Back-To-Basics: Mottling or Streaking

Sometimes going back-to-basics can make the difference between a quality repair and a failed repair. When it comes to spraying metallic paint, there are some common mistakes that are easily avoidable and can have a huge effect on the outcome of the repair.

What is mottling or streaking? This is when the metallic particles in a refinishing material "float" together and can form a streaking pattern or "tiger stripes". One of the common causes of mottling is a spray gun being held too close to the surface causing the refinishing material to be applied too wet. Uneven film thickness can also be another cause of metallic build up in one area compared to another. Some other causes of mottling and streaking can be:

  • Dirty spray gun
  • Improper spray gun pressure
  • Spray angle
  • Improperly mixed materials

Mottling can be avoided by testing the spray pattern of the gun before spraying the panel. A test pattern will allow you to see if the spray pressure needs to be adjusted or if the fluid tip is functioning properly. Spray the refinishing material evenly while holding the gun 90° to the panel being sprayed to avoid excessive film build in certain areas of the panel. Make sure to allow proper flash time between coats according to paint makers recommendations. If mottling or streaking should happen while refinishing a panel, look up the paint makers instructions for how to correct any streaking in the final coat of base coat. These instructions may include spraying a "control" coat to correct the metallic orientation.

These are just a few examples on how mottling occurs, and how to avoid it. Always follow the paint maker instructions and standard operating procedures to ensure a complete, safe, and quality repair.

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