ASTM D7378 : 10

1.1 This practice describes the thickness measurement of dry coating powders applied to a variety of rigid substrates. Use of some of these procedures may require repair of the coating powder. This practice is intended to supplement the manufacturers’ instructions for the operation of the gages and is not intended to replace them. It includes definitions of key terms, reference documents, the significance and use of the practice, and the advantages and limitations of the instruments.

1.2 Three procedures are provided for measuring dry coating powder thickness:

1.2.1 Procedure A—Using rigid metal notched (comb) gages.

1.2.2 Procedure B—Using magnetic or eddy current dry film thickness gages.

1.2.3 Procedure C—Using non-contact ultrasonic powder thickness instruments.

1.3 Coating powders generally diminish in thickness during the curing process. Some of these procedures therefore require a reduction factor be established to predict cured film thickness of powder coatings.

1.4 Procedure A and Procedure B

measure the thickness (height or depth) of the applied coating powders in the pre-cured, pre-gelled state. By comparing results to the measured cured powder thickness in the same location, a reduction factor can be determined and applied to future thickness measurements of the same coating powder.

1.5 Procedure C

results in a predicted thickness value of the cured state based on a calibration for typical coating powders. If the powder in question is not typical then an adjustment can be made to align gage readings with the actual cured values as determined by other measurement methods.

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

1.7 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 and health practices and determine the applicability of regulatory limitations prior to use.