Every month, we take a common question about powder coating and get an answer from our resident coating expert, Bruce Chirrey. If you have a question for Bruce, please send it to firstname.lastname@example.org.
Question: How do I achieve a very thick coating on fence components that will be used outdoors in all types of weather?
Answer: There are two routes you can go to achieve a thick film coating. The first is to use a PVC powder coating. For a protective PVC coating, a primer must be applied first. If not, the PVC won’t adhere properly. When this happens, the coating can be peeled away from the metal part. After you apply the primer, the PVC powder is applied to a hot part until the desired mil thickness (usually 8-25 mils) is reached. The part is then reheated (typically to about 300°F) to achieve good flow over the entire surface. This PVC coating is not actually cured, as it is only melted enough to cover the part. It does not have the same characteristics as a fully cross-linked coating. The final coating is corrosion resistant, but not very tough. It won’t have good durability because it can be easily scratched and dented. This type of application isn’t recommended for high heat environments since the coating can be reheated and reflowed at higher temps.
The second route is to use a fusion bonded epoxy (FBE) coating. This is probably a better choice for fencing. The parts are heated to 400-450°F and sprayed. The powder is then allowed to cure in place. This technique will typically generate a coated finish that is 8-15 mils thick. The FBE finished part is very corrosion resistant and the finish is quite tough. However, since fence parts are going to be heavily exposed to sunlight, a second coat of polyester powder coating is needed to protect the FBE layer from sunlight degradation. This second coat is usually applied to a hot part that has already been coated with the FBE. After coating the heated part with polyester powder, a little added oven curing time will be necessary. This second coat can also be applied later, after the FBE coating has cured, but you may need to sand the FBE coating to insure good adhesion by the polyester top coat.
Thanks, Bruce! If you need help with your finishing results, please give us a call. Bruce and our other specialists can troubleshoot your process and help you get the best finishes possible. Contact us today.
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