Adherend. A body that is held to another body by an

Adhesion. The state in which two surfaces are held together
by interfacial forces, which may consist of valence forces or
interlocking action or both.

Adhesive. A substance capable of holding materials together
by surface attachment. It is a general term and includes cements,
mucilage, and paste, as well as glue.

Assembly Adhesive—An adhesive that can be used for
bonding parts together, such as in the manufacture of a
boat, airplane, furniture, and the like.

Cold-Setting Adhesive—An adhesive that sets at temperatures
below 20 °C (68 °F).

Construction Adhesive—Any adhesive used to assemble
primary building materials into components during building
construction—most commonly applied to elastomer-based
mastic-type adhesives.

Contact Adhesive—An adhesive that is apparently dry
to the touch and that will adhere to itself instantaneously
upon contact; also called contact bond adhesive or dry
bond adhesive.

Gap-Filling Adhesive—An adhesive capable of forming
and maintaining a bond between surfaces that are not
close fitting.

Hot-Melt Adhesive—An adhesive that is applied in a
molten state and forms a bond on cooling to a solid state.

Hot-Setting Adhesive—An adhesive that requires a temperature
at or above 100 °C (212 °F) to set it.

Room-Temperature-Curing Adhesive—An adhesive
that sets in the temperature range of 20 to 30 °C (68 to
86 °F), in accordance with the limits for Standard Room
Temperature specified in the Standard Methods of Conditioning
Plastics and Electrical Insulating Materials for
Testing (ASTM D 618).

Solvent Adhesive—An adhesive having a volatile organic
liquid as a vehicle. (This term excludes water-based

Structural Adhesive—A bonding agent used for transferring
required loads between adherends exposed to service
environments typical for the structure involved.

Air-Dried. (See Seasoning.)

Allowable Property. The value of a property normally
published for design use. Allowable properties are identified
with grade descriptions and standards, reflect the orthotropic
structure of wood, and anticipate certain end uses.

Allowable Stress. (See Allowable Property.)

American Lumber Standard. The American Softwood
Lumber Standard, Voluntary Product Standard PS–20 (National
Institute of Standards and Technology), establishes
standard sizes and requirements for the development and
coordination of lumber grades of various species, the assignment
of design values when called for, and the preparation
of grading rules applicable to each species. It provides for
implementation of the standard through an accreditation and
certification program to assure uniform industry-wide marking
and inspection. A purchaser must, however, make use of
grading association rules because the basic standards are not
in themselves commercial rules.

Anisotropic. Exhibiting different properties when measured
along different axes. In general, fibrous materials such as
wood are anisotropic.

Assembly Joint. (See Joint.)

Assembly Time. (See Time, Assembly.)

Balanced Construction. A construction such that the forces
induced by uniformly distributed changes in moisture content
will not cause warping. Symmetrical construction of
plywood in which the grain direction of each ply is perpendicular
to that of adjacent plies is balanced construction.

Bark Pocket. An opening between annual growth rings that
contains bark. Bark pockets appear as dark streaks on radial
surfaces and as rounded areas on tangential surfaces.

Bastard Sawn. Lumber (primarily hardwoods) in which the
annual rings make angles of 30° to 60° with the surface of
the piece.

Beam. A structural member supporting a load applied transversely
to it.

Bending, Steam. The process of forming curved wood
members by steaming or boiling the wood and bending it to
a form.

Bent Wood. (See Bending, Steam.)

Bird Peck. A small hole or patch of distorted grain resulting
from birds pecking through the growing cells in the tree.
The shape of bird peck usually resembles a carpet tack with
the point towards the bark; bird peck is usually accompanied
by discoloration extending for considerable distance along
the grain and to a much lesser extent across the grain.

Birdseye. Small localized areas in wood with the fibers indented
and otherwise contorted to form few to many small
circular or elliptical figures remotely resembling birds’ eyes
on the tangential surface. Sometimes found in sugar maple
and used for decorative purposes; rare in other hardwood

Blister. An elevation of the surface of an adherend, somewhat
resembling in shape a blister on human skin; its boundaries may be indefinitely
outlined, and it may have burst and become flattened. (A blister may be caused
by insufficient adhesive; inadequate curing time, temperature, or pressure;
or trapped air, water, or solvent vapor.)

