Anyone who ever has admired the perfection of a paint job on a classic car or the high-gloss sheen of a lacquered cabinet knows that it's tough to beat a sprayed-on finish. For years, spray finishing was done only by pros with expensive equipment and large spray booths to contain the dangerous fumes. Not so anymore. With the advent of HVLP (high-volume, low-pressure) sprayers and systems, perfect finishes are within the average woodworker's reach. Lowe's is happy to provide this information as a service to you.
Unlike conventional spray guns, HVLP systems use a large volume of air at a low pressure to apply the finish (typically less than 10 pounds per square inch compared with the 80 to 90 pounds used by conventional spray guns). Using lower pressure causes significantly less "bounce-back," or overspray, an unwanted side effect of high-pressure systems. This means that an HVLP system will direct the finish where you want it-on the project.
Experts refer to how well a finish sprays on as transfer efficiency. The transfer efficiency of a conventional high-pressure spray gun is between 20% and 45%. With an HVLP system, it's between 65% and 90%. The higher the transfer efficiency, the less finish you'll need for your project-usually one-fourth to one-half of that of a high-pressure sprayer.
There are two ways to achieve the benefits of HVLP spraying. One is to purchase a system that includes a turbine (to generate high-volume, low-pressure air), a spray gun and a hose. If you already have a compressor, the other option is to buy a conversion gun. A set of chambers, or baffles, inside the conversion gun changes the incoming high pressure to a lower pressure at higher volume. Note that a conversion gun needs a powerful compressor (at least 3 horsepower, with a minimum 20-gallon tank) to operate properly. You also will require a filter between the gun and the tank to remove any oil or water present in the line. To further reduce the risk of contamination, set aside an air hose to be used only for spraying.
When selecting an HVLP system or a conversion gun, you will need to know the types of finishes you'll be spraying (now and in the future), as well as their viscosity. Finishes typically are grouped into three categories: thin (clear stains and sealers), thicker (thinned latex and oil-based paints), and thickest (unthinned latex and oil-based paints and fillers). The packaging should indicate which finishes a system or gun is capable of spraying.
HVLP systems traditionally are rated by the number of stages involved. The more stages, the more pressure is generated. One- and two-stage units are best for thin finishes. A three-stage turbine, however, can handle most stains, varnishes and water-based finishes, although latex may have to be thinned.
Originally published in Lowe's Wood Post magazine. Copyright (Fall 2003) SPC Custom Publishing.