The test method details a standard procedure for determining the porosity of white or near-white mineral oil insoluble paint films by staining to indicate the degree of penetration of subsequent coatings. This test method shall require the use of a film applicator, reflectometer, vacuum extraction plate, camel hair brush, plastic washing bottle, test plate, penetration medium and filter paper. The test paint was applied to a non-porous surface, air dried, and then the reflectivity was measured. A special colored penetrating medium was applied to remove the excess in the specified manner and the reflectivity was measured again. The difference between two readings indicates porosity; The smaller the difference is, the lower the porosity of the film is and the stronger the resistance to penetration is.

ASTM D3258-2019 Porosity of Paint Film Abstract

Scope of
1.1 The test method covers the determination of the porosity of white or near-white mineral oil insoluble paint films to indicate the degree of penetration of subsequent coatings.

1.2 The texture of the film will affect the cleaning and thus the test results. A stain applied to a high shading paint does not reduce the reflectivity as much as the same stain applied to a low shading paint with equal porosity. These points need to be considered when comparing different paints.

1.3 Values expressed in SI units shall be regarded as standards. The values given in parentheses are for reference only.

ASTM D3258-2019 Porosity of Paint Film Abstract

1.4 This standard is not intended to address all safety issues, 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 to determine the applicability of regulatory restrictions prior to use.

1.5 This international Standard has been developed in accordance with the internationally recognized standardization principles established in the Decision on Principles for the Development of International Standards, Guidelines and Recommendations issued by the Committee on Technical Barriers to Trade of the World Trade Organization.