Pressure treated wood grows in acceptance, use

By Harry Anton Regional Representative WWPA Field Services Dept. Marletta, Ga.

has grown rapidly in acceptance and use during the past five years, and now is being used structurally and non-structurally in fences, decks, farm buildings, marine structures and in the residential wood foundation.

Wood is man's most versatile product, but because it is a natural product it is subject to decay and insect attack. These natural enemies can greatly affect the seivice life and strength of wood products. Chemicalpreservatives are one way to make wood resistant to fungus growth and insect attack.

Fungi need four general conditions to live and cause decay: (1) proper temperature, generally between 50 and 90 degrees; (2) moisture content in excess of20c/o; (3) air, particularly oxygen, and (4) a food source, such as wood fiber. Pressure treatment of wood fiber eliminates it as a food source.

RESSURE-TREATED woodto describe its CCA treated lumber. Other companies use names such as "Green Salt" and "Langwood." Whatever the trade name, the lumber is treated with CCA salt compound. Different levels of protection are provided by pressure-treated wood. The American Wood Preservers Bureau (AWPB) writes standards for presure treating for various species of wood with different types of chemicals and treating processes, including the water-borne CCA pressure treatment. AWPB also provides a quality control program which checks to make sure that treated lumber is properly treated. Standards whichretailers should be aware of are LP-2 for above ground use, such as fences and deck boards; or LP-22 for ground contact for such as fence posts, or for immersion such as dock pilings; and the FDN Standard for use in the wood foundation. These three standards are differentiated by the amount of chemical preservatives retained in the wood. The LP-22 standard requires more chemicals, .40 pounds per cubic foot of wood, and the FDN Standard requires even more chemicals, .60 per cubic foot.

The most common types of pressure chemical treatments sold today by retailers are known as the "waterborne salts." They are most preferred becausetheyleavethe treated surface relatively clean, paintable, and odor free, and can be used both inside and out.

There are a number of different water-borne preservatives available to the treater, but the one most commonly used is CCA, chromated copper arsenate. The copper base gives the wood a green color and makes it easy to recognize from untreated wood. CCA treated lumber is known by different trade names. The Koppers Company uses the term "Outdoor Wood" and "Wolmanizing" to describe its CCA treated lumber. The Osmose Company uses the names "All-Weather Wood," "AllSeasons Wood," or "Osmose K-33,"

In addition to the chemical retention requirements, AWPB or other

Story at a Glance

Pressure treated wood continues to gain acceptance. .. different treating standards for different uses. retailer should know best specles tol customer.

quality control agencies must check for additional treating requirements, including the depth of chemical penetration, the moisture content of the wood at the time of treatment (25 moisture content, 25 MC, or less), the percentage of heartwood and sapwood Oeartwood is very difficult to treat), and the species of wood being treated. Due to natural characteristics, some species treat better than others.

CCA waterborne salt treatments work best on species which are mostly sapwood. Ponderosa pine, Southern yellow pine and, around the Great Lakes, red (Norway) pine are used almost exclusively for CCA treatment. These three species do not require "incising" to accept the proper amount of chemicals for treatment, so they give a nicer appearance after treatment. All other species require the cutting of tiny holes in the surface of the wood, incising, for proper treatment levels.

Treated lumber is identified by a "quality mark" much the same as lumber is identified by agrade stamp. A quality mark identifies the treater, the quality control agency, standards used for treating, the type of chemicals used, and in what year it was treated. The quality marks assure the dealer, the user, and other interested parties, such as building inspectors, that this is properly treated for its intended use.

Because the CCA chemicals are carried into the wood by water, all treated lumber should be re-dried to its original moisture content level. Lumber that is "kiln dried after treatment" (KDAT) will maintain stability and have a dry, paintable surface. All dry, treated lumber

That's the working philosophy of the Western Wood Products Association Quality Standards department and its chief lumber inspector, William R. Spannaus, who's responsible for administering the quality control procedures that in a normal year cover some 12 billion board feet of lumber.

WWPA is both a rules-writing and an inspection agency, certified bythe Board of Review of the American Lumber Standards Committee. The WWPA gradestamp is a familiar sight nationwide in retail yards and building sites.

WWPA is authorized by the ALSC to write rules for Western lumber, and it does so through the WWPA Quality Standards Committee.

In this role it develops, writes and publishes grading rules covering species and species groupings dominant to the Western woods region. It also provides engineering support and research into wood properties, to assist in development of working stresses. It also writes rules and conducts research for quality control programs for such special products as machine stress-rated and glued lumber. Inherent in the rules-writing process is obtaining building code approvals for official WWPA rules.

Direct oversight of the ruleswriting function at WWPA is provided by its Quality Standards Committee, representing grading mills from throughout the l2-state Western Wood Region. William Ford, BoiseCascade Corp., Portland, Or., is the committee's current chairman.

As an inspection agency, WWPA serves mills that produce 400/o of U.S. lumber production in a normal year. It does so with a team of trained lumber inspectors positioned