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Uneven film thickness increases paint cost, extends flash time, and creates avoidable rework. A heavy area may sag, trap solvent, or require polishing, while a thin area can show poor hiding, dry spray, or color variation. Professional control begins by treating pressure, fluid delivery, fan width, distance, overlap, and travel speed as one system.
Build a Repeatable Starting Point
Use the nozzle size specified for the coating and confirm that the needle, fluid tip, and air cap are clean. Measure pressure dynamically with the trigger fully pulled. Static regulator pressure does not show the losses caused by hose length, fittings, filters, or compressor cycling.
When setting a lvlp spray gun, verify that the air supply can maintain the required volume during a full pass. Set the fan to a stable wide pattern, open fluid delivery to a moderate position, and record coating viscosity, reducer ratio, booth temperature, and material temperature.
Read the Pattern Before Painting
Spray masking paper for one second at the intended working distance. The pattern should be symmetrical, with controlled center density and gradual edges. Heavy upper and lower horns may indicate air-cap contamination or fan imbalance. A dense center usually means fluid delivery is too high for the available atomizing energy. A dry, grainy pattern may result from excessive pressure, low fluid delivery, high viscosity, or excessive gun distance.
Adjust one variable at a time. If several controls are changed together, the technician cannot determine which correction improved or worsened the pattern.
Balance Pressure and Fluid Output
Pressure breaks the coating into droplets, while the fluid control determines material volume. Excessive pressure can increase bounce-back and overspray. Excessive fluid with insufficient atomization creates coarse droplets, orange peel, and edge loading.
For an air spray gun, establish clean atomization first, then increase fluid output until the test pass reaches the required wetness. Do not use high pressure to compensate for an oversized nozzle or overly open fluid control.
Standardize Application Technique
Keep the air cap parallel to the panel and maintain the equipment manufacturer’s recommended distance, commonly around 150–200 mm for many refinish systems. Avoid wrist arcing because it produces a heavy center and thin pass ends. Begin moving before pulling the trigger, and release the trigger before stopping.
Use a consistent overlap suited to the coating. Basecoat often requires tighter overlap to stabilize color and metallic orientation, while clearcoat overlap must preserve a continuous wet edge without excessive build. At panel edges, reduce fluid concentration by feathering the trigger and slightly increasing travel speed.
Verify Film Build
Use test panels and wet-film gauges during process development. After curing, compare dry-film readings from upper, middle, lower, and edge areas. If readings vary beyond the repair specification, correct the setup rather than adding an extra coat based only on appearance.
Record nozzle size, pressure, fluid-control position, fan position, distance, overlap, pass speed, flash time, and material use per panel. A documented baseline allows different technicians to reproduce the same result and makes paint loss visible. Consistent film build lowers material consumption, reduces sanding and polishing, and improves first-time finish quality.
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