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Home  >>  Products  >>  Film Thickness  >>  Wet Film Thickness

Wet Film Thickness (WFT)

Coating thickness measurement or Film Thickness helps monitor the paint process and maintain the appropriate coating properties for quality application. The measurement of the thickness of an applied liquid-based coating is crucial in application. The thickness of the coating affects the coating quality and its application costs. Measuring it and knowing which wet film thickness or mil gauge to use should be considered by all coaters. A wet film thickness gauge should be used to measure the film thickness as the coating is being applied. This is to ensure that the wet film measurement is in an acceptable range.
  • What is it?
  • Why it is important?
  • How to measure and calculate
What is it?
Wet film thickness (WFT) is the measurement of the thickness or depth of an applied liquid wet film, paint, or coating before drying occurs. The wet film of powder coatings can also be measured prior to curing. The proper film thickness has an impact on the opacity, appearance, and protective properties of the coating. Applying too much coating can also be detrimental and can lead to excessive cost, drying time, cracking, and flaking of the paint film.

Why is it important?
The thickness of a wet coating should be monitored frequently to maintain an efficient coating process. The wet film thickness measurement of a coating is important to production time and cost savings. Cost savings can be found by applying the least amount of a coating that achieves full coverage per a specified range. Measuring the film thickness also allows the applicator to test and adjust the film thickness to the target desired. For example, spray gun speed, number of passes and spray tips can be adjusted to apply the desired amount of coating to meet the specified dry film thickness, which can then be measured by a dry film thickness gauge.

How to measure and calculate?
Wet Film Thickness Gauges provide an inexpensive, quick and easy method to measure the thickness of coatings immediately after application to a substrate. They cover a wide wet film thickness range from industrial maintenance applications to thin coil coatings. Wet film gauges can be used on virtually every substrate. These gauges are also commonly known as: Wet MIL Gauges, Combs, Step Gauges, WFT Gauges and Notched Gauges.

This type of gauge has notches (or teeth) constructed into the sides of the gauge that are referenced to each other. The two outside notches are the same size and are used as a zero reference and reference the wet film. All of the other notches on the same side are shorter and reference the depth of the wet coating as well as the distance from the zero reference. These different distances represent the distance from the surface of the substrate to be measured and are graduated in MILS (0.001”) thickness and are also available in a micron scale. As an extra benefit some of these gauges can be customized with a company logo and information.

  1. Place gauge on wet film at 90° angle
  2. Press into film
  3. Withdraw and note deepest tooth having paint on it and next higher tooth that is not coated
  4. The wet film thickness lies between these two readings
  5. Clean gauge in any suitable solvent immediately after use
The drawing indicates that the tooth marked 3 mils has made contact with the wet paint and the tooth marked 4 mils has not. This indicates that the true wet film thickness of the material is between 3 and 4 mils thick.

In conclusion measuring the film thickness immediately after coating the surface is important to control the spreading rate and the final dry film thickness. Wet film thickness should be monitored frequently to maintain an efficient coating process and to ensure that the wet film measurement is in an acceptable range. A wet film thickness gauge is an inexpensive, easy to use device which covers a wide wet film thickness range from industrial maintenance applications to thin coil coatings. Wet film gauges can be used on virtually every substrate and have proved to aid in cost savings measures.


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