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.
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.
And then there is price. The more you spend, the better the machining and interchangeability in the fluid-nozzle components and the better the atomization and flow. There are good all-around guns that have a single tip in the 1.7-1.8mm range that can be used to spray primer and a single or dual-stage paint job if cleaned and cared for. There are also kits that include two guns as a set with an extra nozzle to cover larger jobs and heavier paints with a smaller detail gun to hit under the hood, the wheels, and the doorjams. Detail work, custom paints, and a shop that uses high volumes of paints are going to require an expensive gun in the $500-$600 range. These guns are designed to use higher head pressures for better atomization and particle distribution while still keeping the TE up. Regardless, when we spoke to local painters, they were still impressed by the abilities of the $100 guns. The best way to decide is to ask the person who sold you the paint or a few reputable painters for their recommendations.
Air Compressors
For once, more horsepower isn't always better. In the case of air compressors and paint guns, you need volume and pressure instead. Paint guns are rated by the number of cfm delivered at a certain psi. For example, our Craftsman gun has an air-compressor requirement of 8.6 standard cubic feet per minute (scfm) at 40 psi. That means the compressor you pick must be able to produce that volume at that pressure consistently while you are using the gun. The rule of thumb we've repeatedly encountered is the compressor must produce 1.5 times the cfm that the gun requires at a given pressure (in this case, 12.9 scfm at 40 psi). Craftsman recommended its 7hp 60-gallon compressor that can deliver at least 12.4 scfm at 40 psi and 10.2 scfm at 90 psi with a maximum pressure of 150 psi. A compressor like this will cost around $500. The average $299 compressor is going to have trouble keeping up, forcing you to wait for the pressure to come back while parts of the paint dry. Not good.
Another hidden cost is the filter and regulator. Both are needed to keep debris out of the paint, and since our compressor can deliver over 100 psi of unregulated air, the regulator is mandatory to keep the inlet pressure below the required psi. Ask the paint-gun manufacturer about the recommended compressors, filters, and regulators required to run the gun before you buy it.
GUNS! Description PN Price Craftsman Heavy Duty High Performance gun 15519 $99.00 DeVilbiss Paint Gun Starter Kit 34566 $99.00