How can I fix streaking, spottiness, or striping in my car’s metallic paint surface?

This condition is known as mottling. To fix it, apply a higher-pressure mist coat, panel by panel, while the previous coat is still wet. Or allow the basecoat to dry, then apply a low-pressure mist coat. Finishes that have dried must be sanded and refinished.

In this article, I’ll answer common questions about how to prevent mottling and eliminate it when it happens.

• What is mottling?
• What causes mottling?
• How can I repair a surface that has mottling?
• How do I prevent mottling?
  
  

What is mottling?

Mottling, also called streaking, tiger or zebra stripes, floating, or flooding, happens when the particles in a metallic finish float together to form a streaking or striped appearance.

What causes mottling?

Four reasons mottling occur include:

1. There is an uneven distribution of the metallic flakes. This could be caused by:
   • Using a spray gun that is producing an unbalanced spray pattern.
   • Using the wrong application technique, such as tilting the spray gun, resulting in the spray pattern becoming heavy at the top or bottom.
   • Holding the spray gun too close to the surface (flooding).
   • There is an uneven spray pattern overlap.
   • Mist coats aren’t used or are improperly used.
2. Too much thinner or reducer is used, resulting in the color being over-thinned or reduced.
3. Clear coat is applied to a basecoat that’s not thoroughly flashed or dried.
4. The basecoat is improperly applied. It may have not been applied a low-pressure mist coat or wet basecoat was used).
   
   

How can I repair a surface that has mottling?

Here are three tips for repairing a finish that shows signs of mottling:

1. To achieve uniform single-stage metallic finishes, apply a higher-pressure mist coat, panel by panel, while the previous coat is still wet.
2. Allow the basecoat color to flash or dry, then apply a low-pressure mist coat.
3. Finishes that have dried must be sanded and refinished. Caution: Large areas of basecoat must have the clear coat applied before sanding. However, small nibs or lint may be removed from the basecoat by wet sanding (concentrating only on the impacted area). Apply additional basecoat to the sanded area before clear coating.
   
   

How do I prevent mottling?

Steps you can take to prevent mottling from occurring on a paint finish include:

• Use the recommended spray gun, including the right fluid tip and air cap, for the material being sprayed. Always adjust the gun, testing it to achieve the best atomization and balanced spray pattern, before the paint application begins.
• Use the correct ratio of thinner or reducer.
• Allow the proper flash or dry time for the basecoat before applying the clear coat.
• Follow the manufacturer’s basecoat application procedures.

Following these tips will help you avoid mottling in your metallic finish.