New Wood Preservative Treatments

Pressure-Treated Wood: The Next Generation (Journal of Light Construction, April 2009) reports on new chemical preservative treatments for wood that promise to be less corrosive than the current generation of preservatives, but that leave unanswered questions about long-term performance.

Second-Generation Preservatives
Until recently, the two most popular chemicals used to treat wood for protection from decay and insect attack were CA (copper azole) and ACQ (ammoniacal copper quaternary or alkaline copper quarternay). Both of these chemicals rely on high concentrations of dissolved copper for their resistance to attacks by fungi and and insects. But these high copper concentrations, can also cause rapid corrosion of metal fasteners and framing hardware with which the treated wood comes in contact.

For example, the article refers to tests of ACQ treated lumber with plain or galvanized steel which have shown corrosion rates 5 to 15 times that of CCA, the preservative chemical that ACQ and CA replaced but that was removed from the market in 2004 because of concerns for health hazards due to its arsenic content.

Third-Generation and Beyond Preservatives
Unlike CA and ACQ, in which the copper is in a dissolved (ionized) state and relatively free to migrate, a new family of chemicals rely on finely ground particles of copper in suspension that results in less free copper ions and less corrosion of metals. Chemical formulas, which vary with preservative manufacturer,  include uCA-C (dispersed copper azole), MCA (micronized copper azole), and MCQ (micronized copper quaternary). Manufacturers of these copper-suspension treatment chemicals claim reduced corrosion rates in comparison to copper-solution treatments. 

Preservatives which rely on boron for decay prevention are another alternative. These chemicals have no corrosive affect and no know health risks. But most are also highly water soluble, making them suitable only for applications protected from the weather such as interior wood framing for structures in areas of high termite risk. One treatment manufacturer produces a borate treatment chemically bound to the wood such that it can be used for exterior, non-ground contact applications.

The newest family of preservatives entering the market are based on organic insecticides and fungicides with no copper or other metals. These so-called "carbon-based" treatments promise much lower corrosivity than copper-based treatments. Currently available products are suitable for above-ground use only and include the chemicals EL2 (DCOI-Imidicloprid) and PTI (Propiconazole-Tebuconazole-Imidicloprid).

Performance
While new treatment chemicals must pass laboratory testing to demonstrate their effectiveness, their true long-term performance in real-world conditions won't be certain for decades. In the mean time, designers and builders must base their product selections on the results of standard testing and manufacturer certifications.

More Info
http://www.archchemicals.com/Fed/WOLW/
www.treatedwood.com
www.osmosewood.com
www.frtw.com
www.phibrowood.com