ABCs of pressure treated wood industry

THE PRESSURE treated wood industry is adding I new terms and words to the building materials vocabulary. This glossary will help the retailer to be better informed.

Air-Dried - Drying of lumber by exposure to air. Lumber may be either covered or uncovered. (See Seasoning & Moisture Content)

Annual Growth RingA layer of wood growth added to a tree in a single growing season. These can usually be seen on the ends of boards.

ACA, ACCSee Preservatives.

AWPAAmerican Wood Preservers Association. An organization to provide information on pressure treating standards, quality control programs and other technical assistance.

AWPBAmerican Wood Preservers Bureau. The group that certifies pressure treating companies and assures product consistency and reliability. Also administers the AWPA quality-assurance lumber stamping program. Lumber stamped with the AWPB mark meets the standards for the particular level of pressure treatment indicated on the stamp.

AWPIAmerican Wood Preservers Institute. A marketing and communications organization comprised of companies in the pressure treated wood industry. Communicates with the general public and interested professionals about pressure treated wood products.

Assay (retention by)The determination of preservative retention in treated wood by analysis of samples of wood. Usually expressed in pounds per cubic foot (pcf) or kilograms per cubic meter (kglm3).

Board FootA standard measurement of lumber. One board foot is represented by a board I ft. long, l2 in. wide, and I in. thick or its cubic equivalent. Generally, lumber I in. or more in thickness has board footage calculated on the nominal (rather than actual) thickness of the board.

CellGeneral term for the structural units of plant tissue, such as wood fibers. In pressure treating, chemical preservatives penetrate the cells of the wood to protect them from attack by insects and decay.

CCASee Preservatives.

CreosoteSee Preservatives.

Cylinder, TreatingA steel tank, usually horizontal, which may be opened and closed at one or both ends. Wood is placed in the cylinder for treatment, usually by a pressure process in which chemicals are introduced into the cylinder. Also called a Retort.

DecayDecomposition of wood substance by wooddestroying fungi. Occurs where wood is exposed to moisture and air in a temperate climate. Also called rot, and erroneously referred to as "dry rot."

DurabilityLasting qualities or permanence in service of wood. Decay and insect resistance is more specific term, indicating resistance to attack by wood-destroying fungi and termites under conditiorrs favorable to their growth.

Fiber Saturation PointThe stage in the drying or wetting of wood at which the cell walls are saturated and the cell cavities are free from water. For most woods, this occurs at about 3090 moisture content. (See Moisture Content)

FungiTiny organisms that attack wood, using wood fibers as food when conditions of climate (air, moisture) are right. On the surface of lumber, fungi can darken the wood and make it slippery. Can cause severe deterioration of wood and the structural quality of lumber. In some areas, significant destruction of wood can occur in as few as 3-5 years.

Grsde MarkIdentification of lumber with symbols of lettering to certify its quality of grade. Usually administered according to standards set by a lumber organization. Grade is based on the presence or absence of defects, such as knots, checks, decay, etc.

Green Wood - Freshly sawed or undried wood.

HesrtwoodThe wood extending from the pith (center) of the tree to the sapwood (newer wood fibers). The cells of the heartwood no longer participate in the life processes of the tree. Usually darker than sapwood.

InsectsMost commonly, termites which attack wood, using it as food.

Story at a Glance

Pressure treated wood terms . industry associations . . preservalive chemicals standards.

IncisingPuncturing the lateral surfaces of lumber or poles with knives as an aid to more uniform penetration of chemical preservatives.

Kiln-DriedLumber dried in a kiln using artificial heat. Process used to dry lumber to a moisture content below that obtained in air-drying. Drying device is called a "dry kiln."

Laminated Wood - Layers of wood glued (usually) together with grain direction essentially parallel to the longitudinal direction of the assembly. Sometimes called a "glulam." Manufacturing process used to achieve a piece of lumber (sometimes called a "beam") larger than that obtainable with sawn lumber, or specifically designed for a certain application, such as a long span or unusual strength requirement.

Moisture ConlentThe weight of water contained in wood, usually expressed as a percentage of the oven-dry weight of the wood. Equilibrium Moisture Content is the moisture content at which wood neither gains nor loses moisture when surrounded by air at a given relative humidity and temperature. Varies in different climates.

Lumber is constantly subject to changes in its moisture content. Serious decay can occur in untreated wood when the moisture content is above the 3090 fiber saturation point. Lumber is said to be reasonably protected from decay if it is maintained at a moisture content of l99o or less. This is essentially "dry" lumber.