Bloom. Crystals formed on the surface of treated wood by
exudation and evaporation of the solvent in preservative

Blow. In plywood and particleboard especially, the development
of steam pockets during hot pressing of the panel,
resulting in an internal separation or rupture when pressure
is released, sometimes with an audible report.

Blue Stain. (See Stain.)

Board. (See Lumber.)

Board Foot. A unit of measurement of lumber represented
by a board 12 in. long, 12 in. wide, and 1 in. thick or its
cubic equivalent. In practice, the board foot calculation for
lumber 1 in. or more in thickness is based on its nominal
thickness and width and the actual length. Lumber with a
nominal thickness of less than 1 in. is calculated as 1 in.

Bole. The main stem of a tree of substantial diameter—
roughly, capable of yielding sawtimber, veneer logs, or large
poles. Seedlings, saplings, and small-diameter trees have
stems, not boles.

Bolt. (1) A short section of a tree trunk. (2) In veneer production,
a short log of a length suitable for peeling in a

Bond. (1) The union of materials by adhesives. (2) To unite
materials by means of an adhesive.

Bondability. Term indicating ease or difficulty in bonding a
material with adhesive.

Bond Failure. Rupture of adhesive bond.

Bondline. The layer of adhesive that attaches two

Bondline Slip. Movement within and parallel to the bondline
during shear.

Bond Strength. The unit load applied in tension, compression,
flexure, peel impact, cleavage, or shear required to
break an adhesive assembly, with failure occurring in or
near the plane of the bond.

Bow. The distortion of lumber in which there is a deviation,
in a direction perpendicular to the flat face, from a straight
line from end-to-end of the piece.

Box Beam. A built-up beam with solid wood flanges and
plywood or wood-based panel product webs.

Boxed Heart. The term used when the pith falls entirely
within the four faces of a piece of wood anywhere in its
length. Also called boxed pith.

Brashness. A condition that causes some pieces of wood
to be relatively low in shock resistance for the species and,
when broken in bending, to fail abruptly without splintering
at comparatively small deflections.

Breaking Radius. The limiting radius of curvature to which
wood or plywood can be bent without breaking.

Bright. Free from discoloration.

Broad-Leaved Trees. (See Hardwoods.)

Brown Rot. (See Decay.)

Brown Stain. (See Stain.)

Built-Up Timbers. An assembly made by joining layers of
lumber together with mechanical fastenings so that the grain
of all laminations is essentially parallel.

Burl. (1) A hard, woody outgrowth on a tree, more or less
rounded in form, usually resulting from the entwined growth
of a cluster of adventitious buds. Such burls are the source
of the highly figured burl veneers used for purely ornamental
purposes. (2) In lumber or veneer, a localized severe
distortion of the grain generally rounded in outline, usually
resulting from overgrowth of dead branch stubs, varying
from one to several centimeters (one-half to several inches)
in diameter; frequently includes one or more clusters of several
small contiguous conical protuberances, each usually
having a core or pith but no appreciable amount of end grain
(in tangential view) surrounding it.

Butt Joint. (See Joint.)

Buttress. A ridge of wood developed in the angle between a
lateral root and the butt of a tree, which may extend up the
stem to a considerable height.

Cambium. A thin layer of tissue between the bark and
wood that repeatedly subdivides to form new wood and bark

Cant. A log that has been slabbed on one or more sides.
Ordinarily, cants are intended for resawing at right angles
to their widest sawn face. The term is loosely used. (See

Casehardening. A condition of stress and set in dry lumber
characterized by compressive stress in the outer layers and
tensile stress in the center or core.

Catalyst. A substance that initiates or changes the rate of
chemical reaction but is not consumed or changed by the

Cell. A general term for the anatomical units of plant tissue,
including wood fibers, vessel members, and other elements
of diverse structure and function.

Cellulose. The carbohydrate that is the principal constituent
of wood and forms the framework of the wood cells.

