Frequently Asked Questions About Treated Wood

Q. What is pressure treatment?
 

A. In pressure treatment, chemical preservatives are forced deep into the cellular structure of the wood in a closed cylinder under pressure. This process enables the preserved wood to maintain a chemical barrier against termites and decay for long periods of time, as shown through more than 40 years of continuous field testing conducted by the U.S. Department of Agriculture Forest Service. Several manufacturers guarantee their treated wood to resist decay and termite attack for 40 years or longer.

Q. What do scientific studies say about the safety of pressure-treated wood?
 

A. Scientific research studies have shown the following:  preserved-wood products last longer than alternative products, and thereby conserve a renewable natural resource;  wood preservatives do not aggressively leach into the ground or waterways, drinking water supplies, or adversely affect marine life;  proper handling and use of preserved wood poses no increased risk of cancer or other illnesses among human, animal, and marine life; and  preserved-wood products have been extensively tested and proved to be more reliable and durable than alternative products which require more energy to produce and may be esthetically unacceptable to consumers.

Q. What types of preservatives are used to treat wood?
 

A. There are three broad classes of wood preservatives used in the pressure-treating process. Wood treated with water-borne preservatives is used in a wide variety of products and applications, indoors and outdoors, for residential, commercial, and industrial structures. Ammoniacal Copper Quat (ACQ), and Ammoniacal Copper Zinc Arsenate (ACZA) are some of the most common water-borne preservatives. Wood products that are pressure treated with water-borne preservatives are used in the construction of residential decking and walkways, fences, gazebos, boat docks, playground equipment, as well as for highway noise barriers, sign posts, utility poles, and retaining walls.  Wood pressure treated with creosote is primarily used for timbers in railroad ties, highway bridges and guardrail posts, as well as for marine structures-bulkheads, docks, and seawalls.  Pentachlorophenol is the most widely utilized of the oil-borne preservatives. Utility poles and crossarms are commonly treated with pentachlorophenol. The vaulted ceilings over sports arenas, indoor swimming pools, churches, and shopping centers frequently use glued-laminated beams treated with pentachlorophenol. Copper naphthenate is also an approved oil-borne preservative.

Q. Why should wood be pressure-treated?
 

A. Wood is a plentiful and economic building material that comes from a renewable resource. However, untreated wood is subject to attack by insects, micro-organisms, and decay by fungi. To ensure structural soundness and long service life, wood must be protected from its natural predators.  This is especially important in hot and humid climates or wherever wood comes into contact with ground or water, since wood is subject to decay and attack.  In short, treated wood provides users a longer-lasting product by extending the service life and the useful life of structures, indoors or outdoors.

Q. Is treated wood harmful to the environment?
 

A. No. The Environmental Protection Agency (EPA) conducted an extensive eight-year study where it determined that the benefits of pressure-treated wood products outweighed any potential risks.  Responsible questions by concerned individuals, government officials, and legitimate scientists have resulted in ongoing research programs and study of treated wood products. These studies have produced-and continue to produce-data that support the safety of these products.

Q. Does treated wood cause cancer in humans?
 

A. No. Laboratory or experimental investigations of the product have not shown that treated wood causes cancer in humans. Epidemiology studies of wood-treatment plant workers and carpenters show no increased risk of cancer as a result of exposure to preservative-treated wood.  In order to confirm that treated wood was not contributing to a cancer hazard in humans, a series of research studies on the health status, including cancer incidence, among workers at wood-treating plants were conducted. By the nature of their profession, wood treaters have the greatest degree of contact with treated wood and wood-treating pesticides and are presumably the population at greatest risk from suffering any adverse health effect as a result of exposure to treated wood.  Three independent studies conducted on wood-preserving workers' long-term health status, and interpreted by professional epidemiologists, provided evidence that people exposed to arsenic and chrome from preserved wood are at no increased health risk because of exposure. The workers, in fact, did not experience illness of any kind-including cancer of any type-at a greater incidence than workers not involved with treated wood.

Q. Is there any reason why treated wood should not be used in gardening projects?
 

A. The extra durability of pressure treatment makes treated wood the perfect product for building raised beds, terraced gardens, grape or tomato stakes, mushroom trays, vineyard supports, retaining walls, trellises, arbors, garden furniture, compost bins, walkway steps, flower bed edging, or planters. Any assertion that gardeners should not grow edibles in planters or raised beds made with treated wood is without basis.  Independent research conducted by county extension agents in Texas, in cooperation with Texas A&M's Laboratory and Southwest Research Institute, has concluded that both creosote and water-borne treated wood are not harmful in garden use. In tests on water-borne-treated wood, the treated timbers varied in age from six months to nine years. Arsenic levels in soil samples taken from the garden were no more than what occurs naturally in any soil. Further, the levels of arsenic one inch from the timbers and 12 inches from the timbers were the same, indicating no migration of the preservative from the timbers.  Pentavalent arsenate, the kind used in wood preservatives, should not be confused with commercially produced trivalent arsenic, which is not used in any wood preservative. Pentavalent arsenate occurs naturally in the soil, water, air, plants, and in most living creatures-including humans.  Finally, in tests of creosote-treated wood, no creosote was detected at a threshold of 660 parts per billion.

Q. Should treated wood be kept away from food and water?
 

A. Incidental contact of treated wood with drinking water, as with piling, docks, piers, or bridges, is acceptable. However, treated wood should not be used where it is likely to become a component of food or animal feed, or where the wood is likely to mix directly with foodstuffs.  Treated wood should not be used as kitchen countertops or food cutting boards. The Food and Drug Administration  (FDA) does not recommend using any wood for kitchen countertops or food cutting boards, because food may become trapped in the knife cuts in the board, allowing bacteria to grow and creating an unsanitary environment.

