Significance and Use 5.1 Many coating properties are markedly affected by the film thickness of the dry film such as adhesion, flexibility, wear, durability, chemical resistance, and hardness. To be able to compare results obtained by different operators, it is essential to measure film thickness carefully. 5.2 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. 5.3 Low readings may occur occasionally on coatings with rough surfaces. The instrument may allow a user adjustment to prevent this. 5.4 This test method may not be applicable to measure organic coating thickness on all substrates. The instrument’s 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, density or attenuation or if the coating is non-homogeneous. Verify operation on a known thickness of the coating/substrate combination if these circumstances are thought to exist. 5.5 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. 5.6 The use of this test method is not necessarily limited by the type of substrate material.Scope 1.1 This test method describes 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 a variety of substrates such as concrete, wood, wallboard, plastic, fiber composites and metal. 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 8 μm to 7.60 mm (0.3 to 300 mils) has been demonstrated. 1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
