Many coating properties are markedly affected by the film thickness of the dry film such as adhesion, flexibility, and hardness. To be able to compare results obtained by different operators, it is essential to measure film thickness carefully.

Most protective and high performance coatings are applied to meet a requirement or a specification for the dry-film thickness of each coat, or for the complete system, or both. Coatings must be applied within certain minimum and maximum thickness tolerances in order that they can fulfill their intended function. In addition to potential performance deficiencies, it is uneconomical to apply more material than necessary when coating large areas such as floors and walls.

Surface roughness can affect the accuracy of this test method. A rough surface has a tendency to scatter the ultrasonic pulse and odd readings may occur occasionally.

This test method may not be applicable to measure organic coating thickness on all substrates. The instrument’ability to detect a distinct interface between the coating and the substrate may be impeded if the coating and the substrate are of similar composition of if the coating is non-homogeneous. Verify operation on a known thickness of the coating/substrate combination if these circumstances are thought to exist.

Multilayered coatings have many interfaces and the instrument will measure to the interface separating the two most acoustically different materials. Some instruments have the ability to detect and measure the individual layer thicknesses in a multi-layer system.

The use of this test method is not necessarily limited by the type of substrate material as nondestructive magnetic-type or eddy current means.

1.1 This test method covers the use of ultrasonic film thickness gages to measure accurately and nondestructively the dry film thickness of organic coatings applied over a substrate of dissimilar material. Measurements may be made on field structures, on commercially manufactured products, or on laboratory test specimens. These types of gages can accurately measure the dry film thickness of organic coatings on concrete, wood and wallboard substrates.

1.2 This test method is not applicable to coatings that will be readily deformable under load of the measuring instrument as the instrument probe is placed directly on the coating surface to take a reading.

1.3 The effective range of instruments using the principle of ultrasonics is limited by gage design. A thickness range of 0.3 to 600 mils (8 μm to 15 μmm) has been demonstrated.

1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

1.5 This standard does not purport to address the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.