a desired level of performance in a specific environment.