Q. I am a quality control manager for a furniture manufacturer. We have been getting complaints about roughness in our topcoat. Under magnification, I was able to identify the cause of this problem as the presence of solid particles in the topcoat. My guess is that they are coming from sanding. Is it standard practice to allow sanding in areas where the final top coat is sprayed? Do finish manufacturers condone this practice? M.O.
A. The answer to both your questions is, “No!” No one condones this practice. A sanding operation should be nowhere near any organic finishing operation, whether it is application of a stain, primer, intermediate coat or topcoat. Any manufacturing operation producing particulate matter that can enter shop air should be as far away as possible from any fishing operation. Therefore, having a sanding operation anywhere near the topcoat spraying area is just asking for trouble. The same rule would apply even if the topcoat was applied by brushing.
In today’s factories, application of organic coatings is done in areas where the finishing material overspray and solvent vapors are exhausted to protect workers and the building itself. This is done mostly in spray booths equipped with exhaust fans. Make-up air for painting areas usually comes from within the shop and is not filtered, in most cases. There have been instances where airborne particulates generated from operations such as sanding hundreds of feet away have been drawn into spray booths. To compensate for this problem, appliance and automotive manufacturers use enclosed spray booths with filters to remove particulates from make-up air.