The clear film durability of wood is generally very short because of photo degradation of wood surfaces caused by UV through to the film. Pre-treatment of wood surfaces for protecting against photodegradation is very important for clear finishing system. In this study, some pre-treatments, ie; polyethylene glycol (PEG) and UVA grafting (2-hydroxy-4(2,3-epoxypropoxy) benzophenone (HEPBP)), were applied to wood surfaces and evaluated the clear finishing durability at outdoors. PEG treatment showed good clear film durability at mild climatic places, however, less durable results were observed at warm and high humid or heavy snow area in Japan. UVA grafting to wood surfaces greatly improved clear film durability as well as chromium trioxide treatment. Mixtures of UVA, HALS and anti mould chemicals system showed to prevent for growing mould on wood surfaces finished with clear or light color exterior stain system.

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