Accelerated weathering testing is used during sealant development mainly to establish a relative ranking of the formulas under examination (as illustrated in the previous chapter).
In some cases, however, the actual performance in “hours of durability” will be needed: In order to ensure the necessary durability and weathering performance of a sealant, customers often require sealants to pass a certain time in an accelerated weathering test. For example, in the case of carbon arc accelerated weathering, often 1500-2000 h of exposure time is required for construction sealants. In more demanding cases, such as for industrial applications, 5000, 10 000, or more hours of carbon arc weathering may be requested.
Accelerated weathering requirements can be tested under defined conditions and the results are reproducible for a given piece of equipment. However, not all customers require accelerated weathering tests merely to ascertain the actual durability of a sealant; weathering data can also serve as basis for warranties for minimum service life. In these cases, the task of finding a correlation between the accelerated weathering data and the actual service life lies with the sealant producer.
Such service life requirements can range anywhere from 5 to 30 years (or more), however, 10 to 20 years are most frequently encountered. However, the actual outdoor conditions are often poorly defined and conditions can change during the service life of a sealant. Therefore, the actual service life is difficult to assess and predictions have a large degree of uncertainty [1,10].