Coating Options for Steel

Q. We manufacture steel and aluminum mounting structures that are used to support solar panels in a variety of environmental conditions. Historically, we have used powder coating for the steel items, but we are now redesigning this line of products and assessing using structural steel members instead of hot- or cold-rolled sheet metal punched/formed as needed. The powder coating is not giving us as much protection from rust as we would like, and we have concerns about the prep that will be required from structural shapes. Hence, we are beginning to compare the benefits of powder with a wet-coat system.

We anticipate the need to coat several thousand parts per week while we are ramping up, but we do not have the ability to coat in-house, nor are we looking for that ability. We would prefer to find a company in the San Francisco Bay area that will be able to assist us in coating the components in volume. Where might I find information on wet-coat processes we might consider and compare to powder coat? —C.C.

A. If you are looking at liquid options to get better rust protection, you are chasing the wrong option. Liquid coating options will not enhance the corrosion protection just because it is liquid instead of powder. If you currently have premature corrosion problems it is because the process is flawed, not the powder coating. For structural steel in outdoor locations you need to do the right overall process whether it is liquid or powder. I would strongly recommend that you have the steel blasted, primed and top-coated. The blast operation will remove the impurities associated with rough-gauge structural steel (mill scale, carbon, rust, etc.) and provide a good anchor pattern for the coating. The primer should be a zinc-containing material. This will provide good resistance to moisture penetration, good corrosion resistance and good edge coverage. The topcoat should be a high-quality polyester material that will hold up in sunlight and provide further resistance to corrosion. The advice for liquid coating would be the same but it will probably cost more without providing the same corrosion resistance. You may also have trouble finding a qualified liquid coater in the Bay area due to limits on the solvent content of paint, but try looking for one on the Powder Coating Institute website, powdercoating.org.