Finishing System Durability

While the specific paint chemistry can clearly have dramatic impact on the durability of the finished component, the use of effective surface cleaning and conversion coating practices may actually have an even greater impact. If end users and coatings applicators are looking to improve paint adhesion and corrosion resistance, it is critical to consider the surface preparation of the component.

Q. In reading the Painting Clinic section of the December 2007 issue, I noticed the first two articles asked about epoxy coatings and durability. The first question also asked about abrasive blasting versus washing.
While the specific paint chemistry can clearly have dramatic impact on the durability of the finished component, the use of effective surface cleaning and conversion coating practices may actually have an even greater impact. If end users and coatings applicators are looking to improve paint adhesion and corrosion resistance, it is critical to consider the surface preparation of the component. Best regards, and continue the interesting column. D.F.

A. After 55 years in the coatings industry, I believe I have an excellent understanding of the associated problems. That being said, D.F., I can tell you that you are absolutely, positively correct in your statement about the effect of surface preparation (pretreatment) on paint adhesion and corrosion resistance.

When I ran the Coatings Lab at Westinghouse Research, I had the opportunity to evaluate every available organic coating over every available pretreatment. I did this because I recommended finish systems for the products manufactured and painted on more than 100 of our paint lines. These products were exposed to every conceivable environment in service. Although I can’t quote results by “Chapter and Verse” because they are the intellectual property of the company formerly known as Westinghouse, I can tell you that application and use of conversion coatings and phosphate pretreatments in organic finishing systems on metal products greatly enhances paint adhesion, corrosion and humidity resistance.

The problem is that some product manufacturers cannot afford, and in some cases do not want to pay, the extra cost involved in what I call proper metal pretreatment. In some cases they use an iron phosphate rather than a zinc phosphate. In others they abrade rather than chemically pretreat their products. Most likely they will eventually suffer loss of business due to customer complaints and in some cases business closure.