Dirty Finish

Q. I am having a problem with the powder coating looking like it has dirt in it. You can rub your hands across the surface and feel the imperfections. The part was a chrome valve cover (brand new) and was pre-heated before powder was applied. R. G.

 

A. Have you ever heard the expression: “If it walks like a duck and quacks like a duck it must be a duck”? It applies here. If it looks like dirt and feels like dirt, then it must be dirt. The best way to tell for sure is to look at the defect under magnification. If it is a different color than the powder coating, then it is a foreign substance (dirt). You might even have to cut the particle open to see what is inside. If it is the same color as the powder you are spraying, then it is either caused by gun spits, low film build, or impact fusion.

The good news is, the solution is the same no matter what it is: sand the part and completely re-coat and cure it again. Be sure to get the surface absolutely clean, and eliminate dirt and contaminant sources in your spray area. Clean the gun, feed hopper, feed hoses, and feed pumps, as well. If you are using reclaim, make sure it is not contaminated either, or you will end up with the same result.

Remember this saying: “Cleanliness is next to Godliness.” In powder coating it is more appropriate to say: “Cleanliness is necessary for good surface appearance.”