Viscosity is a very important paint property, usually determined by measuring the time required for a given quantity of paint to flow through a hole in the bottom of a metal cup. A number of cup sizes and drain hole diameters are available for use with different viscosity paints. Three widely used viscosity cups are the Fisher, Ford, and Zahn viscometer. Table 10.1 gives conversion values for use with these cups.
It is important to correct the viscosity cup flow-out times for the temperature of the paint. The recommended spray viscosity is typically based on a temperature of 70◦F. If the viscosity is measured at a colder or warmer temperature, the actual viscosity could be too low or too high.Apaint supplier can provide the appropriate corrections for their product. Be sure that the type of Zahn cup or other viscosity cup used is consistent. In addition, be sure that the method of measurement is consistent. Some operators consider the first break in the paint to be the stop point, while others may wait until the cup is virtually empty.
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