Challenges in weathering testing

What are the challenges in testing and measuring paints at the moment?

Andy Francis: A major challenge in weathering and corrosion testing is the difficulty in developing test protocols that yield results that are well-correlated to outdoor exposures, and the time required to actually conduct benchmark outdoor testing.

Even small changes in formulation can result in significant changes in outdoor durability and manufacturers are not going to share their chemistries nor their test results. Although test standards for weathering and corrosion of paints are evolving, it is necessary still to perform long-term, outdoor exposures to take the true measure of their resistance to sunlight, heat, water, salt, and other natural factors.

Which advancements in weathering testing do you consider most promising?

Francis: Modern xenon, UV fluorescent, and metal halide test technologies allow more precise and realistic testing than ever before. It’s positive to see increasing industry recognition that it’s critical to simulate multiple failure modes and weathering stresses to get good correlative testing for coatings.

We have been stressing water delivery in accelerated weathering testing in our educational presentations – how one can speed up the process of water existing on surfaces for long periods of time each day, as well as how accelerated testers can reproduce the effects of dew, as well as the erosive character of rain. I think work on this will do a lot for weathering testing of coatings.

How much is the sector influenced by standardisation?

Francis: The paint and coatings weathering and corrosion testing sector, including fluorescent UV, xenon arc, and salt corrosion tests, is guided by standards. Most in the industry use long-standing international test standards from ISO, ASTM and major original equipment manufacturers (OEMs). The majority of testing is quality control-type testing to standards like ASTM G154 and G155; ISO 4892-2 and -3; and ASTM B117, which may not correlate well to outdoor exposure.

Test standards like ASTM D7869, developed specifically for transportation coatings, offer improved realism and correlation to outdoor results, and have gained some acceptance in the sector.