Science Fair Project Encyclopedia
Lumber is supplied either rough or finished. Rough lumber is the raw material for furniture making and other items requiring additional cutting and shaping. It is available in many species, usually hardwoods. Finished lumber is supplied in standard sizes, mostly for the construction industry, and is primarily one of a few coniferous needle-bearing species such as pine, hemlock, fir or spruce.
Rough lumber comes from the sawmill without further cutting or shaping. It is usually sold in random lengths and widths and measured in the USA in board feet, a unit of 1 inch x 1 inch x 1 foot. It is available air-dried or kiln-dried. Air-dried lumber is carefully stacked and allowed to dry for several months, depending on thickness. It is used for some outdoor purposes, such as building sheds and fences. Kiln-dried wood is stacked and dried in moisture- and temperature-controlled kilns built for the purpose. It is then ready to be used for furniture-making or other woodworking uses.
Finished lumber is usually kiln-dried then planed and cut to predetermined sizes, primarily for use by the construction industry. When using Imperial measurements, the widths given are from before planing, whereas the piece actually sold is smaller; a 2×4 for example is actually only 1-1/2 by 3-1/2 inches after planing. Other stock is sized similarly. The lengths are actual sizes and are multiples of 2 feet. Sizes from 8 to 16 feet (8, 10, 12, 14, 16) are commonly available, and larger sizes (18, 20, 22, 24) are sometimes available. When using metric measurements, lumber is measured in actual sizes.
In the USA, timber is cut in the forest in 24 foot lengths. At the mill it is recut into 3-8 foot lengths, an 8 foot and a 16 foot length, a 10 foot and a 14 foot length or 2-12 foot lengths.
Lumber is also used to refer to plywood and composite wood products.
Lumber was one of the first industries in the United States, Maine was an early leading producer; however, later expansion led to Oregon, Washington, and California assuming the lead in domestic lumber production. Logging, the felling and preparation of trees for lumber was a related frontier industry; various tales of lumberjacks were a substantial portion of a certain chapter in North American folklore.
Timber or lumber may be treated with a preservative that protect it from being destroyed by insects, fungus or exposure to moisture. Generally this is applied through combined vacuum and pressure treatment. The preservatives used to pressure-treat lumber are classified as pesticides. Treating lumber provides long-term resistance to organisms that cause deterioration. If it is applied correctly, it extends the productive life of lumber by five to ten times. If left untreated, wood that is exposed to moisture or soil for sustained periods of time will become weakened by various types of fungi, bacteria or insects. Also see timber treatment.
- Chromated copper arsenate (CCA). An extremely common preservative developed in the 1930s. In CCA treatment, copper is the primary fungicide, arsenic is a secondary fungicide and an insecticide, and chromium is a fixative which also provides ultraviolet (UV) light resistance. Recognized for the greenish tint it imparts to lumber, CCA is a preservative that was extremely common for many decades, however it contained arsenic. The chemicals may leach from the wood into surrounding soil, resulting in concentrations higher than naturally-occurring background levels. A study cited in Forest Products Journal found 12-13 percent of the chromated copper arsenate leached from treated wood buried in compost during a 12-month period. Once these chemicals have leached from the wood, they are likely to bind to soil particles, especially in soils with clay or soils that are more alkaline than neutral. In the United States on 1 January 2004 the Environmental Protection Agency (EPA) began restricting the use of CCA in treated lumber in residential and commercial construction, with the exception of shakes and shingles, permanent wood foundations, and certain commercial applications. This was in an effort to reduce the use of arsenic and increase environmental safety. However some consumer outlets such as Home Depot were still reported to be selling CCA lumber long after the ban went into effect.
- Alkaline copper quaternary (ACQ). This preservative is made up of copper, a fungicide, and quaternary ammonium compound (quat), an insecticide which also augments the fungicidal treatment. Since it contains high levels of copper, ACQ-treated lumber is five times more corrosive to common steel, according to American Wood Preservers Association (AWPA) test results. It is necessary to use double-galvanized or stainless steel fasteners in ACQ lumber. The U.S. began mandating the use of ACQ in end-consumer lumber in 2004.
- Other copper compounds. These include copper azole (CA), copper chromate, copper citrate, acid copper chromate, and ammoniacal copper zinc arsenate (ACZA). The CA treatment is an alternative to ACC and ACQ in the United States and Canada. AZCA is generally used for marine applications.
- Borate preservatives. Unlike most other preservatives, borate compounds do not become fixed in the wood and can be washed out. Therefore they cannot be used where they will be exposed to water.
- Oil-based preservatives. These include pentachlorophenol, copper naphthenate , and creosote. All of them are toxic and are generally not used in consumer products. Creosote is a tar-based preservative, that was commonly seen on telephone poles, before it was withdrawn from production due to toxicity.
- Naturally rot-resistant woods. This includes Western Redcedar, many cypresses, and Coast Redwood. These species are resistant to decay in their natural state, due to high levels of organic chemicals called 'extractives', mainly polyphenols. Extractives are chemicals that are deposited in the heartwood of certain tree species as they convert sapwood to heartwood. However these species tend to be prohibitively expensive for general construction applications.
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