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Spray pattern diagnosis is one of the most important skills in automotive refinishing. A painter who can read a spray pattern can solve defects before they reach the vehicle. When I see dry spray, tiger striping, orange peel, or uneven clear texture, I start by checking the pattern rather than immediately changing reducer or blaming booth temperature.
A lvlp spray gun Professional Automotive Tools setup should produce a balanced fan with fine, uniform atomization. To test it, hold the gun square to clean masking paper at normal spraying distance. Pull the trigger fully for one short burst. Do not move the gun during this test. The pattern should appear symmetrical from top to bottom, with no heavy crescent shape, split center, or dry broken edge.
If the pattern is heavy on one side, inspect the air cap first. Dried clearcoat or primer in one horn hole can push the fan to the opposite side. Remove the air cap and clean it with approved solvent and soft cleaning tools. Never use hard steel wire to open precision holes because it can permanently alter airflow. If cleaning does not correct the issue, rotate the air cap 180 degrees and test again. If the defect follows the cap, the cap is the problem. If not, inspect the nozzle and needle.
A split pattern usually means too much atomizing air, insufficient fluid, or excessive fan width. Reduce fan slightly or increase fluid output in small increments. A center-heavy pattern may indicate too much fluid, low pressure, or material that is too thick. Always adjust one variable at a time and record what changed. Professional painters troubleshoot through process, not guesswork.
Pressure loss is another common issue. The wall regulator may show adequate pressure, but the gun may receive less pressure after the hose, filter, and couplers. Check pressure at the handle with the trigger pulled. Also inspect the compressor capacity. If the compressor cannot keep up with demand, atomization may weaken during longer passes across hoods, roofs, or van panels.
Material preparation also affects the pattern. Strain all coatings, mix accurately, and use the recommended reducer speed for booth temperature. Viscosity that is too high can create coarse droplets, while over-reduced material may increase runs and reduce coverage.
A clean and correctly adjusted air spray gun allows the painter to control the wet edge, film build, and final texture. Pattern testing takes less than a minute, but it can prevent sanding and repainting an entire panel. In a professional body shop, the test pattern is not optional; it is the first quality inspection before the job moves to the vehicle.
