689 Chapter 28 Spray Technique Copyright Goodheart-Willcox Co., Inc. Triggering Triggering is a concept that is often difficult for the beginner to learn. Proper triggering involves releasing the trigger at the end of the stroke and pulling the trigger just before the stroke begins. Pull the trigger in one smooth, fluid motion. Pull too slowly and the spray pattern can be too heavy and run. Pull too quickly and the pattern may not fully develop. Triggering is especially important when a panel is painted in sections. For example, Figure 28-26 shows the spray pattern for a truck’s bed side. This long panel will be painted in three sections. The trigger is pulled at the beginning of each forward stroke and released at the end of each forward stroke. At the beginning of the return stroke, the trigger is again pulled. Releasing the trigger at the end of the stroke prevents excess paint buildup where the three sections meet/overlap. Trig- gering is not as important when the panel is short and does not need to be divided into sections. For example, a hood is usually painted in one section. Releasing the trigger at the end of the forward stroke will only prevent paint buildup on the masking paper that is protecting the windshield. Normally, the material adjustment knob is used to control the amount of paint discharged onto a surface, but skillful use of the trigger allows experi- enced painters to reduce the amount of paint applied without touching the adjustment knob. Simply put, partially pulling the trigger discharges less paint. When spraying a dry coat, for example, some painters will partially pull the trigger rather than change the fluid adjustment setting. This is an advanced technique. Match the Technique to the Job Different applications call for different kinds of paint coats. Several different types of coats are available to the paint technician. Often, paint manufacturers’ instructions will recommend a specific type of coat. The types of coating options available are explained below. Medium Wet Coat This is the most commonly used type of paint coat. To apply a medium wet coat with an HVLP spray gun, hold the spray gun 6″ from the surface. Your stroke should be 1 1/2 seconds/foot at a 50% overlap with the spray gun set at manufacturer’s recommended air pressure. The fan and material are set below maximum. For a conventional spray gun: 8″–10″ from surface, 1 second/foot, 50% overlap, spray gun set at manufacturer’s recommended air pressure, fan and material set below maximum. Basecoat should be applied in medium wet coats. When compared to a full wet coat, a medium wet coat puts less material onto the surface, dries faster, and is not as glossy immedi- ately after spraying. Full Wet Coat A full wet coat applies more material than a medium wet coat. A full wet coat will allow maximum flow out, increasing gloss. See Figure 28-27. This type of coat is difficult to apply to a vertical surface without runs. There are two ways to spray a full wet coat. The first way is to adjust the pattern control knob to decrease the size of the fan or adjust the material control knob to increase the amount of paint in the fan. Keep travel speed, distance, and overlap the same as a medium wet coat. The second way is to keep the fan and material settings the same, but move the gun slightly closer to the panel and reduce your spray gun Overlap Overlap Goodheart-Willcox Publisher Figure 28-26. A long panel can be sprayed in sections. There will be an overlap where the sections meet. Goodheart-Willcox Publisher Figure 28-27. A full wet coat of clear was applied to this vintage hood to achieve maximum gloss.