I have chronically had "fisheyes" or depressions form in my paint projects. They are not pin-holes caused by voids in the underlying strata but are shallow craters in the paint film.
This has been an ongoing problem in gel coat at another facility and was a problem recently in polyeurethane at my new facility.
Following the advice here and other sources, and installed a brand new, world-class compressor / air / paint system with more than 40 ft of iron pipe to the gun, in-line water traps and drains, sub-micron coalescing air/oil filters, a paper roll filter just before the dedicated "painting only" hookup, a new air hose and finally a new "tennis ball" filter at the gun (a new Finish Line III).
I live in high and dry area of southern Calif. and have never seen any moisture/oil beyond the first in-line pipe drain 10 ft from the compressor. Still apparent contamination issues.
The craters show up in the surface well above the original strata so I do not believe it is contamination in the surface being painted but am at a total loss to explain their origin.
Could the paint be inadequately mixed? I am aware that gelcoat (polyester paint) topcoats have wax in them to seal the surface. Could the wax coalesce in the paint to form immiscable droplets?
Thanks for the forum. I have lurked a long time and it is a great resource!