Ask the Expert Question-and-Answer Archive

by Ron Joseph

August, 2005

Cratering of Paint for Automotive Painting

Q. Recently we were trying to get a corrosion preventive/slushing oil approved from one of the auto companies. Our product was rejected owing to its failure in the ED compatibility test due to cratering. It was showing more number of craters compared to that of the approved oil. Can you kindly let me know which property of the oil needs to be addressed in order to clear the test requirements. Do you think that reducing the surface tension of the oil will help?

A. The most probable cause for the paint craters is surface tension; therefore, in my opinion I would try to change the surface tension of the oil so that it allows the paint to properly wet the metal surface. I assume that you know how to measure the surface tension of the approved oil, in which case your goal should be to match your oil to the approved one.

Do the automotive companies first run the metal through a surface pretreatment detergent washer before applying the paint? If so, then perhaps your oil is not as easy to remove from the surface as the approved oil.

Please get back to me with more details if you are not able to solve your problem.

Best wishes,

Ron Joseph