CARB posts final report on relationship between volume percent of solids and hiding in arch. coatings.

"Correlation Between Solids Content and Hiding as it Relates to the Calculation of VOC Content in Architectural Coatings," the final report for a research project conducted for California's Air Resources Board (CARB) by Cal Poly, San Luis Obispo, has been posted at CARB's web site.

The project's goal was to determine the relationship between the volume percent of solids in coatings and the hiding of the coatings. The basis for the calculation of VOC content in paint rules ("VOC, less water and less exempts") is that there is a consistent relationship between solids and coverage, or hiding, especially in typical flat and non-flat house paints.

The researchers determined that although for a particular coating the hiding improves as the solids content increases, across different coatings, higher solids content does not necessarily equate to better hiding. In many cases, a 35% solids by volume water-based coating hides as well as a 60% solids by volume solvent-based coating. Accordingly, since the basis for using "VOC, less water and less exempts" was not supported by this study, this standard for the VOC content for house paints does not appear to be the ideal standard.

The researchers developed a different standard, termed "hiding VOC," which is defined as the amount of VOCs emitted by hiding (as opposed to simply covering) one square meter with a paint. Using this measure, among the flat and non-flat paints tested, solventborne coatings on average emitted over ten times as much VOC to hide the same area as the waterborne paints did, according to CARB.

The full report can be downloaded at the CARB web site: www.arb.ca.gov/ coatings/arch/whatsnew.htm.