Applying Water-Based Lacquer
The problem you're having with #1 is running or sagging. Try a wet on wet approach where you shoot 2 coats of 2 wet mils a couple of minutes apart, instead of a full 4 wet mils at once.
These are some variables to consider in the technique:
2. This sticky point is something you look for as a condition on the work as a function of the environment. Temperature, humidity, air movement and your gun and settings will affect it. You may have little control over these. What you can control is evaluating when that first tack coat is too thin (make another quick, misting pass) or too thick (let it flash longer before putting on the second tack coat and possibly make the second thinner since you already have 3mils down).
3. Raw, sanded wood will behave differently than sealed, sanded surfaces.
If you spend one hour in your booth concentrating on exactly how much you can put on a vertical surface before it runs and noticing how much time it takes before you reshoot and how much you reshoot, etc., you'll have the technique down. If you're nervous, just walk around your next 5 sided vanity and keep misting it as lightly as possible and you'll probably do fine, but at some point you'll be better off to set up some scrap vertically and get your wet mil gauge and your stop watch out.
My experience is there is no set amount that is right for everyone. Climate and the brand of lacquer and everything else come into play. I use waterbased lacquer (ML Campbell) and not getting runs is something that I adjusted into. It may take a while to get the feel, so practice on flat pieces, standing them up to dry. If you do get runs, the flat pieces sand a lot easier than raised panels. I've also found that a little bit of air circulation helps a lot (fan), and a good 75 degree temperature with lowest possible humidity. Here that's about 65 percent, and I'd like it lower.
The above is good advice. Here's some more. Try varying your fan pattern. If you're spraying the inside of a raised panel, set the gun on round pattern with reduced fluid amount. Same for edges. Open up the pattern with more fluid on large, flat areas. If you're using an HVLP conversion or conventional compressor driven gun, play around with the air pressure. Use as little as possible to atomize the coating and avoid orange peel. Above all, practice before going after a critical work piece.
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