695 Chapter 28 Spray Technique Copyright Goodheart-Willcox Co., Inc. thinner flows out. The thinner can be directed into a paint mixing cup, if the cup needs to be cleaned out, or into the waste thinner barrel, Figure 28-41. Some painters leave thinner in the gun and seal the cup threads. This keeps the thinner in the gun and will help soften any hardened paint in the paint passages. If a disposable cup liner is used, the cup can be removed and thinner can be poured or squirted inside the gun. See Figure 28-42. Triggering the gun will allow the thinner to flow out. Once the cup has been emptied, remove the air cap from the gun. Use a WORKING SMART Spray Gun Cleaning Spray guns must be cleaned after every use. Spray gun cleaning is nonproductive time, but it absolutely must be done. A clean spray gun sprays better than a dirty gun. Paint flows better when passages inside the gun area are clean. Dried paint inside a spray gun may soften and spurt out with the fresh paint, contaminating the new finish. Waterborne paint and solvent paint cannot be mixed together, even as waste paint. Waterborne paint requires a dedicated spray gun to prevent a reaction between residual paint in the spray gun after cleaning and paint in the cup. Cleaning a waterborne spray gun may require a special cleaning solvent obtained from the paint manufacturer. A separate gun washer and liquid waste barrel is required for waterborne paint. Solvent Borne Cleaning Loading a spray gun with thinner and then spraying it out is not a recommended way to clean a spray gun because it puts VOCs into the atmosphere. See Figure 28-40. To manually clean a gravity-feed spray gun, first empty the paint from the cup. Load the cup about one- third full of clean thinner, install the lid, and shake the gun. This will allow the thinner to clean the underside of the lid. Trigger the gun (without air pressure) so NOTE Goodheart-Willcox Publisher Figure 28-39. When leaning over to paint the hood, a careless technician allowed the air hose to touch the wet clearcoat on this fender. Hose touched here Goodheart-Willcox Publisher Figure 28-40. Spraying thinner to clean the spray gun needlessly contaminates the air with VOCs. Goodheart-Willcox Publisher Figure 28-41. Load the cup with clean thinner and trigger the spray gun (without air pressure) over the waste thinner barrel to clean the cup.