PoleRound wood or log, generally used as utility poles or for house foundations. Most often pressure treated for durability.

PenetrationThe depth to which preservative chemicals enter the wood.

PentaSee Preservative

Preservative, Oil-borneA wood preservative that is introduced into wood in the form of a solution in oil.

Preservative, WoodIncludes all chemicals or combinations of chemicals that will protect wood against deterioration from decay, insects, marine borers, fire, weathering, absorption of water and chemical action. Some commonly used preservative chemicals include: ACAammoniacal copper arsenite; ACCacid copper chromate; Creosotetar distillate; PentaPentachlorophenol dissolved in a hydrocarbon solvent; CCA -

Chromated copper arsenate. These chemicals will leave wood with a greenish tint, a natural brown color, or, in the case of creosote, a dark brown to black color.

Pressure TreatmentProcess of treating wood in a closed container where preservative or fire retardant is forced into the wood under pressure. Pressure is generally preceded or followed by vacuum.

Quality ControlIn pressure treating, the AWPB administers a quality control and inspection program that includes a quality wood-marking program to assure that treated wood will perform well in the use for which it was intended. Basically, lumber is treated to two different preservative retention and penetration levels: one for inground use (LP-22 mark) and one for lumber used above the ground (LP-2 mark).

RetortSee Cylinder, Treating.

RetentionSee Assay.

RotSee Decay.

SapwoodWood of pale color near the outside of the log. Under most conditions, the sapwood is more susceptible to decay than heartwood, and a log usually has a higher percentage of sapwood than heartwood. No species of wood has sapwood that is naturally resistant to decay and insects.

SeasoningAlso known as "Drying." The removal of moisture from green wood to improve its serviceability. Can be accomplished by either air-drying or kilndrying. Seasoned wood will shrink less than unseasoned wood.

ShrinkageAs wood loses moisture, it shrinks. Essentially, wood does not shrink when it is above the fiber saturation point. Wood shrinks most in the direction of the annual growth rings (tangentially) and shrinks only about half as much across the rings (radially). It shrinks only slightly along the grain (longitudinally). This dimensional instability of wood below the fiber saturation point can distort the shape of wood pieces depending on the curvature of the annual rings. Kiln-drying minimizes the distortions that shrinkage can cause.

SAWPSociety of American Wood Preservers, Inc. An industry group which provides information on pressure treating standards, quality control programs and other technical assistance.

SPTASouthern Pressure Treaters Association. Industry group of professionals able to provide information on standards, quality control, technical assistance.

StrengthThe ability of a wood member to sustain stress without structural failure. Decay and insect attack signficantly reduce the strength of wood over a period of time. Some building codes require pressure treated wood for important structural members outdoors, because treating adds long-term durability to the wood, assuring the structural strength of the project.

ETechnical Support

The American Wqrd-Prerervers' Assmiation ( AWPA) issues treatment

The American Wood Preservers Bureau (AWPBI issues quali(y contr()l standards for presure treated lumber and plywood. The AWPB prtrgram is putterned after the well established lumber grade mark sys(em. The AWPB quality mark on each piece of pressure treated lumber and plywood is the consumers assurance that the trealment complies with established standards.

TYPICALAWPB QUAUry MARK IS:

GROUND CONTACT LP-22

Wood Preserving

ARLINGTON. VA.

A Year of treatmenl

B American Wmd Preservers Bureau lrademark

C The preservative used for treatnrenl

D The applicable American Wood Preservers Bureau quality standard

E Trademark of the agency supervising the lrealing plant

F Proper exposure conditions

G Treatrng c,tmpilny Jn(l plant l()(Jli"n

Treating PressurePressure used in injecting the preservative into wood, usually expressed in pounds per square inch (psi).

Trertment, BrushApplication of a liquid preservative to the surface of lumber with a brush. Pressure treatment is far more effective in protecting the wood than brush treatment (or "dipping") since the pressure process locks the preservatives deeper into the wood cells. Surface treatments will weather away in a short time. Brush treatment is, however, used on cut ends of lumber that has been pressure treated as an additional protective measure easily applied in the field.

UnderstructureThe important structural portion of a project such as a deck. Consists of posts, joists, stringers, etc. that support the decking. Pressure treated wood is ideal for understructures, since it is economical and its durability is more uniform and dependable than "naturally durable" species of wood.

Wood PreservationTreatment of wood with chemical preservatives which reduce susceptibility to deterioration by fungi, insects, or marine borers. Extending service life of outdoor wood projects through wood preservation extends our forest resources by making replacement of projects less frequent.