Definition - What does Mottle mean?
Mottle refers to a type of corrosion defect that appears on a metal surface due to improper pigment application. It is characterized by a ring-like blotch of discoloration.
Corrosionpedia explains Mottle
The formation of mottles is due to an inadequate coating application on a metal surface. This is often due to inconsistencies in film thickness uniformity across the entirety of the metal surface being treated. It is more easily observed in lighter colored metallic finishes where color variations are apparent.
In cases where mottles are present, some parts of the metal surface are left without adequate pigment protection against corrosion due to low film thickness. As such, these areas are prone to significant corrosion and require additional protective measures. This can often lead to time, labor and cost intensive corrective actions being required.