Q: I get all my powders from the same West Coast supplier, but they surprised me today. I’m not sure if I am curing incorrectly or not, but their technical data sheet says: “Coat at room temperature, place in oven at 400°F. Leave in oven UNTIL the part being coated is also 400°F, then at that point set the cure time.”
Is that correct for most Main Street powders? Hobbyist powders seem to be 450°F flash, then typically 400°F for 20 minutes.
A: Your powder coating supplier is giving you the right information. Your hobbyist friends have steered you wrong. A thermosetting powder coating requires a specified amount of heat (temperature) for a given amount of time. Hence, when a powder coating supplier recommends 20 minutes at 400°F metal temperature, they are referring to after the part(s) has reached that temperature.
Think of the difference between a bike fender made of sheet metal and an alloy wheel. The fender may take 2-3 minutes to reach 400°F, whereas a hotrod alloy wheel may take 30 minutes to reach the same temperature. And remember the clock starts after the part reaches the specified temperature, not necessarily the when the oven recovers after the doors are closed.
I recommend using a non-contact infrared thermometer to measure part temperature. Crack open the oven door enough to point the IR gun at the part and start your timer after the part hits the target temperature.
Reader reply: Mind blown. However, for two coats like chromes/clears, it’s way different. Right?
A: Indeed, you are correct. It is best to undercure the first coat, then apply the topcoat and bake the two coats completely per the powder supplier’s specification. By underbaking the first coat, you ensure excellent intercoat adhesion between the layers. As for specifics on undercuring, I recommend an approximately 50% cure (half time at temperature).
Regarding clearcoat over a chrome-look powder, you are correct. It’s way different. In this case, if you undercure the chrome basecoat and then apply and fully cure the clear topcoat, you will observe a visibly reduction in the “chrome-look.” It’s due to the leafing aluminum pigments still being mobile during the clearcoat bake. Hence, you will have to fully cure the chrome basecoat before applying and curing the clear topcoat.