Standard Practice for Conducting Exterior Exposure Tests of Paints and Coatings on Metal Substrates
The procedures described in this practice are intended to aid in evaluating the performance of coatings on various metal panels including either new or previously rusted steel.
The relative durability of paints in outdoor exposures can be very different depending on the location of the exposure because of differences in solar radiation, time of wetness, temperature, pollutants, and other factors. Therefore, it cannot be assumed that results from one exposure in a single location will be useful for determining relative durability in a different location. Exposures in several locations with different climates which represent a broad range of anticipated service conditions are recommended.
4.2.1 Because of year-to-year climatological variations, results from a single exposure test cannot be used to predict the absolute rate at which a material degrades. Several years of repeat exposures are needed to get an “average” test result for a given location.
4.2.2 Solar radiation varies considerably as function of time of year. This can cause large differences in the apparent rate of degradation in many polymers. Comparing results for materials exposed for short periods (less than one year) is not recommended unless materials are exposed at the same time in the same location.
The Significance and Use in Practice G 7 addresses many variables to be considered in exterior exposure tests. Guide G 141 provides more information on variability in weathering testing.
1.1 This practice covers procedures to be followed for direct exposure of exterior paints and coatings to the environment when applied to metal surfaces. When originators of a weathering test have the actual exposure conducted by a separate agency, the specific conditions for the exposure of test and control specimens should be clearly defined and mutually agreed upon between all parties.
1.2 Experience indicates that the metal used as a test substrate has a significant effect upon weathering results. The purpose of this practice is to define specific steel and other metal surfaces to be used for testing in order to minimize this source of variability.
1.3 The values stated in SI units are to be regarded as the standard.
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.
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