How to Measure Dry Film Thickness

A dry film is the coating on a surface which has cured. The coating is typically a paint, a varnish or a cured powder. But it can be any substance applied to a substrate. Throughout this section, we will consider the coating to be paint which is used for cosmetic or protective purposes.

A dry film thickness (DFT) gauge, often referred to as a coating thickness gauge, can be used to measure the thickness of any of these coatings when dry. Measuring dry film thickness is important when assessing cost, quality and service life of the coating.

A coating which is too thick means that excessive material is being used, increasing costs. Excessive paint can also lead to uncured paint under the surface making the coating fragile and likely to damage prematurely. A coating which is applied too thinly can result in the surface not being protected sufficiently causing rust rash or rust spots and premature failure of the overall system.

In the field of protective coatings, coating standards and paint specifications stipulate not only a nominal dry film thickness (DFT) for each coating applied in a system but also a minimum DFT and a maximum DFT.

The measurement of dry film coating thickness (DFT) can be broken down into two distinct categories; destructive and non-destructive.