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QUESTION

I am in the process of setting up quality control standards for my spray operators. Is it necessary to periodically check the wet mil thicknesses of the coatings my finishers apply? Do they need to perform these process checks on a daily basis?

ANSWER

Yes, it is very important to check for wet mil thicknesses at least once a day. Normally, a wet mil thickness is red on a scrap test panel at the beginning of the work shift. Some manufacturers require wet mils to be checked twice daily and recorded on a spray operator process log. If filters begin to load up, the flow rate or thickness of the applied coating will decrease. With airless and air assisted equipment, tip-wear will increase the flow rate and thickness of the coating. A change in the viscosity or flow-out characteristics of the coating will affect the amount of material that will be required to be applied to allow the coating to flow together successfully. If the coating is too high in viscosity, the spray operator may apply too much coating to wet out the finish film. This may require too much material and result in the coating being applied too heavily. Maintaining uniform wet mil thicknesses and the correct amount of coating to be applied is critical to prevent possible finish failures such as cracking or adhesion problems. Inconsistent wet mils can also influence the appearance of the coating. The gloss or color may not dry to the desired effect.

Ed. note: Phil Stevenson is the founder of the American Wood Finishing Institute (AWFI) in Vineland, N.J.