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Remarkable increases in the performance of complex systems can be achieved by a collective approach to optimizing individual factors that influence performance. This approach, termed the aggregation of marginal gains, is tested here as a means of improving the performance of exterior clear-coatings. We focused on five factors that influence clear-coating performance: dimensional stability of wood; photostability of the wood surface; moisture ingress via end-grain; coating flexibility and photostability; and finally coating thickness. We performed preliminary research to select effective wood pre-treatments and durable clear-coatings, and then tested coating systems with good solutions to each of the aforementioned issues (factors). Red oak and radiata pine panels were modified with PF-resin, end-sealed, and thick acrylic, alkyd or spar varnishes were applied to the panels. Panels were exposed to the weather and the level of coating defects was assessed every year over a 4-year period. All of the coatings are performing well on PF-modified pine after 4 years' outdoor exposure. In contrast, coatings failed after 2 years on unmodified pine and they are failing on PF-modified oak. We conclude that our approach shows promise. Future research will build on the current work by developing solutions to additional factors that influence clear-coating performance.

We examine the performance of clear coatings on wood treated to improve its photostability. The treatments tested were: benzoyl chloride; chromic acid; modified PF resins; vinyl benzoate; and primers containing different photostabilisers. Treated panels were finished with clear coatings containing different types/levels of photostabilisers and exposed outdoors in Australia for 2 years. The coatings performed better on treated than untreated panels, except for coatings on panels treated with a primer containing cerium oxide nanoparticles. Clear coatings performed best on wood treated with chromic acid, vinyl benzoate or PF resin containing a hindered amine light stabiliser. However, the performance of the coatings was also strongly influenced by coating type. We conclude that the performance of clear coatings can be increased if they are applied to photostable wood substrates. However, coating performance is also dependent on coating flexibility, its propensity to form surface defects, and the level/types of photostabiliser in the coatings.

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