ASTM D3456

ASTM D3456 – Standard Practice for Determining by Exterior Exposure Tests the Susceptibility of Paint Films to Microbiological Attack

Description:

Significance and Use

3.1 The growth of fungi and algae in and on the surface of paint films represents a major cause of discoloration or disfigurement of painted surfaces.

3.2 Simple observation of a coated object subjected to exterior exposure is considered a practical and reliable method for determining the degree that microorganisms discolor the coating. However, this applies to a specific coated object exposed under a given set of conditions.

3.3 It should be recognized that there are critical factors that influence the amount of microbial growth that may occur on the same coated object when exposed to other conditions. These factors include the geographic location, local atmospheric conditions such as the dust and pollen content of the air, angle of exposure, degree to which the coating is subjected to weathering, effects of moisture and sunlight, the substrates on which the coating is applied, and the coatings in the paint system under test. The latter factor includes the stability of the coating while packaged in the container, as well as the composition of the coatings included in the total system and the thickness of each coating applied. Thus, while microorganisms occur on the surface of the last film applied, the degree of microbiological growth that will occur is also influenced by the composition of the undercoats. All the above factors should be considered in the selection of a coating resistant to discoloration by microorganisms.

Scope

1.1 This practice provides guidelines for determining the susceptibility of paint films to microbiological attack on exterior exposure. While it is recognized that various organisms may occur on an exposed coating, the specific types of organisms are mainly of academic interest. The degree to which microbiological discoloration occurs is the primary concern.

1.2 This practice covers the preparation of coatings for testing, their application on substrates, and the arrangement of the coated panels on exterior test racks to determine the degree of microbiological attack that may occur on the surface of the coatings over a period of time.

1.3 This practice is intended to provide guidelines for, and a discussion of, the various factors critical in selection of exterior coatings resistant to discoloration or disfigurement by algae and fungi.

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