Ask the Expert Question-and-Answer Archive

by Ron Joseph

July, 2005

Why Measure Viscosity of a Paint Coating?

Q. I purchased an air compressor around 1986. It came with a non-bleeder spraygun. I just decided to use it for the first time (what's 20 years). The manual is vague. It said " Mix and prepare the paint according to the manufacturer's instructions. The use of a viscosimeter can be very helpful. Strain the material to be sprayed through a 60 to 90 mesh screen or equivalent." I am doing this mostly for the fun of trying something new. In what way would knowing the vicosity be helpful? Is it worth buying a viscosimeter?

A. Viscosity is a useful measurement when mixing paint for application. Some application devices do not work properly if the viscosity is either too low or too high. For instance, on printing presses, roll coaters, coil coaters, etc., the viscosity must fall within a specified range. For spray guns you will select a needle/orifice/cap kit based on the viscosity of the coating. Manual spray applications are not overly sensitive to the coating viscosity because the painter can adjust the spray gun parameters accordingly; however, on automatic coating production lines the viscosity must be maintained within a tight range to prevent too heavy or too light a coating film from being applied.

If you know how to set up a spray gun properly then you don't need to purchase a viscosity cup because you will adjust the spray gun setting according to how thick or thin the coating is. If you were working on a production line and wanted part-to-part consistency then I would suggest the use of a viscosity cup.

Best wishes,

Ron Joseph