Coating Thickness Guidelines

Q. We are attempting to create a specification for our powder-coated products. The coating thickness varies on different products and in different colors. I am trying to determine what film-thickness range I should specify. Are there any guidelines for film thickness for a powder coating operation? –R.B.

A. Yes, there are some resources that can help you identify the correct film thickness. For a starting point, look at the powder supplier’s Technical Data Sheet (TDS), which should include a recommended range of film thickness for that particular powder. The range may be fairly broad, like 1.5 to 3.0 mils, but it will give you some idea of what thickness range will work. Coating thicknesses in this suggested range will provide the listed performance properties and will avoid unwanted appearance properties such as excess orange peel.

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Another key issue to consider is the desired performance you expect coupled with the environmental conditions that the part will be subjected to in its end use. The final factor for consideration is the nature of the substrate being coated. The shape and texture of the part will influence how much thickness will be needed and how tightly the overall average can be controlled.

Try to establish a minimum film thickness based on the powder’s hiding power and the performance needed. For parts with clean, smooth surfaces that will not be subjected to harsh environments, the TDS is a good source of guidance. Typically, a thickness of about 1.5 to 2.0 mils will work well. The more geometry you have on the part, the more variance you will likely have, as the part shape will affect the film uniformity.

For parts that must handle harsh environments, you may need more film thickness. Outdoor performance will require a thicker minimum, therefore a thicker average film build, say 2.5 to 3.5 mils. If the surface is roughened or blasted, you will need a higher average to make sure that the peak areas have sufficient coating. For extreme environments or very high performance, you may need two coats. Keep in mind that edge coverage is modest with one coat, and a second coat will provide much better protection at the edges. Also, a primer coat will provide a much better layer of protection from moisture. With a primer and topcoat the overall thickness could be 4 to 6 mils.

There is not a universal thickness that works for every situation. Check the TDS, consider the performance needed, look at the substrate, and you should be able to come up with the right specification.