Spraying Made SimpleComments (0)
This article is from Issue 46 of Woodcraft Magazine.
The right setup and spraying sequence are the keys to success.
By Keith Cochrane with Joe Hurst-Wajszczuk
As most professional woodworkers know, spraying is just about the fastest way to apply a finish. Done properly, it’s also one of the cleanest. A spray gun can quickly lay smooth coats on flat surfaces without leaving a stray bristle behind, and it can effortlessly apply finish into corners and crevices that would frustrate the best brush.
Back in the days of solvent-based lacquers, spraying was too much hassle for many garage and basement woodworkers to consider. Since then, advancements in waterborne finishes, coupled with a wide array of affordable spray guns, have put this professional finishing solution well within reach of almost everyone.
Using a spray gun is easy once you understand the basics. In this story, we’ll show you how to prepare your workspace, your finish, and your gun, and how to finish a door and cabinet in the proper step-by-step sequence. As with any technique, practice makes perfect. Invest a day or two spraying a few workshop cabinets, and you will soon have the skill to tackle other projects.
Note: The following steps focus on spraying waterborne finishes. If you plan to spray lacquer or other solvent-based finishes, you’ll need to take additional fire-safety precautions.
Before you can start spraying, you’ll need to do a little prep work to ready your shop, your finish, and your gun.
Set the stage
Cut the dust. A few specks of dust can ruin an otherwise flawless finish. Vacuum your space and project. If you don’t have a dedicated finishing room, you can use plastic sheeting or a canvas tarp to create an area that’s suitable for spraying. Cover any walls, floors, and machinery that might suffer from overspray.
Establish good airflow. Your goal is to stand in clean air and to direct overspray away so that it won’t be inhaled by you or settle on your project or other items in your shop.
The best approach is to use a high-powered commercial fan located behind filters to exhaust the overspray outside as you shoot. However, even a regular box fan covered with a filter will work, just not as well. Keep in mind that you need fresh “makeup” air coming in, which can be provided by an open window at the opposite end of a garage or basement shop. To allow you to consistently shoot toward your fan, set up a support turntable that permits you to rotate a project as necessary while you work.
Light it right. Reflective lighting is indispensable for exposing flaws such as drips, specks, or missed spots. Position the light so that you can see its reflection in the wet finish. Work lights with either fluorescent or halogen bulbs function well, though the latter can burn you if you bump into them.
Prepare the finish
Finishing products may have undissolved lumps or contaminants that can spoil a finish or clog the gun. After stirring well, pour your finish through a paper strainer (Woodcraft #151299), to catch these potential troublemakers.
Stains and waterborne finishes formulated for spraying don’t require thinning, but some latex paints may. If your sprayer comes with a viscosity cup, measure the time it takes for the cup to drain, and compare that with the manufacturer’s recommendations.
Setting up the gun
Air caps can be set in three positions–each one creating a different fan pattern. To change the spray pattern, rotate the air cap. The horizontal fan pattern is good for spraying cabinet and furniture sides while moving the gun up and down. Use the vertical fan pattern for tops or for other applications that dictate moving the gun from side to side. The round spray pattern is used to minimize overspray in tight spots or to better target small objects.
To set the correct fluid volume, first close the fluid knob control. Then pull the trigger and back off the screw until you get an even, wet coat without drips or mist.
Note that fluid volumes for vertical and horizontal settings are about the same. If you switch to a round fan pattern, you’ll need to reset your gun for less volume.
Smooth, consistent finishing requires a plan. The rule of thumb when spraying is to progress from the least visible to the most visible sections. This approach minimizes the amount of overspray that settles on top of surfaces that matter most.
3 Spray the outer faces. Set the air cap for a horizontal spray pattern. Start spraying a few inches below the cabinet, and move up the face, maintaining the same spray angle and distance from the beginning to the end of the pass. Release the trigger a few inches past the top of the cabinet. Repeat the up and down sequence, overlapping each previous pass by about 50%, until the side is covered. Rotate the cabinet as you work, so that you are always spraying toward your exhaust fan.
4 Finish the face frames. With the air cap set for a horizontal fan pattern, reduce the spray pattern either by reducing the fluid volume or by moving the gun closer to your work. Hold the nozzle perpendicular to the face frame, but angle the case slightly so that the spray hits the inside edge and does not deposit any overspray on the cabinet’s outer face. As when spraying the cabinet sides, begin and end the pass slightly past the ends of the face frame.
These photos focus on the front face of a door, but you’ll actually want to finish its back first, following this same three-step sequence. If time allows, let the back dry before tackling the front.
1 Start with the outer edges. Set the air cap to a vertical fan pattern. Hold the gun about 8" away from the door, and spray all four outer edges. Begin spraying a few inches before the wood and continue spraying a few inches after the wood.
2 Spray the inner edges. With the air cap set to a vertical spray pattern, hold the gun as shown and make a pass across the edge. To avoid laying too much finish on the center panel, position the gun so that the fan pattern is half on and half off the work. Rotate the door as you work to hit each frame part from the same angle. Pay attention to the inside edges, keeping the gun moving to avoid finish buildup there.
3 Finish with the panel and face. With the gun still set for a vertical spray pattern, hold it between 45° and 90°, and spray from side to side, pulling the trigger a few inches before and releasing it a few inches after each pass. Overlap each previous pass by about half the width of the fan pattern. Plan on a second coat for complete coverage.
If you leave finish in the gun, it can harden in the cup or nozzle, rendering the gun temporarily useless. The gun can sit idle for a coffee or lunch break, but if you plan to step away for more than a few hours, clean out the cup and run soapy water through the gun.
Remove the air cap and needle and let them soak in soapy water. Clean the cup thoroughly, including the gasket. Spray undiluted cleaning solution (such as Simple Green) through the intake hose until foam comes out of the nozzle.
For a complete gun-cleaning regimen, see “TLC for your HVLP” in Issue 33 (Feb/Mar 2010). The downloadable version (#150848D) can be purchased at woodcraft.com.
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