Primer is typically applied using a crosscoat spray pattern. A  crosscoat is one pass of the gun from left to right, followed  by another pass moving up and down. The starting direction  does not matter as long as the spraying is accomplished in  two perpendicular passes. The primer should be applied in  light coats as cross-coating is the application of two coats  of primer.  Primer does not tend to run because it is applied in light  coats. The gloss finish requires a little more experience  with the gun. A wetter application produces the gloss, but  the movement of the gun, overlap of the spray pattern, and  the distance from the surface all affect the final product. It is  very easy to vary one or another, yielding runs or dry spots  and a less than desirable finish. Practice not only provides  some experience, but also provides the confidence needed  to produce the desired finish.  Start the practice by spraying the finish coat material on a flat,  horizontal panel. The spray pattern has been already adjusted  by testing it on the masking paper taped to the wall. Hold the  gun 8–10 inches away from and perpendicular to the surface.  Pull the trigger enough for air to pass through the cap and start  a pass with the gun moving across the panel. As it reaches  the point to start painting, squeeze the trigger fully back and  continue moving the gun about one foot per second across the  panel until the end is reached. Then, release the trigger enough  to stop the paint flow but not the air flow.  [Figure 8-12] The constant air flow through the gun maintains a constant  pressure, rather than a buildup of pressure each time that the  trigger is released. This would cause a buildup of paint at the  end of each pass, causing runs and sags in the finish. Repeat  the sequence of the application, moving back in the opposite  direction and overlapping the first pass by 50 percent. This  is accomplished by aiming the center of the spray pattern at  the outer edge of the first pass and continuing the overlap  with each successive pass of the gun.  Once the painter has mastered spraying a flat horizontal panel,  practice next on a panel that is positioned vertically against a  wall. This is the panel that shows the value of applying a light  tack coat before spraying on the second coat. The tack coat  holds the second coat from sagging and runs. Practice spraying  this test panel both horizontally with overlapping passes and  then rotate the air cap 90° on the gun and practice spraying  vertically with the same 50 percent overlapping passes. Practice cross-coating the paint for an even application.  Apply two light spray passes horizontally, overlapping each  by 50 percent, and allowing it to tack. Then, spray vertically  with overlapping passes, covering the horizontal sprayed  area. When practice results in a smooth, glossy, no-run  application on the vertical test panel, you are ready to try  your skill on the actual project. A quick check of the spray pattern can be verified before  using the gun by spraying some thinner or reducer,  compatible with the finish used, through the gun. It is not of  the same viscosity as the coating, but it indicates if the gun  is working properly before the project is started.  Common Spray Gun Problems Figure 8-12.  Proper spray application. D O N O T  AR C S T R O K E 8 to 10 inches Begin stroke, then pull trigger. Move gun in straight line. Release trigger before completing stroke. Arcing causes uneven application 8-12