April's Adhesion Problem


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Q. In the April issue there was a question about black paint having poor adhesion. You wrote about the oil absorption and bulking values of different pigments. I would have been interested in the gloss of his black paint. I have had problems when the gloss was a dead flat because it was difficult to determine the pigment solids. If pigment solids and the flatting agent were too high, the vehicle would not hold it together. Whenever I could, I would request the gloss to be at least three degrees, then we were able to help avoid this problem.


It has been a while since my paint selling days, so I know I’m rusty on my terminology. If the gloss is in the higher range in his coating, perhaps the material is too hard once cured and can become somewhat brittle, which would also affect adhesion. As you pointed out, your column is not for formulation of coatings, but it still is an intricate factor in solving application problems.  S.B.
A. You are right on the mark! Bulking values, oil absorption, percent solids and flatting agents are all related to the gloss of a paint, as well as the adherence of the wet paint and adhesion of the cured paint to the substrate. Your terminology is also right on the mark. Thank you for writing. I always welcome comments.