Wood preservation
Wood preservation refers to any method or process, or even technique, used to protect wood and extend its service life.
Most wood species are susceptible to both biological and non-biological factors that cause decay and/or deterioration. Only a limited number of wood species possess natural durability, and even those may not be suitable for all environments. In general, wood benefits from appropriate preservation measures.
In addition to structural design considerations, a variety of chemical preservatives and treatment processes — commonly known as timber treatment, lumber treatment, pressure treatment or modification treatment — are used to enhance the durability of wood and wood-based products, including engineered wood. These treatments may involve physical, chemical, thermal, and/or biological methodology aimed at protecting wood from degradation. They increase its resistance to biological agents such as fungi, termites, and insects, as well as non-biotic factors such as ultraviolet radiation, moisture and wet-dry cycling, temperature extremes, mechanical wear, exposure to chemicals, and fire or heat. Effective preservation treatments significantly improve the durability, structural integrity, and overall performance of wood in service.
History
As proposed by Richardson, treatment of wood has been practiced for almost as long as the use of wood itself. There are records of wood preservation reaching back to ancient Greece during Alexander the Great's rule, where bridge wood was soaked in olive oil. The Romans protected their ship hulls by brushing the wood with tar. During the Industrial Revolution, wood preservation became a cornerstone of the wood processing industry. Inventors and scientists such as Bethell, Boucherie, Burnett and Kyan made historic developments in wood preservation, with preservative solutions and processes. Commercial pressure treatment began in the latter half of the 19th century with the protection of railroad cross-ties using creosote. Treated wood was used primarily for industrial, agricultural, and utility applications, where it is still used, until its use grew considerably in the 1970s, as homeowners began building decks and backyard projects. Innovation in treated timber products continues to this day, with consumers becoming more interested in less toxic materials.Hazards
Wood that has been industrially pressure-treated with approved preservative products poses a limited risk to the public and should be disposed of properly. On December 31, 2003, the U.S. wood treatment industry stopped treating residential lumber with arsenic and chromium. This was a voluntary agreement with the United States Environmental Protection Agency. [|CCA] was replaced by copper-based pesticides, with exceptions for certain industrial uses. CCA may still be used for outdoor products like utility trailer beds and non-residential construction like piers, docks, and agricultural buildings. Industrial wood preservation chemicals are generally not available directly to the public and may require special approval to import or purchase, depending on the product and the jurisdiction where being used. In most countries, industrial wood preservation operationsl are notifiable industrial activities that require licensing from relevant regulatory authorities such as EPA or equivalent. Reporting and licensing conditions vary widely, depending on the particular chemicals used and the country of use.Although pesticides are used to treat lumber, preserving lumber protects natural resources by enabling wood products to last longer. Previous poor practices in industry have left legacies of contaminated ground and water around wood treatment sites in some cases. However, under currently approved industry practices and regulatory controls, such as implemented in Europe, North America, Australia, New Zealand, Japan and elsewhere, environmental impact of these operations should be minimal.
Wood treated with modern preservatives is generally safe to handle, given appropriate handling precautions and personal protection measures. However, treated wood may present certain hazards in some circumstances, such as during combustion or where loose wood dust particles or other fine toxic residues are generated, or where treated wood comes into direct contact with food and agriculture.
Preservatives containing copper in the form of microscopic particles have recently been introduced to the market, usually with "micronized" or "micro" trade names and designations such as MCQ or MCA. The manufacturers represent that these products are safe and EPA has registered these products.
The American Wood Protection Association recommends that all treated wood be accompanied by a Consumer Information Sheet, to communicate safe handling and disposal instructions, as well as potential health and environmental hazards of treated wood. Many producers have opted to provide Material Safety Data Sheets instead. Although the practice of distributing MSDS instead of CIS is widespread, there is an ongoing debate regarding the practice and how to best communicate potential hazards and hazard mitigation to the end-user. Neither MSDS nor the newly adopted International Safety Data Sheets are required for treated lumber under current U.S. Federal law.
Chemical
In general, the chemical preservatives can be classified into three broad categories:- water-borne preservatives
- oil-borne preservatives
- light organic solvent preservatives
Micronized copper
Particulate copper preservative technology has been introduced in the US and Europe. In these systems, copper is ground into micro sized particles and suspended in water rather than dissolved, as is the case with other copper products such as ACQ and copper azole. There are two particulate copper systems in production. One system uses a quat biocide system and is a derivative of ACQ. The other uses an azole biocide derived from copper azole.Two particulate copper systems, one marketed as MicroPro and the other as Wolmanized using μCA-C formulation, have achieved Environmentally Preferable Product certification. The EPP certification was issued by Scientific Certifications Systems and is based on a comparative life-cycle impact assessments with an industry standard.
