This test method details the standard procedure for determining the porosity of white or near white mineral spirits insoluble paint film by staining to indicate the degree to which a subsequent coat will penetrate. This test method shall require the use of film applicators, reflectometer, vacuum drawdown plate, camelhair brush, plastic wash bottle, test panel, penetrating medium, and filter paper. The test paint is applied to a nonporous surface, air dried, then measured for reflectance. A special colored penetrating medium is applied, the excess removed in a specified manner, and reflectance measured again. The difference between the two readings indicates the degree of porosity; the smaller the difference, the lower the porosity of the film and the greater its ability to resist penetration.

1.1 This test method covers the determination of the porosity of a white or near white mineral spirits insoluble paint film to indicate the degree to which a subsequent coat will penetrate.

1.2 The texture of the film can affect cleanup that will influence the results of the test. A stain applied to a high-hiding paint will not lower the reflectance as much as the same stain applied to a low-hiding paint of equal porosity. These points must be considered in comparing different paints.

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

1.4 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.