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Preservative treated wood: health & environmental concerns when working with or using treated lumber: this article discusses deck framing lumber treatment methods, the use of pressure treated lumber, Health Concerns for Chromated-Copper Arsenate (CCA) Pressure Treated Lumber, Advice for Existing Structures Built Using Chromated-copper Arsenate (CCA) Treated Lumber, Health Precautions for Alkaline Copper Quat (ACQ)-Treated Lumber, and Retention Ratings: Treatment Levels & Durability of Alkaline Copper Quat (ACQ)-Treated Lumber.
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Pressure-Treated (PT) Lumber
The vast majority of residential decks were framed with lumber treated with chromated-copper arsenate (CCA) until 2004, when CCA was phased out and replaced primarily by alkaline copper quat (ACQ) and copper azole. The treated lumber is typically Southern yellow pine in the eastern United States and hem-fir in the West. The more expensive and stronger Douglas fir is also used in the West, but it is more likely treated with the waterborne treatment ammoniacal copper zinc arsenate (ACZA).
Incising Lumber for Treatment Penetration
Both Douglas fir and hem-fir are typically “incised” with surface cuts for better penetration of the treatment chemical. Even with incising, however, full chemical penetration is rarely achieved with these species, so the center of that wood remains vulnerable to rot, particularly in 4x and larger material.
With these species, effective field treatment of holes and cuts with a liquid preservative is essential.
Health Concerns for Chromated-Copper Arsenate (CCA) Pressure Treated Lumber
Despite CCA’s track record as an effective, economical wood preservative, its safety has long been questioned by health and environmental advocates. Their primary focus has been CCA’s heavy concentration of arsenic, a known carcinogen.
Although most experts agree that leaching of arsenic from CCA lumber is minimal and poses negligible health risks to end users, the industry acknowledges that CCA does pose risks to workers who handle the wet wood or burn scraps, and significant pollution around treating plants has been well documented.
Also see Wood Construction Products MSDS.
Phase Out of Chromated-copper Arsenate (CCA) Treated Lumber
In response to these concerns, manufacturers began a voluntary phase out in 2003 of all CCA treated lumber for noncommercial applications. Starting January 1, 2004, the Environmental Protection Agency (EPA) banned the manufacture of CCA-treated lumber intended to be used in residential settings, including retaining walls, decks, fencing, and playground equipment.
Pressure-treated shakes and shingles were exempted. CCA treatment will also still be available for plywood and heavy timbers used in commercial, industrial, and marine applications. Existing stocks of CCA-treated lumber were mostly depleted by the end of 2004.
Advice for Existing Structures Built Using Chromated-copper Arsenate (CCA) Treated Lumber
The EPA has issued no warnings regarding existing installations of CCA-treated lumber. However, for homeowners who are concerned about potential exposure to chemicals leaching out of the wood, researchers at the USDA Forest Products Laboratory (FPL) recommend periodically treating the pressure-treated lumber with a water-repellant or a semitransparent penetrating stain. Film-forming finishes, such as paints, are not recommended.
New Wood Preservative & Deck Lumber Treatment Chemicals: Alkaline Copper Quat (ACQ) and Copper Azole
Copper azole Type B (CA-B) has largely replaced Type A (CBC-A) in the United States and Canada.
Both ACQ and copper azole perform as well as CCA and are free of any EPA-listed hazardous compounds.
As with CCA-treated wood, premium treated lumber is available with a factory-applied water repellant.
With significantly higher copper content than CCA lumber, the new materials are 10 to 15% more expensive.
Of greater concern is the fact that the higher concentration of copper makes the lumber more corrosive to certain metals and metal coatings (see “Increased Corrosion Potential,” next page).
Health Precautions for Alkaline Copper Quat (ACQ)-Treated Lumber
Despite the lack of chromium, arsenic, or other hazardous chemicals, wood treated with alkaline copper quat (ACQ) and copper azole carry essentially the same handling instructions as CCA-treated materials. Workers handling ACQ and copper azole are still advised by the EPA to wear gloves or wash hands after contact, wear a dust mask when cutting, and not to burn the scraps. Like CCA-treated wood, it is not recommended for direct contact with food or drinking water.
Retention Ratings: Treatment Levels & Durability of Alkaline Copper Quat (ACQ)-Treated Lumber
While most CCA lumber was rated for ground contact, manufacturers are holding down costs with ACQ and copper azole by limiting treatment levels to the expected application of the lumber. For example, deck boards, 2x6s, and 4x4s at the lumberyard will typically have three different treatment levels (Table 4-2 below).
In most cases, lumber will be stamped or tagged with a designation such as “decking,” “above ground,” “ground contact,” or “PWF” (permanent wood foundation). Make sure the material purchased is rated for the intended application or one level higher.
Borate Treatment for Lumber & Deck Framing
Wood preservatives based on borate compounds have been used for decades abroad and are slowly becoming available in the United States. Borates are noncorrosive to metals and harmless to pets and humans, but they are very effective against insects and decay. Borate’s main limitation is its tendency to leach out of wood that is buried in soil or exposed to regular wetting, making it unsuitable for decks or other exterior applications.
New techniques to better fix the compounds into wood are under development, however, and may soon offer a viable alternative to copper-based treatments.
