pressure-treated wood,wood that has had a liquid preservative forced into it in order to protect against deterioration due to rot or insect attack. The most commonly used preservatives are chromated copper arsenate (CCA) and pentachlorophenol. In the treatment process, finished lumber is placed in large container, which is sealed and filled with the preservative solution. As the pressure in the container is increase, the preservative is forced into the lumber; the excess preservative is drained from the container and recycled. The preservative makes pressure-treated wood suitable for long-term outdoor uses where ordinary wood would soon deteriorate. Because of concerns about the possible leaching of arsenic from CCA-treated wood, the use of such wood in most residential and general consumer construction was ended beginning in 2004. Wood for these uses is now treated with ACQ (alkaline copper quat, a copper oxide–quaternary ammonium compound mixture), copper azole, disodium octaborate tetrahydrate (DOT), or other chemicals.
Wood that has been chemically treated to extend its life, especially when outdoors or in contact with the ground. Chromated copper arsenate was the most common pressure-treated wood until a few years ago, but has now been phased out for most applications because of health and environmental concerns. Other pressure-treating chemicals include ACQ (alkaline copper quaternary), copper azole, and sodium silicate.