Regulations, Violations, Permits, VOC, HAP and Such

Q: This question relates to situations in which a company is required to comply with a specific VOC limit for its coatings. Is there a short and simple method for determining if a mixed coating is likely to have been over thinned by the painter(s)? For instance, can one use coating viscosity or density to make a quick and dirty determination?

A: Viscosity is inversely proportional to temperature. As temperature increases, viscosity decreases; however, be aware that this is not a linear relationship. If you set up precise standards for different mixing ratios at a specified constant temperature you should be able to determine the viscosity at which the coating is likely to exceed the VOC limit. If you choose this method, be aware that you will need a sophisticated, sensitive laboratory instrument to measure the viscosity and I very much doubt that a simple Zahn cup will do the trick. Further, even if you can determine the viscosity at which the VOC is exceeded, this would not be legally acceptable for citing the company for non-compliance. The only legal method for determining compliance is EPA Method 24 which in itself comprises several ASTM methods, none of which includes viscosity.

In the case of plural component coatings, such as polyurethanes and epoxies, the problem becomes considerably more difficult, because the viscosity starts to increase immediately after the components are mixed. Initially, the viscosity increases almost imperceptibly, but as the coating ages the viscosity rises ever more rapidly until the coating becomes a solid. Moreover, the reaction time is also a function of temperature, with viscosity increasing rapidly as the temperature increases. Therefore, for plural component coatings it seems most unlikely that you would want to use viscosity as your "quick and dirty" tool to screen for potentially out-of compliance coatings.

Density is definitely a method that you could consider for screening both single and plural-component coatings. As with viscosity, temperature must be taken into account, but I don’t believe density is quite as sensitive to temperature fluctuations. With properly established standards it is possible that you can use this method to perform your quick and dirty screening.

Try both methods and see if they work, but always remember that the only legal method for determining compliance is EPA Method 24.

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