The copper particle size used in the "micronized" copper beads ranges from 1 to 700 nm with an average under 300 nm. Larger particles of copper do not adequately penetrate the wood cell walls. These micronized preservatives use nano particles of copper oxide or copper carbonate, for which there are alleged safety concerns. An environmental group petitioned EPA in 2011 to revoke the registration of the micronized copper products, citing safety issues.
Alkaline copper quaternary
is a preservative made of copper, a fungicide, and a quaternary ammonium compound like didecyl dimethyl ammonium chloride, an insecticide which also augments the fungicidal treatment. ACQ has come into wide use in the US, Europe, Japan and Australia following restrictions on CCA. Its use is governed by national and international standards, which determine the volume of preservative uptake required for a specific timber end use.Since it contains high levels of copper, ACQ-treated timber is five times more corrosive to common steel. It is necessary to use fasteners meeting or exceeding requirements for ASTM A 153 Class D, such as ceramic-coated, as mere galvanized and even common grades of stainless steel corrode. The U.S. began mandating the use of non-arsenic containing wood preservatives for virtually all residential use timber in 2004.
The American Wood Protection Association standards for ACQ require a retention of for above ground use and for ground contact.
Chemical Specialties, Inc received U.S. Environmental Protection Agency's Presidential Green Chemistry Challenge Award in 2002 for commercial introduction of ACQ. Its widespread use has eliminated major quantities of arsenic and chromium previously contained in CCA.
Copper azole
Copper azole preservative is a major copper based wood preservative that has come into wide use in Canada, the US, Europe, Japan and Australia following restrictions on CCA. Its use is governed by national and international standards, which determine the volume of preservative uptake required for a specific timber end use.Copper azole is similar to ACQ with the difference being that the dissolved copper preservative is augmented by an azole co-biocide like organic triazoles such as tebuconazole or propiconazole, which are also used to protect food crops, instead of the quat biocide used in ACQ. The azole co-biocide yields a copper azole product that is effective at lower retentions than required for equivalent ACQ performance. The general appearance of wood treated with copper azole preservative is similar to CCA with a green colouration.
Copper azole treated wood is marketed widely under the Preserve CA and Wolmanized brands in North America, and the Tanalith brand across Europe and other international markets.
The AWPA standard retention for CA-B is for above ground applications and for ground contact applications. Type C copper azole, denoted as CA-C, has been introduced under the Wolmanized and Preserve brands. The AWPA standard retention for CA-C is for above ground applications and for ground contact applications.
Copper naphthenate
, invented in Denmark in 1911, has been used effectively for many applications including: fencepost, canvas, nets, greenhouses, utility poles, railroad ties, beehives, and wooden structures in ground contact. Copper naphthenate is registered with the EPA as a non-restricted use pesticide, so there is no federal applicators licensing requirements for its use as a wood preservative. Copper Naphthenate can be applied by brush, dip, or pressure treatment.The University of Hawaii has found that copper naphthenate in wood at loadings of is resistant to Formosan termite attack. On February 19, 1981, the Federal Register outlined the EPA's position regarding the health risks associated with various wood preservatives. As a result, the National Park Service recommended the use of copper naphthenate in its facilities as an approved substitute for pentachlorophenol, creosote, and inorganic arsenicals. A 50-year study presented to AWPA in 2005 by Mike Freeman and Douglas Crawford says, "This study reassessed the condition of the treated wood posts in southern Mississippi, and statistically calculated the new expected post life span. It was determined that commercial wood preservatives, like pentachlorophenol in oil, creosote, and copper naphthenate in oil, provided excellent protection for posts, with life spans now calculated to exceed 60 years. Surprisingly, creosote and penta treated posts at 75% of the recommended AWPA retention, and copper naphthenate at 50% of the required AWPA retention, gave excellent performance in this AWPA Hazard Zone 5 site. Untreated southern pine posts lasted 2 years in this test site."
The AWPA M4 Standard for the care of preservative-treated wood products, reads, "The appropriateness of the preservation system for field treatment shall be determined by the type of preservative originally used to protect the product and the availability of a field treatment preservative. Because many preservative products are not packaged and labeled for use by the general public, a system different from the original treatment may need to be utilized for field treatment. Users shall carefully read and follow the instructions and precautions listed on the product label when using these materials. Copper naphthenate preservatives containing a minimum of 2.0% copper metal are recommended for material originally treated with copper naphthenate, pentachlorophenol, creosote, creosote solution or waterborne preservatives." The M4 Standard has been adopted by the International Code Council's 2015 International Building Code section 2303.1.9 Preservative-treated Wood, and 2015 International Residential Code R317.1.1 Field Treatment. The American Association of State Highway and Transportation Officials AASHTO has also adopted the AWPA M4 Standard.
A waterborne copper naphthenate is sold to consumers under the tradename QNAP 5W. Oilborne copper naphthenates with 1% copper as metal solutions are sold to consumers under the tradenames Copper Green, and Wolmanized Copper Coat, a 2% copper as metal solution is sold under the tradename Tenino.