Cellulosic Fiberboard. (See Wood-Based Composite

Check. A lengthwise separation of the wood that usually
extends across the rings of annual growth and commonly
results from stresses set up in wood during seasoning.

Chemical Brown Stain. (See Stain.)

Chipboard. A paperboard used for many purposes that may
or may not have specifications for strength, color, or other
characteristics. It is normally made from paper stock with a
relatively low density in the thickness of 0.1524 mm (0.006
in.) and up.

Cleavage. In an adhesively bonded joint, a separation in the
joint caused by a wedge or other crack-opening-type action.

Close Grained. (See Grain.)

Coarse Grained. (See Grain.)

Cohesion. The state in which the constituents of a mass of
material are held together by chemical and physical forces.

Cold Pressing. A bonding operation in which an assembly
is subjected to pressure without the application of heat.

Collapse. The flattening of single cells or rows of cells in
heartwood during the drying or pressure treatment of wood.
Often characterized by a caved-in or corrugated appearance
of the wood surface.

Compartment Kiln. (See Kiln.)

Composite Assembly. A combination of two or more materials
bonded together that perform as a single unit.

Composite Panel. (See Wood-Based Composite Panel.)

Compound Curvature. Wood bent to a compound curvature,
no element of which is a straight line.

Compreg. Wood in which the cell walls have been impregnated
with synthetic resin and compressed to give it reduced
swelling and shrinking characteristics and increased density
and strength properties.

Compression Failure. Deformation of the wood fibers resulting
from excessive compression along the grain either
in direct end compression or in bending. It may develop in
standing trees due to bending by wind or snow or to internal
longitudinal stresses developed in growth, or it may result
from stresses imposed after the tree is cut. In surfaced lumber,
compression failures may appear as fine wrinkles across
the face of the piece.

Compression Wood. Abnormal wood formed on the lower
side of branches and inclined trunks of softwood trees.
Compression wood is identified by its relatively wide annual
rings (usually eccentric when viewed on cross section
of branch or trunk), relatively large amount of latewood
(sometimes more than 50% of the width of the annual rings
in which it occurs), and its lack of demarcation between
earlywood and latewood in the same annual rings. Compression
wood shrinks excessively longitudinally, compared
with normal wood.

Conditioning (pre and post). The exposure of a material to
the influence of a prescribed atmosphere for a stipulated period
of time or until a stipulated relation is reached between
material and atmosphere.

Conifer. (See Softwoods.)

Connector, Timber. Metal rings, plates, or grids that are
embedded in the wood of adjacent members, as at the bolted
points of a truss, to increase the strength of the joint.

Consistency. That property of a liquid adhesive by virtue of
which it tends to resist deformation. (Consistency is not a
fundamental property but is composed of rheological properties
such as viscosity, plasticity, and other phenomena.)

Construction Adhesive. (See Adhesive.)

Contact Angle. The angle between a substrate plane and the
free surface of a liquid droplet at the line of contact with the

Cooperage. Containers consisting of two round heads and a
body composed of staves held together with hoops, such as
barrels and kegs.

Slack Cooperage—Cooperage used as containers for
dry, semidry, or solid products. The staves are usually
not closely fitted and are held together with beaded steel,
wire, or wood hoops.

Tight Cooperage—Cooperage used as containers for
liquids, semisolids, or heavy solids. Staves are well fitted
and held tightly with cooperage-grade steel hoops.

Copolymer. Substance obtained when two or more types of
monomers polymerize.

Corbel. A projection from the face of a wall or column supporting
a weight.

Core Stock. A solid or discontinuous center ply used in panel-type
glued structures (such as furniture panels and solid
or hollowcore doors).

Coupling Agent. A molecule with different or like functional
groups that is capable of reacting with surface molecules
of two different substances, thereby chemically bridging the

Covalent Bond. A chemical bond that results when electrons
are shared by two atomic nuclei.

Creep. (1) Time-dependent deformation of a wood member
under sustained wood. (2) In an adhesive, the time-dependent
increase in strain resulting from a sustained stress.

Crook. The distortion of lumber in which there is a deviation,
in a direction perpendicular to the edge, from a straight
line from end-to-end of the piece.

