Dirt lines are very fine lines up to 1 mm wide in the painted surface where the paint film is removed from the surface to varying depths. In the worst case the primer is exposed. One or more lines can occur running in the rolling direction and can be intermittent or continuous on one or both surfaces.
1. Dirt caught between the applicator roll and strip. This dirt rubs the wet paint film off between the applicator roll and the back up roll.