Buy all the gun you need and still have money left for glittery paint when you knowRattle-can primer is the easy way out. Sure it hides the engine-oil blow-by and road detritus, but you have to admit, the guy with the smooth colored fenders is the guy who gets the most attention. And it's way cooler if you do it yourself.
By Douglas R. Glad
photographer: Douglas R. Glad
And that's exactly what we planned to do. But we needed tools for the job, like paint guns, compressors, mixing buckets, and stuff. It turns out that all these things are related, so it's important to know a little about what you're talking about to get it right. We ended up with three guns that were completely different but each useful in its own way. We primed them up and shot them to see how they work and picked up some useful info on the way. But first, here is a little background.
HVLP vs. High-Pressure Guns
Right up front we narrowed our paint-gun choices to the high-volume low-pressure (HVLP) guns used for automotive paints. They use low-pressure compressed air (about 10 psi at the head) to get up to 65 percent of the paint onto the surface. This is called transfer efficiency (TE). Early high-pressure guns bounced the paint or simply blew it into the air and could be rated as low as 25 percent TE, meaning 75 percent of the paint was ending up somewhere other than on the car. At $42 a pint, you want the higher TE rating the HVLP delivers.
Hey, we're learning so we used the Rambler wheels to test-fire the guns. Proper procedure is to keep the gun level, about 6-12 inches from the surface at a 90-degree angle. The tricky part is learning to let go of the trigger before the end of the stroke. | 
New guns require that you run solvent through them before painting. Mineral spirits work, but we used gun and equipment cleaner we bought at the paint store for $10.50. | 
We did not have an inline filter between the compressor and the gun so we picked up a cheapie water filter for five bucks. Permanent oil and water filter combos are available to plumb inline but can cost up to $100. The plastic one we bought should be thrown away after five uses. |
Nozzles And Feeds
There are a lot of painter preferences when it comes to guns. We had to dig deep to find the general rules regarding nozzle sizes, the types of feeds the guns use, and whether or not to buy a gun that costs more than $500.
Nozzle size is easy. In general, the heavier the paint, the larger the nozzle needs to be. For example, if you plan on shooting primer, use a gun that advertises a 1.8mm-or-larger nozzle. The range is 1.0 mm to 2.2 mm in theory, but we rarely hear painters speak of anything outside 1.2 to 2.0 mm unless they're using specialized paints. The lower end of the scale is for thinner materials like single-stage paints, metallics, and pearls. The smaller tip is finer and gives you a good dispersion of the particles and can be used for clearcoats as well. There might be a problem using a fine tip for both types of paint, so listen to the paint guy when you buy.
There are two kinds of feeds: the gravity feed and the siphon feed. This area is loaded with old-man theory and prejudice on which is better. We eked out a little real science that says the gravity feed uses less energy (air pressure) to deliver the same amount of paint, because it does not have to draw fluid and therefore is more efficient. They also use every drop of paint. Gravity guns can be more expensive but are helpful for painting in tight spaces where a hanging feed cup can whack your freshly painted surface. Also, gravity guns usually have a clear or semitransparent cup so you know when you are running low instead of risking a paint-flow interruption.
Siphon guns are tough (ours was metal instead of plastic), usually cheaper, and you can set them down anywhere. We also noticed the siphon feed cups were usually larger and carried more paint. You decide.