Things like humididty and temp can make some difference, but unless it's REALLY cold or hot, this probably is not the problem. I've never shot the SW primer, but am assuming that if mixed per instruction, it should behave ok. This brings me back to gun setup. Let's say the gun specifies a max inlet pressure of 29psi. This is pressure at the inlet with the trigger pulled. The pressure at the compressor is not a reliable indicator. Actually, a gauge at the gun is probably not as good as simply spraying some test patterns. If the air is too low, you can still get a very good fan shape, but you'll see pretty large speckles around the outside of the pattern. Turning up the air to the gun will make them get smaller and smaller until eventually more air will not produce further improvment. That's about where you should be. More air than this will simply fill the booth with paint and defeat the point of the HVLP. Also, I've seen a lot of folks hold the gun waaaay too far away. At about six inches from the gun's nozzle, the paint is at its most atomized. As it travels farther away from the gun, the little droplets will collide with each other and form very large droplets. Not good. It may seem like being far from the work allows you to paint quickly, but it produces a poor finish. What I'm trying to say here is that before we start blaming ventilation, humidity, temperature, mixing methods, product nuances, etc., that we consider the most common problem: spraygun technique. I really hope some of this info helps.
CJ