Q. Is it safe for our children to play in playgrounds where treated wood has been used to construct fences and playground equipment, and is it safe to walk barefoot on pressure-treated backyard decking?
 

A. Water-borne preservatives are recommended for treating playground equipment. There is no reason to avoid using wood treated with a water-borne preservative in the playground environment, or to avoid touching or walking barefoot on pressure-treated backyard decks. In fact, wood that has been pressure treated is safe and widely used for playground equipment and decking.  A water-repellent or wood sealer may be applied periodically to reduce cracking and splitting and thus the likelihood of children getting splinters.  Creosote and penta-treated woods are not recommended for use in playground equipment.

Q. How do I know that I am purchasing properly treated wood?
 

A. To be certain that that the material for your outdoor project is of a quality to meet its intended use, follow these guidelines when purchasing or specifying treated lumber:  Wood products treated with waterborne preservatives should conform to the approved treating industry standards set forth by the American Wood-Preservers' Association (AWPA) and the American Lumber Standards Committee (ALSC). This certification will be indicated by either an ink stamp (in addition to the lumber grade) or more commonly by a plastic tag stapled to the end of the lumber.  The required information within the treated quality mark includes the logo of the accredited inspection agency, the AWPA Standard utilized in the treating process, the preservative retention level and intended end-use/application, and the name of the treating plant. AWPA has developed different levels of preservative retention, based on the material's intended use. For waterborne preservatives, the following levels of preservative retention for specific applications will also be indicated within the quality mark.

 

Retention	Product Application
0.25	Above Ground
0.40	Ground Contact
0.60	(PWF) Permanent Wood Foundation
2.50	Salt Water

 

Important note: The presence of a plastic end-tag does not necessarily indicate certified treated lumber. The quality mark should be printed separate from the manufacturers' warranty and guarantee information. Always look for the TP logo or AWPA gaurantee for quality.

Q. How do I know the lumber which I buy has been properly treated?
 

A. If you purchase pressure treated lumber which carries the TP (Timber Products) stamp on the lable then you can be assured that the lumber has been treated to pass the minimum standards of two different teating processes. One test provides for the assurance that the lumber as passed a retention test. This means that all lumber with a .40 designation or the words ground contact on the end tag will have a minimum of 40 percent of chemical concentration in the wood. Most of the time that amount will be higher. The other test gaurantees that the chemicals have penetrated deeply into the surface of the wood. Boring samples of 2-1/2 inches are made in every treatment charge to insure that the treatment is sufficient. TP can gaurantee the quality of these products because they send inspectors to the treatment plants every month to test and qualify the lumber which is sold to the lumber yards and then to you the consumer. If the lumber does not pass these two tests, then the lumber has to be re-treated until it does. Not all lumber yard buy pressure treated lumber from treatment plants which must meet these rigorous guidelines.

Q. Does the EPA recommend the use of additional safety equipment while working with pressure-treated wood?
 

A. No. The use of standard safety equipment reflects good industrial common sense when working with all types of building materials. Eye protection, dust mask, and gloves should be used when sawing or machining any type of building material, including wood products, treated or untreated. Practicing good personal hygiene at the completion of any construction project also applies.

Q. Does water-borne treated lumber need to be painted, stained, or waterproofed?
 

A. A water repellent sealer should be applied to slow initial shrinkage as the wood comes into equilibrium with the environment (see manufacturer's recommendations for details on application). Many treated-wood products are now available with water repellence built in through the addition of water repellents to the preservative solution. Treated wood should be cleaned and re-sealed yearly to maintain optimum appearance. Unprotected treated lumber will begin to change color as a result of the wood's reaction to ultraviolet (UV) rays of the sun. Sealants with UV inhibitors will slow the color change.

Q. How long should I wait before I paint or stain my deck?
 

A. Even though the lumber may be kiln-dried before treatment, using water-borne preservatives restores moisture to the wood. Too much moisture in the wood may prevent the stain or paint from penetrating the wood sufficiently. It is best to test the wood by painting or staining a scrap piece to see if it applies properly. If not, wait until it does. A water repellent should be applied annually. Do not use latex paints. Semi-transparent, oil-based stains work best. If you do not have time to wait, purchase wood marked "KDAT" (Kiln-dried after treatment).

Q. Why is pressure-treated wood an ideal replacement for concrete, plastics, steel, and aluminum in many uses?
 

A. Steel, concrete, and aluminum could be substituted for some uses, but this will result in much higher costs in applications where treated wood is now used, higher energy requirements in the process of creating substitute material, greater air and water pollution and/or environmental protection costs, and higher dependency on foreign sources for imported materials.  Substitute materials may not be appropriate for some uses-some types of steel may corrode, concrete may deteriorate in salt water, and plastic may not have the strength, durability, and structural integrity. Since wood is a renewable resource, modern forest managers can ensure a continuous and plentiful supply.  There is an added benefit. Wood preservation for commercial and industrial application extends the nation's forest resources by reducing costly and unnecessary replacement. And finally, it is easy to make on-site modification to wood structures.

Q. How should you dispose pressure-treated wood?

A. First, it is important to remember that pressure-treated wood is not a pesticide, is not a hazardous product, and has not been listed as hazardous waste.  It is completely proper and legal to send treated wood to a landfill. However, due to the growing shortage of landfill space, many industrial users are selecting recycling of treated wood as their disposal option.  There is a growing movement to "manage" the disposal of treated wood. In many cases, the wood can be reused in its original form or used in secondary applications such as fence posts, landscaping, and other projects.  Treated wood should not be burned in fireplaces, stoves, or other non-permitted units because toxic materials may be produced as part of the smoke or ashes.

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