Overview of the treated wood quality control program in the United States with the recent challenges and advances
In the past two decades, there have been significant and rapid changes in wood protection technologies for residential applications which have moved away from long established heavy duty metal oxide based products such as chromated copper arsenate (CCA). The successor generation of wood protection systems usually contain copper as the primary biocide, in combination with carbon-based co-biocides such as quaternary ammonium compounds (Quat), and/or triazoles (Tebuconazole and/or Propiconazole). The most recent developments have given rise to even more complicated combinations including multiple carbon-based biocides formulated in the form of emulsions or dispersions with or without water repellents or polymers aiming to minimize the use of heavy metals as well as provide improvement in wood dimensional stability and surface weathering performance. Also, long developed non-biocidal wood modification treatments, such as acetylation, thermal modification, furfurylation and hydrocarbon wax/oil treated wood have finally gained more commercial traction in the market place, especially in Europe. These new developments have challenged the industry to develop and use appropriate methods in order to meet the quality control (QC) standards and requirements in respect to concentration of treatment solutions, as well as chemical retention and penetration in treated wood.
In the US, the QC system for treated wood product includes three key elements: treating plant internal QC for treating solution, treated wood, and treatment process; QC assistance and monitoring by the chemical/technological suppliers for their customers, and QC inspection by third-party inspection agencies. The enforcement of the QC standards through this comprehensive system is essential to ensure the performance of the treated wood products, the validity of product warranty program, and ultimately for the protection of consumers and the public.
This paper overviews the US’s current QC standards and procedures used by treating plants, suppliers and independent inspection agencies. The chemistry challenges with the recent developments of multi-component systems and complex wood protection technologies, and their impacts on quality control methods are also discussed. Case studies have been used to illustrate how some of these challenges can and have been successfully addressed.
Keywords: wood protection, wood preservatives, wood modification, CCA, Alkaline Copper Quat, ACQ, Copper Azole, CA, Ecolife, EL2, quality Control, QC, preservative solution concentration, chemical retention and penetration, AWPA Standards