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March 7 - March 13, 2011

What is the effect on the permeability of a coating when you add additional coats, either at the time of the original painting or as a maintenance activity?

Selected Answers

From Joseph Schinner of Akzo Nobel Coatings Inc. on March 8, 2011:
Let's cut to the catch: Those who specialize in tank linings, corrosion protection, waterproofing, etc., with coatings where permeability is of the essence usually prefer multiple coating layers, even within the same coating type (situation dependent, of course). It was proven long ago in the field and in the lab that there is a synergistic enhancement with using 2 or more layers of the same coating. This is frequently superior to that coating at the same or even higher total film thickness as a single coat. Mutiple layers provide a predictability that minimize failure claims. This does not supercede or interfere with the need for primer with topcoat--and tiecoat where needed--but addresses layers within each function. Coatings companies are working toward technology that reduces layers and total DFT (dry film thickness) for competitive advantage with more or less success. Sometimes abrasion resistance can be enhanced the same way, proving that what happens at these interfaces carries over into other properties.

From VCBud Jenkins of CSCS on March 8, 2011:
The theory is that perms are time dependent and successive coats will not affect permeability unless they are of lower permeability. I think I should assign this project to a student at Cal Poly Pomona Paint Lab to see if it really is true or not.

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