Splotchy Appearance in Coating

We use manual spray guns to apply a textured powder over a cast part, and that black finishes have a dark/light, splotchy look to them after they are cured.How can wer get better appearance?


Facebook Share Icon LinkedIn Share Icon Twitter Share Icon Share by EMail icon Print Icon

Q. We use manual spray guns to apply a textured powder over a cast part, and the color that is the biggest issue is black. The problem is that the finish has a dark/light, splotchy look to it after it is cured. You can see the color variation at the booth, and it is still there after cure. Any suggestions on how we can get better appearance? J.P.

A. The appearance you describe as splotchy is most likely caused by the gun settings and application technique. The flow rate is the place to start. Adjust the powder flow rate and secondary air controls so that the powder is smooth and free from any surges at the tip. Adjust the air volume up and/or powder down until you are free of any surfing. Make sure the amperage and voltage are at the optimum level. Start with low voltage (65 or lower) and low amperage (20 or lower) and adjust down, if necessary, to avoid back ionization or up to improve charge efficiency.

Keep in mind that charging efficiency is partly related to gun-to-target distance, so you do not need high voltage for manual application at close range. Keep the gun at a consistent distance for the part and stroke the same way with slow, methodical passes in line with the length of the part. Match the pattern up to the size of the part. Avoid radical moves of the gun that change the pattern or the distance from target, the so-called “gyroscopic” style of coating. The combination a smooth pattern, low amperage and voltage, and a consistent stroke should correct your problem. 


  • Anodizing Vs. Powder Coat

    I am an engineer on a large yacht build project and urgently need information and advice on choosing a finish for the aluminum deck plates in the engine room.

  • Curing Oven Basics

    Simply heating up the substrate does not cure the coating. There are many variables to consider when choosing the best cure oven for your application...

  • Masking for Surface Finishing

    Masking is employed in most any metal finishing operation where only a specifically defined area of the surface of a part must be exposed to a process. Conversely, masking may be employed on a surface where treatment is either not required or must be avoided. This article covers the many aspects of masking for metal finishing, including applications, methods and the various types of masking employed.