Increased Corrosion Potential for ACQ and Copper Azole-Treated Lumber
Because of their higher concentrations of copper, ACQ and copper azole are significantly more corrosive to aluminum, steel, and galvanized coatings than CCA (see “Galvanic Corrosion,” page 83). Preliminary tests have also shown that formulations with ammonia-based carriers (used for better penetration in heartwood species such as Douglas fir) are more corrosive than those with an amine or hybrid bases.
Many factors affect corrosion rates, but some studies have found ACQ-treated wood to corrode untreated steel up to four times faster than CCA and to attack galvanized coatings at twice the rate of CCA.
See Rot-Resistant Deck Lumber & Flooring for a disucssion of lumber and flooring alternatives to preservative-treated wood.
Biodegradable Wood Preservatives
A recent addition to wood treatments is Wolmanized® L3 is described as a low-impact, long-lasting preservative treatment with lasting resistance to termites and fungal decay. - Thanks to deck expert Mark Morsching, Everlast for this update, October 2010. (see Deck & Porch Products, Manufacturers) below.
Deck & Porch Resources, Products, Manufacturers: Where to Buy
See Deck & Porch Products, Manufacturers for our complete/updated listings of manufacturers of porch & deck products, materials, coatings, fasteners, lumber, tools.
Deck & Porch Wood Treatment Companies
Arch Wood Protection, Arch Wood Protection, Inc., Arch Treatment Technologies, Inc., 5660 New Northside Dr., Suite 1100
Atlanta, GA 30328, (678) 627-2000- http://www.archchemicals.com
Osmose, Inc. 1016 Everee Inn Road, Griffin, Georgia 30224,
Phone: (770) 233-4200 Fax: (770) 229-5225http://osmosewood.com/,
Chemical Specialties www.treatedwood.com
ACQ-treated wood products with optional water repellent
Suppliers of Composite Structural Lumber for Decks & Porches
U.S. Plastic Lumber, Boca Raton, FL www.usplasticlumber.com Trimax and Durawood structural plastic lumber
Composite Decking System Suppliers
Certainteed Corp. www.certainteed.com Boardwalk solid composite decking with hidden fasteners and optional railing system
Composite Building Products International www.xtendex.com Xtendex hollow composite decking system with optional railing
Correct Building Products www.correctdeck.com Solid composite decking with hidden fasteners and optional railing system
Fiber Composites www.fibercomposites.com Fiberon solid composite decking and optional railing system
Kadant Composites www.geodeck.com Geodeck hollow composite decking and railing system
Kroy Building Products www.kroybp.com Timberlast solid composite decking with optional hidden fastening system
Louisiana-Pacific Corp www.weatherbest.lpcorp.com. WeatherBest solid composite decking, railings, and accessories
Nexwood Industries Limited www.nexwood.com Hollow composite decking and railing systems
Tendura www.tendura.com TenduraPlank solid tongue-and-groove composite flooring for porches; natural finish or primed for painting
Thermal Industries www.thermalindustries.com Dream Composite solid tongue-and-groove composite decking system with optional vinyl railings
TimberTech Limited www.timbertech.com Floorizon hollow composite decking system, solid composite decking planks, and optional railing system
Trex Company www.trex.com Solid composite decking
Weyerhaeuser Building Products www.choicedek.com ChoiceDeck solid composite lumber and optional railings
Hidden Deck Fastener Suppliers
BEN Manufacturing www.premier1.net/~ben69 Dec-Klips fit between deck planks with prongs into edges; nailed into top of joists; electrogalvanized steel
Blue Heron Enterprises www.ebty.com Eb-Ty UV-resistant polypropylene biscuit fits into slots in edge of decking, screws into top of joist Grabber Construction Products www.deckmaster.com Deckmaster angle bracket screws to side of joist and up into decking; available in galvanized or stainless steel
Simpson Strong-Tie www.strongtie.com DBTC deck ties screw down to top of joist with prongs into edges of decking planks; triple-zinc-coated or stainless steel by special order; disposable plastic driving tool
Spotnails www.spotnails.com Tebo stainless-steel fasteners fit between decking boards with prongs into edges of decking; installed with mallet and proprietary tool
TY-LAN Enterprises Inc. www.shadoetrack.com Shadoe Track angle bracket nailed along top of joist and screws up into bottom of deck boards; available in galvanized, powder-coated, and stainless steel
USP Lumber Connectors www.uspconnectors.com Deck Clip screws into edge of one decking board and locks to next board; requires toenailing one edge of each board
Deck & Porch Industry Associations
American Wood Preservers Association (AWPI) www.awpa.com
California Redwood Association www.calredwood.org
Deck Industry Association www.deckindustry.org
Forest Stewardship Council www.fscus.org Information on certified tropical hardwoods
Rainforest Alliance, Smartwood Program www.rainforest-alliance.org Information on certified tropical hardwoods
Southern Forest Products Association www.sfpa.org
Southern Pine Council www.southernpine.com
Western Wood Products Association www.wwpa.org
Western Wood Preservers Institute www.wwpinstitute.org
-- Adapted with permission from Best Practices Guide to Residential Construction.
See CODES for STAIRS & RAILINGS for details about stair building codes and specifications.
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