The test method in ASTM D3258 details a standard procedure for determining the porosity of white or near-white mineral oil insoluble paint films by staining to indicate the degree to which subsequent coatings will permeate.
abstraction

This 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 to which subsequent coatings will permeate. The test method shall require the use of film coater, reflectometer, vacuum scraping plate, camel hair brush, plastic wash bottle, test plate, permeating medium and filter paper. The test paint is applied to a non-porous surface, air dried, and then the reflectivity is measured. A special color permeating medium is applied, excess medium is removed in a specified manner, and reflectivity is measured again. The difference between the two readings indicates porosity; The smaller the difference, the lower the porosity of the film and the stronger its permeability resistance.

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ASTM D3258-19 Standard Test Method for Determination of Porosity of White or Near-White Paint Films by Staining

Step 1: Scope

1.1 The test method includes the determination of the porosity of a white or near-white mineral oil insoluble paint film to indicate the degree of subsequent coating penetration.

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

1.3 Values expressed in SI units shall be considered standard. The values given in parentheses are for reference only.

1.4 This standard is not intended to address all safety concerns, if any, associated with its use. It is the responsibility of users of this standard to establish appropriate safety, health and environmental practices and to determine the applicability of regulatory restrictions prior to use.

1.5 The international standard is based on 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 (TBT) of the World Trade Organization.