Moisture Level in Compressed Air for Spray Painting

Question:

What is the maximum recommended compressed air moisture level for painting today’s high-tech paints in the automotive refinishing industry? Most paint manufacturers specify clean dry air, but most do not go as far as to define exactly what is considered “dry air.” As an engineer, for a supplier of air drying equipment, I’m very surprised that the paint manufacturers do not have very specific recommendations concerning this issue, which is critical for proper application and curing of these high-priced finishing materials. Please let me know what your recommendations are and if you are aware of any published levels by any major paint manufacturer or any other industry related organization. A.G.

Answer:

It is well known that air used for powder coating and for spray painting materials that are moisture sensitive must be dried by refrigerating, deliquescing or desiccating to remove moisture. Although they may exist, I don’t have references to the quality of compressed air to be used for spray-painting high-tech materials. The recommended moisture levels would apply to OEM as well as refinish paints. I recently recommended paints and painting procedures for refinishing a steam locomotive at the Railroad Museum of Pennsylvania (www.pfonline.com/articles/clinics/1001cl_paint1.html). The recommended paint system was essentially a two-component epoxy primer topcoated with a two-component polyurethane enamel (both high-tech materials). The paint data sheets show explicit details about application equipment, procedures and application temperatures. However, there is no mention about the compressed air quality. Since I am not in a position to recommend a specific moisture level for spray gun compressed air, I suggest you contact high-tech paint suppliers for their recommendations. Paint suppliers are listed under Coating, on pages 286-288, of the Products Finishing 2004 Directory and Technology Guide (www.pfonline.com/suppliers.html).