UBC Theses and Dissertations

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UBC Theses and Dissertations

Envelope protection of preservative-treated pine decking with modified low molecular weight phenol formaldehyde resin Chan, Wing Fung George


Preservative-treated pine is commonly used for outdoor decking in Canada and the United States, but its attractive appearance is lost when it is exposed to the weather. Wood can be protected from ‘weathering’ using low molecular weight phenol formaldehyde (LMW PF) resin. In this thesis, I combine preservative treatments and modification of wood with PF resin to try to develop wood decking with superior resistance to weathering. My hypothesis is that shallow ‘envelope’ modification of treated wood with LMW PF resin containing photostabilizers and wax additives will protect the appearance of preservative-treated pine decking exposed to natural weathering. I first screened different additives for their ability to protect wood from the adverse effects of weathering. The best additives were selected for further testing. Preservative-treated Scots and southern pine boards were modified by dipping or vacuum impregnation with modified PF resins, and modified and treated boards were exposed to the weather. Envelope modification restricted checking of untreated pine boards weathered for two years. Degradation of modified boards was shallow and easily cleaned off. Underneath the weathered grey layer, the colour of PF-modified wood was retained. Envelope modification with different PF resin formulations also protected treated boards weathered for six months. Ferric chloride was a more effective additive than a lignin stabilizer for most substrates (treated or untreated). The dark colour of PF/ferric-modified wood masked mould. The different PF resins I tested improved the performance of treated wood to varying degrees, but their effectiveness depended on the substrate they were applied to. I conclude that: (1) envelope modification with PF and modified PF resins is able to protect treated decking from the adverse effects of weathering; (2) vacuum impregnation with PF resin is a better method than dipping at creating an effective weather-resistant envelope at the surface of treated wood decking; (3) PF and additives need to be tailored to suit different preservative-treated woods; (4) PF modification shows promise as a finishing process to enhance weathering resistance of treated wood.

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