What Is the Process Used in Water-Treated Wood?

Treated Wood

• Lumber is chemically treated before hitting store shelves for a wide variety of reasons, including to eliminate harmful substances in the wood, to preserve the life of the wood and to make it more durable and better able to resist decay and disease from microorganisms. The most common type of treatment for lumber is chromated copper arsenate (CCA) treatment, involving the injection of copper, arsenic, chromium and other chemicals deep into the wood cells.

Water and Wood Treatment

• In CCA treatment and in other forms of wood treatment, water is a critical component. Water is used as the actual delivery medium to drive CCA chemicals deep into the wood cells. Water-based preservatives are injected into the wood along with the CCA chemicals. These preservatives react with wood substrate and render the CCA chemicals -- which would otherwise be harmful to humans and animals -- water insoluble and practically incapable of leaching out of the wood. The water-based preservatives also render the surface of the wood better able to hold paint and other finishing materials.

Safety Concerns

• The use of water and heavy metals, such as chromium and arsenic, in wood treatment has been a topic of some concern to groups including the Environmental Protection Agency (EPA). The EPA recommends that arsenic-treated wood should never be used in the construction of materials that come into direct contact with drinking water, such as interiors of reservoir roofs and support beams and truss structures for water containers. Potentially hazardous heavy metals can make their way into the drinking water by way of direct contact, leaching, condensation and other means.

Other Considerations

• Water contamination concerns notwithstanding, lumber treated with water and other chemicals is safe for use in a wide range of woodworking projects. According to the University of Rhode Island Extension, CCA-treated wood is ideal for use as "handrails, sundecks, park benches, stadium seats, boardwalks and playground equipment" since medical studies have concluded that "dermal absorption of inorganic arsenic from pressure treated wood is negligible." In fact, dermal (skin) absorption of potentially harmful chemicals is much more likely when using pentachlorophenol and creosote treated lumber than when using CCA-treated lumber.