Determination of Volume Solids of Paints and Coatings by Accurate Dry Film Thickness Measurements

A new method to determine the volume solids of paints and coatings based on the measurement of dried film thickness over a known area has been studied in this work. It was compared to the American Society for Testing and materials method D 2697-73 Volume Nonvolatile Matter in Clear and Pigmented Coatings. This method determines the volume of the dry film by application of the Archimedes buoyancy effect. In addition, the project was structured to extend the ASTM method to coatings systems used in the marine industry. The volume solids of several typical marine coating systems were determined using the proposed film thickness method as well as the current ASTM method. The type of coatings examined were ketimine cured epoxies, amine and amine adduct cured epoxies, polyamide cured epoxies, vinyl, chlorinated rubbers, alkyds, inorganic zinc-rich coatings, urethanes, and waterborne coatings. The film drying or curing conditions used were appropriate to the chemistry involved in the film forming process. The results indicate that the precision of the ASTM method is better than the precision of the film thickness method. This is primarily due to poor film uniformity. It was also shown that there is no benefit in time savings and sample handling in making volume solids determinations by the film thickness technique, when the manufacturers recommended conditioning schedule is used to cure the paint film. The ASTM Method, then is the preferred one. From the results of the work on this project, it is concluded that the user and the paint supplier must agree upon the curing or conditioning schedule, as the curing conditions can affect the volume solids values obtained.