Crossband. To place the grain of layers of wood at right
angles in order to minimize shrinking and swelling; also,
in plywood of three or more plies, a layer of veneer whose
grain direction is at right angles to that of the face plies.

Cross Break. A separation of the wood cells across the
grain. Such breaks may be due to internal stress resulting
from unequal longitudinal shrinkage or to external forces.

Cross Grained. (See Grain.)

Cross-Link. An atom or group connecting adjacent molecules
in a complex molecular structure.

Cup. A distortion of a board in which there is a deviation
flatwise from a straight line across the width of the board.

Cure. To change the properties of an adhesive by chemical
reaction (which may be condensation, polymerization,
or vulcanization) and thereby develop maximum strength.
Generally accomplished by the action of heat or a catalyst,
with or without pressure.

Curing Agent. (See Hardener.)

Curing Temperature. (See Temperature, Curing.)

Curing Time. (See Time, Curing.)

Curly Grained. (See Grain.)

Curtain Coating. Applying liquid adhesive to an adherend
by passing the adherend under a thin curtain of liquid falling
by gravity or pressure.

Cut Stock. (See Lumber for Dimension.)

Cuttings. In hardwoods, portions of a board or plank having
the quality required by a specific grade or for a particular
use. Obtained from a board by crosscutting or ripping.

Decay. The decomposition of wood substance by fungi.

Advanced (Typical) Decay—The older stage of decay
in which the destruction is readily recognized because
the wood has become punky, soft and spongy, stringy,
ringshaked, pitted, or crumbly. Decided discoloration or
bleaching of the rotted wood is often apparent.

Brown Rot—In wood, any decay in which the attack concentrates
on the cellulose and associated carbohydrates
rather than on the lignin, producing a light to dark brown
friable residue—hence loosely termed “dry rot.” An advanced
stage where the wood splits along rectangular
planes, in shrinking, is termed “cubical rot.”

Dry Rot—A term loosely applied to any dry, crumbly rot
but especially to that which, when in an advanced stage,
permits the wood to be crushed easily to a dry powder.
The term is actually a misnomer for any decay, since all
fungi require considerable moisture for growth.

Incipient Decay—The early stage of decay that has not
proceeded far enough to soften or otherwise perceptibly
impair the hardness of the wood. It is usually accompanied
by a slight discoloration or bleaching of the wood.

Heart Rot—Any rot characteristically confined to the
heartwood. It generally originates in the living tree.

Pocket Rot—Advanced decay that appears in the form of
a hole or pocket, usually surrounded by apparently sound

Soft Rot—A special type of decay developing under very
wet conditions (as in cooling towers and boat timbers)
in the outer wood layers, caused by cellulose-destroying
microfungi that attack the secondary cell walls and not the
intercellular layer.

White-Rot—In wood, any decay or rot attacking both
the cellulose and the lignin, producing a generally whitish
residue that may be spongy or stringy rot, or occur as
pocket rot.

Delamination. The separation of layers in laminated wood
or plywood because of
failure of the adhesive, either within
the adhesive itself or at the interface between the adhesive
and the adherend.

Delignification. Removal of part or all of the lignin from
wood by chemical treatment.

Density. As usually applied to wood of normal cellular
form, density is the mass per unit volume of wood substance
enclosed within the boundary surfaces of a wood-plus-voids
complex. It is variously expressed as pounds per cubic foot,
kilograms per cubic meter, or grams per cubic centimeter at
a specified moisture content.

Density Rules. A procedure for segregating wood according
to density, based on percentage of latewood and number of
growth rings per inch of radius.

Dew Point. The temperature at which a vapor begins
to deposit as a liquid. Applies especially to water in the

Diagonal Grained. (See Grain.)

Diffuse-Porous Wood. Certain hardwoods in which the
pores tend to be uniform in size and distribution throughout
each annual ring or to decrease in size slightly and gradually
toward the outer border of the ring.

Dimension. (See Lumber for Dimension.)

Dipole–Dipole Forces. Intermolecular attraction forces
between polar molecules that result when positive and negative
poles of molecules are attracted to one another.

Dote. “Dote,” “doze,” and “rot” are synonymous with “decay”
and are any form of decay that may be evident as either
a discoloration or a softening of the wood.

