Wet Film Thickness gage Measuring the film thickness immediately after coating the surface is important to control the spreading rate and the final dry film thickness. Applying too much paint is an added expense without improving the physical properties of the coating. Wet film thickness should be monitored frequently to maintain an efficient coating process. A wet film thickness gage is an inexpensive, easy to use device. They cover a wide wet film thickness range from industrial maintenance applications to thin coil coatings. Wet film gages can be used on virtually every substrate.