What causes Dry Spray?

A dry spray finish is characterized by a rough, almost sandpaper texture. It can be caused by several things including the coating, setup and technique. Listed below are the most common causes and the method of correcting them.

Atomizing air pressure too high - Air pressure that is too high for the volume of coating being supplied will create paint droplets so small that the much of the solvent easily evaporates. The coating does not flow with the lower solvent content. In addition, the increased air pressure causes additional bounce back which adds to the problem. Use the minimum air pressure required to achieve the atomization required.

Fluid pressure too low - Fluid delivery that is too low for the atomization air supplied will be over-atomized. This is common for heavier materials used in suction and gravity feed guns. The coating may need to be thinned. Consult your technical data sheet.

Gun too far from the part - If the spray gun is held too far from the part for the gun type, solvent has increase time to evaporate. Proper distance is as follows:

HVLP 6-8 inches

Air Spray 8-10 inches

A/A Airless 10 - 12 inches

Airless 12 - 14 inches

Spray booth velocity too high - A spray booth operating at a high velocity (greater than 150 feet per minute [fpm]) will cause the solvent to evaporate too quickly, not allowing the coating to flow. Typical booth velocities are in the 100-150 fpm range.

Spray booth velocity too low - A spray booth operating at a low velocity (less than 100 feed per minute [fpm]) will allow overspray from the gun to float around in the booth and land on finished parts.

Dry overspray from adjacent surfaces or parts - Use technique that does not allow overspray from the part you are spraying or adjacent parts to land on what has already been finished.

Gun speed too fast - Operating a gun at a high speed typically results in a film build that is too thin, not allowing the coating to flow. Typical hand speed for air atomized guns is about 3 feet per second.

Low booth humidity - A very dry booth will allow the solvent to evaporate sooner than desired. Consult your Technical Data Sheet for the proper type and amount of retarder to be added.