Double Spread. (See Spread.)

Dry-Bulb Temperature. The temperature of air as indicated
by a standard thermometer. (See Psychrometer.)

Dry Kiln. (See Kiln.)

Dry Rot. (See Decay.)

Dry Strength. The strength of an adhesive joint determined
immediately after drying under specified conditions
or after a period of conditioning in a standard laboratory

Drywall. Panel product used as an interior wall and ceiling
covering made of gypsum plaster with paper facings. The
gypsum plaster may be reinforced with recycled fiber.

Durability. A general term for permanence or resistance to
deterioration. Frequently used to refer to the degree of resistance
of a species of wood to attack by wood-destroying
fungi under conditions that favor such attack. In this connection,
the term “decay resistance” is more specific. As
applied to bondlines, the life expectancy of the structural
qualities of the adhesive under the anticipated service conditions
of the structure.

Earlywood. The portion of the growth ring that is formed
during the early part of the growing season. It is usually less
dense and weaker mechanically than latewood.

Edge Grained. (See Grain.)

Edge Joint. (See Joint.)

Elastomer. A macromolecular material that, at room temperature,
is deformed by application of a relatively low force and is capable of recovering
substantially in size and shape after removal of the force.

Embrittlement. A loss in strength or energy absorption
without a corresponding loss in stiffness. Clear, straight-
grained wood is generally considered a ductile material;
chemical treatments and elevated temperatures can alter the
original chemical composition of wood, thereby embrittling
the wood.

Encased Knot. (See Knot.)

End Grained. (See Grain.)

End Joint. (See Joint.)

Equilibrium Moisture Content. The moisture content at
which wood neither

gains nor loses moisture when surrounded
by air at a given relative humidity and temperature.

Excelsior. (See Wood Wool.)

Extender. A substance, generally having some adhesive action,
added to an adhesive to reduce the amount of the primary
binder required per unit area.

Exterior Plywood. (See Wood-Based Composite Panel.)

Extractive. Substances in wood, not an integral part of the
cellular structure, that can be removed by solution in hot or
cold water, ether, benzene, or other solvents that do not react
chemically with wood components.

Extrusion Spreading. A method of adhesive application
in which adhesive is forced through small openings in the
spreader head.

Factory and Shop Lumber. (See Lumber.)

Failure, Adherend. Rupture of an adhesive joint, such that
the separation appears to be within the adherend.

Failure, Adhesive. Rupture of an adhesive joint, such that
the plane of separation appears to be at the adhesive–adherend

Failure, Cohesive. Rupture of an adhesive joint, such that
the separation appears to be within the adhesive.

Feed Rate. The distance that the stock being processed
moves during a given interval of time or operational cycle.

Fiber, Wood. A wood cell comparatively long (=40 to 300
mm, =1.5 to 12 in.), narrow, tapering, and closed at both

Fiberboard. (See Wood-Based Composite Panel.)

Fiber Saturation Point. The stage in the drying or wetting
of wood at which the cell walls are saturated and the
cell cavities free from water. It applies to an individual cell
or group of cells, not to whole boards. It is usually taken
as approximately 30% moisture content, based on ovendry

Fibril. A threadlike component of cell walls, invisible under
a light microscope.

Figure. The pattern produced in a wood surface by annual
growth rings, rays, knots, deviations from regular grain such
as interlocked and wavy grain, and irregular coloration.

Filler. In woodworking, any substance used to fill the holes
and irregularities in planed or sanded surfaces to decrease
the porosity of the surface before applying finish coatings.
As applied to adhesives, a relatively nonadhesive substance
added to an adhesive to improve its working properties,
strength, or other qualities.

Fine Grained. (See Grain.)

Fingerjoint. (See Joint.)

Finish (Finishing). (1) Wood products such as doors, stairs,
and other fine work required to complete a building, especially
the interior. (2) Coatings of paint, varnish, lacquer,
wax, or other similar materials applied to wood surfaces to
protect and enhance their durability or appearance.

Fire Endurance. A measure of the time during which a material
or assembly continues to exhibit fire resistance under
specified conditions of test and performance.

