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Deck Stains Seal In Contaminants

A semitransparent penetrating stain might prevent the metal and other inorganic preservatives from escaping from treated wood

by Sarah Everts
July 26, 2010 | A version of this story appeared in Volume 88, Issue 30

When it was discovered that the chromated copper arsenate used to protect household decks from decay leached arsenic onto the wood surfaces and into the environment, a public outcry pushed industry to find alternatives, such as copper amine-based preservatives. But it is now thought that copper leaching from this wood might also hurt aquatic animals. Consequently, Mojgan Nejad and Paul Cooper of the University of Toronto decided to investigate whether adding a semitransparent penetrating stain might prevent the metal and other inorganic preservatives from escaping. The researchers applied 14 commercially available stains to deck wood and found that on average each coating prevented 60% of all inorganic preservative components from trickling out of the wood (Environ. Sci. Technol., DOI: 10.1021/es101138v). Although most of the coatings seemed to physically degrade after about a year, the protective characteristics remained throughout Nejad and Cooper’s three-year study; the wood likely retained the preservative components of the stains, or the stain somehow fixed the copper within the wood. The researchers also found that stains with high liquid viscosities and low glass transition temperatures did a better job of blocking leaching.


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