Pressure Treated Saltwood
by James B. “Jim” Kea
Area Extension Forestry Agent – now retired
Thursday, February 9th, 2006
As warm weather returns, many homeowner’s thoughts are turning to outdoor building projects. Pressure treated southern yellow pine can be the ideal material to use for that deck, fence, or tree house. Pressure treated wood is regular wood which has been impregnated with preservative chemicals. The chemicals are forced deep into the wood to make it resistant to rot, insects, and even marine borers. Three major types of wood preservatives are use for pressure treatment in North Carolina. When properly applied, they will all increase the life of fence posts or decks to 25 years and longer. They are all resistant to most types of rot and insects.
The most widely used preservative in and around homes is chromated-copper-arsenate (CCA). The treated wood is odorless, usually light-greenish/brown in color, and can be painted or stained when dry. A water repellant treatment will reduce checking and splitting. It is recommended for all uses around the home including decks, fencing, plant boxes, greenhouses, and plant stakes.
When you purchase pressure treated wood, look for a “quality mark.” This stamp includes the American Wood Preservers Bureau (AWPB) logo, the name of the treatment company, and the level of treatment – ground contact, above ground, or foundation. Some wood is also stamped “dry.” This means that is has been dried after treatment. Dried wood is desirable where straightness and uniform size are important. The quality mark is the homeowner’s guarantee of quality and do-it-yourselfers are encouraged to purchase wood that carries it.
Some homeowners are concerned about the safety of arsenic containing preservatives. Several studies have shown that the chemical is fixed in the wood. It stays in the wood even when it is in the ground or in water. The Environmental Protection Agency has approved CCA treated wood for exposed foundation walls and other uses around the home providing that it is free of visible surface deposits. Homeowners should not, however, burn scraps of treated wood because soluble arsenic will remain in the ashes. EPA also advises against using salt treated wood for cutting boards or in other applications in which wood may become incorporated in food.
UPDATE: Industry has agreed to remove CCA pressure treated wood from retail markets in 2003. EPA agreed to the move noting CCA material is still safe. CCA treated wood will still be available for commercial applications such as marine construction. Industry cited more viable alternatives plus loss of consumer confidence due to fact-less media reporting.
Creosote and pentachlorophenol are the two other preservatives used for pressure treatment. These are excellent for fencing and other outdoor uses, but should not be used in building or other enclosed spaces. Wood freshly treated with either of these two preservatives should not be used close to plants because of the risk of plant burn.
Some simple precautions should be taken when building with pressure treated wood. Gloves should be worn when handling creosote and pentachlorophenol treated wood. Protective goggles and a dust mask are advised when power sawing treated wood. Finally, hands and other exposed skin areas should be washed before eating and when you have finished the project. If treated wood is cut or bored after treatment, it is recommended that the fresh cut ends be brushed with a wood preservative solution if they will be in the ground or regularly wetted. This provides extra protection to the cut surfaces. Pressure treated southern yellow pine is a versatile, attractive, and easy material to use. Many building material suppliers provide plans and suggestions for do-it-yourself projects. Contact them or your County Extension Office if you would like more information on pressure treated wood.
The heartwood of a few tree species is naturally resistant to attack by wood-destroying organisms. Heartwood is usually dark and is found in the center of the tree stem. Its darkness is caused by chemicals called extractives that impart a natural resistance to attack. Some species of trees have a considerable natural resistance to attack owing to high quantities of these chemicals in the wood. In contrast, the light-colored sapwood of the tree has virtually no natural resistance; it will deteriorate rapidly under conditions favorable to the growth of wood- destroying organisms. The problem with nonresistant sapwood is further complicated because the heartwood and sapwood of some species are practically indistinguishable. Also, the trees being cut today have a much smaller percentage of heartwood than did the old-growth trees of yesteryear.
Southern species which have attack-resistant heartwood include the cedars, black locust, red mulberry, osage orange, and old-growth cypress.
Old growth bald cypress was once considered a highly durable species. Research has shown that today’s second growth cypress is not naturally durable.
Wood cut from several western trees, including redwood and western red cedar, is often considered to be naturally durable. However, when these species are used in the South, the durability of the wood is, at best, variable. Much of the wood cut from these species will decay or succumb to termites in just a few years.