Fire Resistance. The property of a material or assembly
to withstand fire or give protection from it. As applied to
elements of buildings, it is characterized by the ability to
confine a fire or to continue to perform a given structural
function, or both.

Fire Retardant. (See Flame Retardant.)

Fire-Retardant-Treated Wood. As specified in building
codes, a wood product that has been treated with chemicals
by a pressure process or treated during the manufacturing
process for the purpose of reducing its flame spread performance
in an ASTM E 84 test conducted for 30 min to performance
levels specified in the codes.

Flake. A small flat wood particle of predetermined dimensions,
uniform thickness, with fiber direction essentially
in the plane of the flake; in overall character resembling a
small piece of veneer. Produced by special equipment for
use in the manufacture of flakeboard.

Flakeboard. (See Wood-Based Composite Panel.)

Flame Retardant. A treatment, coating, or chemicals that
when applied to wood products delays ignition and reduces
the flame spread of the product.

Flame Spread. The propagation of a flame away from the
source of ignition across the surface of a liquid or a solid, or
through the volume of a gaseous mixture.

Flat Grained. (See Grain.)

Flat Sawn. (See Grain.)

Flecks. (See Rays, Wood.)

Flitch. A portion of a log sawn on two or more faces—commonly
on opposite faces leaving two waney edges. When
intended for resawing into lumber, it is resawn parallel to its
original wide faces. Or, it may be sliced or sawn into veneer,
in which case the resulting sheets of veneer laid together
in the sequence of cutting are called a flitch. The term is
loosely used. (See Cant.)

Framing. Lumber used for the structural member of a
building, such as studs and joists.

Full-Cell Process. Any process for impregnating wood with
preservatives or chemicals in which a vacuum is drawn to
remove air from the wood before admitting the preservative.
This favors heavy adsorption and retention of preservative
in the treated portions.

Furnish. Wood material that has been reduced for incorporation
into conventional wood-based composites; including
flakes, particles, and fiber.

Gelatinous Fibers. Modified fibers that are associated with
tension wood in hardwoods.

Girder. A large or principal beam used to support concentrated
loads at isolated points along its length.

Gluability. (See Bondability.)

Glue. Originally, a hard gelatin obtained from hides,
tendons, cartilage, bones, etc., of animals. Also, an adhesive
prepared from this substance by heating with water.
Through general use, the term is now synonymous with the
term “adhesive.”

Glue Laminating. Production of structural or nonstructural
wood members by bonding two or more layers of wood together
with adhesive.

Glued Laminated Timber (Glulam). A manufactured
structural timber product composed of layers of dimensional
lumber glued together.

Glueline. (See Bondline.)

Grade. The designation of the quality of a manufactured
piece of wood or of logs.

Grain. The direction, size, arrangement, appearance, or
quality of the fibers in wood or lumber. To have a specific
meaning the term must be qualified.

Close-Grained (Fine-Grained) Wood—Wood with narrow,
inconspicuous annual rings. The term is sometimes
used to designate wood having small and closely spaced
pores, but in this sense the term “fine textured” is more
often used.

Coarse-Grained Wood—Wood with wide conspicuous
annual rings in which there is considerable difference
between earlywood and latewood. The term is sometimes
used to designate wood with large pores, such as oak,
keruing, meranti, and walnut, but in this sense, the term
“open-grained” is more often used.

Cross-Grained Wood—Wood in which the fibers deviate
from a line parallel to the sides of the piece. Cross grain
may be either diagonal or spiral grain or a combination of
the two.

Curly-Grained Wood—Wood in which the fibers are distorted
so that they have a curled appearance, as in “birdseye”
wood. The areas showing curly grain may vary up to
several inches in diameter.

Diagonal-Grained Wood—Wood in which the annual
rings are at an angle with the axis of a piece as a result of
sawing at an angle with the bark of the tree or log. A form
of cross-grain.

Edge-Grained Lumber—Lumber that has been sawed
so that the wide surfaces extend approximately at right
angles to the annual growth rings. Lumber is considered
edge grained when the rings form an angle of 45° to 90°
with the wide surface of the piece.

