If you are getting fisheyes when applying solvent based coatings with air spray equipment, the problem might be your air. Solvent based coatings will attempt to escape from any moisture droplets, causing fisheyes. Frequently, the contamination can be viewed in the center of the fisheye. So why is there water in your air? You might be surprised at how many paint shops don’t have a moisture and oil separator in the compressed air line leading to the paint booth. Of the shops that do have a moisture and oil separator installed, many are full of water or inoperable. I’ve been to plenty of shops where the painters aren’t even aware of the location of the moisture and oil separators or the required maintenance.
A good moisture and oil separator will remove moisture, oil, and particulate contamination. If you want to avoid fisheyes when using air spray equipment, clean air is essential. My favorite unit is from Binks DeVilbiss, model DAD-500. This is a three stage unit which utilizes a desiccant drier as the third stage. Remember that when the desiccant turns from blue to pink, it needs to be replaced.
If you suspect that you have moisture in your compressed air and want to test for it, follow the instructions of ASTM D4285-83(2018) Standard Test Method for Indicating Oil or Water in Compressed Air. This involves aiming the air stream only a white cloth or blotter paper for two minutes and then examining for the presence of contaminants.