Mottling

A streaked spotty or striped appearance in a metallic colour.

Cause:

A. An uneven distribution of metallic flake caused by:

1. Using a spray gun that gives an unbalanced spray pattern.
2. Improper application technique such as tilting the spray gun during application, causing the spray pattern to become heavy at the top or bottom.
3. Holding the gun too close to the surface (flooding).
4. Uneven spray pattern overlap.
5. Omitting/Improper use of mist coats.

B. Too much thinner/reducer. Colour over thinned/reduced.
C. Applying clearcoat to a basecoat that has not thoroughly flashed/dried.
D. Improper application of basecoat (e.g. failure to apply or an improper use of a      low pressure mist coat, wet basecoat application).

Repair:

1. To uniform single stage metallic finishes, apply a higher pressure mist coat, panel by panel, while previous coat is still wet.
2. Or, allow basecoat colour to flash, and then apply a low pressure mist coat.
3. Finishes that have dried must be sanded and refinished. Caution: Large areas of basecoat must have clearcoat applied before sanding. However, small nibs or lint may be removed from basecoat by wet sanding, concentrating only on the defect. Apply additional basecoat to the sanded area before clearcoating.

Prevention:

1. Use recommended spray gun, including fluid tip and air cap for the material being sprayed. Always adjust the gun for best atomisation and balanced spray pattern before paint application.
   
2. Use the correct ratio of thinner/reducer.
3. Allow basecoat proper flash/dry time before clearcoating.
4. Follow basecoat application procedures.