Hi guys,
I missed how active this thread was and was just reading through the posts.
So far I've painted two wing panels from bare fabric, top-coated over aerothane on two ailerons, and top coated two sets of struts. The first wing panel has great color but the second one has a much better finish.
With Stewart System, the base "fog" coats are very important to create color saturation and to create the correct base texture. It's part color, part texture. If the fog coats are put on too heavy with each coat, the paint will not leave behind the necessary texture to hold the final, heavier, top coat without sagging. So it's a combination of the fog coats achieving full color coverage, the correct "1000 grit" texture, and they have to be sticky to the touch without transferring color to your knuckle when you touch them. After a day of painting my knuckles all have a spot of paint on them from testing each coat for readiness for the next coat.
My wings were done over the winter with two kerosene heaters in the garage, one in the paint booth and one in the area just outside the paint booth. I also warmed the house to about 74 degrees and then drew warm air from the house as the exhaust fan kept the paint booth clear. If I had the temp in the mid 70's I was lucky and it was usually right around 70. About five gallons of tap water was poured on the floor before each session to bring the humidity up and to keep dust down. The added humidity helps the paint to flow out a little better as I understand it.
It's really important to check your surfaces before starting each next phase of painting. The water borne covering will build up over a speck like Bob said, accentuating flaws. 320 grit sandpaper and red scotch brite pads are your friends! As is compressed air, maybe a vacuum with a clean brush head, those lint-free shop rags, and tack rags specific to water based paints. The EkoFill isn't as durable as the primer and top coats so don't sand over hard points, use the scotch brite pads. I would sand the open areas then use the scotch brite pads to work over the tapes and other hard spots. The primer is more durable, as is the EkoPoly but you still have to be careful over the fabric rivets. If you get the surface clean and work out any nubs then the next coat looks great. I didn't iron the tape edges as aggressively as the videos suggest, but definitely did use the iron to improve problem edges.
The trick is to keep everything clean, keep dust down during spraying, spray the fog coats thin so that the texture stays rough, let the paint set to tacky but not transferring when touched (if it dries beyond that, stop, let it fully dry then start from surface sanding/cleaning/etc and more fog coats before proceeding to top coat), and then the top coat has to have that three second sheen as you spray. It takes more paint then you'll expect to get that top coat to gloss but when it dries it doesn't seem as thick. It's a leap of faith to some degree, you feel like you're over-spraying but when you're done it looks awesome and doesn't appear too heavy.
I had some success re-spraying the top coat over areas that didn't gloss up but I was adding that extra paint right after I had sprayed those areas so they were still fresh/wet. Go slow and be methodical, if the gun and your technique aren't giving you the three-second gloss then open up your flow valve a little more, check the pressure is enough to atomize the paint, maybe slow down your motion a bit, increase your overlap, whatever it takes but don't just keep painting without making adjustments on the fly. If you do a few feet of wing and see you didn't get the gloss you can go right over it when it's still wet and the gloss will come. Also, there were spots that didn't gloss and so I sprayed some more paint on, they took their time but laid down and glossed as the paint flowed out and set.
If you get it just right it's glorious but remember, clean, light fog coats, and don't spray the next coat until the tack is just right (was twenty to thirty minutes or more at 70 degrees).
Keep in mind, the videos that show shorter wait times between coats were made with an older formulation of the coating which had a much shorter pot life. The current coatings have pot lives in the hours so don't rush each coat, wait for the tack to set and for there to be no transfer of paint but don't let it dry beyond that before spraying on the next layer!
And tell Andy I said hi when you speak to him, he's extremely helpful!