What instrument is primarily utilized for measuring the thickness of a coating during its application?

The wet-mil gauge is specifically designed to measure the thickness of a wet coating as it is being applied. This tool allows the user to determine the coating thickness in mils (thousandths of an inch) while the material is still in its liquid state. This is crucial because achieving the correct film thickness is essential for the performance and longevity of coatings, especially in roofing applications.

While a caliper is used for various measurements of depth and thickness, it is not specialized for wet coatings. A micrometer, although precise, is more suited for measuring solid materials and is not typically used during the application of coatings. A thickness gauge can refer to a variety of tools used for measuring material thickness, but it does not provide the specific functionality needed for wet coatings like the wet-mil gauge does.