As with any accelerated test, the increase in rate of weathering compared to in-service exposure is material dependent. Results from exposures conducted to this practice may provide good rank correlation to results from actual use conditions for one type of material or product. It should not be assumed that this will be true for other materials or products. It is always best to verify the ability of an accelerated exposure test to properly rank the durability of materials with actual use conditions. Guide G141 provides information about using rank correlation.

Variation in results may be expected when operating conditions are varied within the accepted limits of this practice. Therefore, no reference shall be made to results from the use of this practice unless accompanied by a report detailing the specific operating conditions in conformance with Report Section 8.

The durability of materials in outdoor use can be very different depending on the location of the exposure because of differences in solar radiation, moisture, heat, pollutants, and other factors. Therefore, it cannot be assumed that results from exposure in a single location will be useful for determining durability ranking of materials in a different location.

It is strongly recommended that at least one control material be exposed with each test. The control material should be of similar composition and construction and be chosen so that its failure modes are the same as that of the material being tested. It is preferable to use two control materials, one with relatively good durability, and one with relatively poor durability. If control materials are included as part of the test, they shall be used for the purpose of comparing the performance of the test materials relative to the controls.

1.1 This practice covers the basic principles and operating procedures for using outdoor glass-covered exposure apparatus with air circulation. This practice is limited to the procedures for obtaining, measuring and controlling conditions of exposure. A number of exposure procedures are listed in Appendix X1; however, this practice does not specify the exposure conditions best suited for the material to be tested.

1.2 For direct weathering exposures, refer to Practice G7. For exposures behind glass without air circulation, refer to Practice G24.

1.3 Test specimens are exposed to solar radiation filtered through glass under partially controlled environmental test conditions. Different glass types and operating parameters are described.

1.4 Specimen preparation and evaluation of the results are covered in ASTM methods or specifications for specific materials. More specific information for determining the change in properties after exposure and reporting these results is described in Practices D5870, D2244 and Test Method D523.

1.5 The values stated in SI units are to be regarded as standard.

1.6 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.