End-Grained Wood—The grain as seen on a cut made
at a right angle to the direction of the fibers (such as on a
cross section of a tree).

Fiddleback-Grained Wood—Figure produced by a
type of fine wavy grain found, for example, in species of
maple; such wood being traditionally used for the backs
of violins.

Flat-Grained (Flat-Sawn) Lumber—Lumber that has
been sawn parallel to the pith and approximately tangent
to the growth rings. Lumber is considered flat grained
when the annual growth rings make an angle of less than
45° with the surface of the piece.

Interlocked-Grained Wood—Grain in which the fibers
put on for several years may slope in a right-handed direction,
and then for a number of years the slope reverses
to a left-handed direction, and later changes back to a
right-handed pitch, and so on. Such wood is exceedingly
difficult to split radially, though tangentially it may split
fairly easily.

Open-Grained Wood—Common classification for
woods with large pores such as oak, keruing, meranti, and
walnut. Also known as “coarse textured.”

Plainsawn Lumber—Another term for flat-grained

Quartersawn Lumber—Another term for edge-grained

Side-Grained Wood—Another term for flat-grained

Slash-Grained Wood—Another term for flat-grained

Spiral-Grained Wood—Wood in which the fibers
take a spiral course about the trunk of a tree instead of
the normal vertical course. The spiral may extend in a
right-handed or left-handed direction around the tree
trunk. Spiral grain is a form of cross grain.

Straight-Grained Wood—Wood in which the fibers run
parallel to the axis of a piece.

Vertical-Grained Lumber—Another term for
edge-grained lumber.

Wavy-Grained Wood—Wood in which the fibers collectively
take the form of waves or undulations.

Green. Freshly sawed or undried wood. Wood that has become
completely wet after immersion in water would not
be considered green but may be said to be in the “green

Growth Ring. The layer of wood growth put on a tree during
a single growing season. In the temperate zone, the annual
growth rings of many species (for example, oaks and
pines) are readily distinguished because of differences in the
cells formed during the early and late parts of the season.
In some temperate zone species (black gum and sweetgum)
and many tropical species, annual growth rings are not easily

Gum. A comprehensive term for nonvolatile viscous plant
exudates, which either dissolve or swell up in contact with
water. Many substances referred to as gums such as pine and
spruce gum are actually oleoresins.

Hardboard. (See Wood-Based Composite Panel.)

Hardener. A substance or mixture of substances that is part
of an adhesive and is used to promote curing by taking part
in the reaction.

Hardness. A property of wood that enables it to resist

Hardwoods. Generally one of the botanical groups of trees
that have vessels or pores and broad leaves, in contrast to
the conifers or softwoods. The term has no reference to the
actual hardness of the wood.

Heart Rot. (See Decay.)

Heartwood. The wood extending from the pith to the sapwood,
the cells of which no longer participate in the life
processes of the tree. Heartwood may contain phenolic compounds,
gums, resins, and other materials that usually make
it darker and more decay resistant than sapwood.

Hemicellulose. A celluloselike material (in wood) that is
easily decomposable as by dilute acid, yielding several different
simple sugars.

Hertz. A unit of frequency equal to one cycle per second.

High Frequency Curing. (See Radiofrequency Curing.)

Hollow-Core Construction. A panel construction with
faces of plywood, hardboard, or similar material bonded to a
framed-core assembly of wood lattice, paperboard rings, or
the like, which support the facing at spaced intervals.

Honeycomb Core. A sandwich core material constructed of
thin sheet materials or ribbons formed to honeycomb-like

Honeycombing. Checks, often not visible at the surface,
that occur in the interior of a piece of wood, usually along
the wood rays.

Hot-Setting Adhesive. (See Adhesive.)

Hydrogen Bond. An intermolecular attraction force that
results when the hydrogen of one molecule and a pair of
unshared electrons on an electronegative atom of another
molecule are attracted to one another.

Hydrophilic. Having a strong tendency to bind or absorb

Hydrophobic. Having a strong tendency to repel water.

Impreg. Wood in which the cell walls have been impregnated
with synthetic resin so as to reduce materially its swelling
and shrinking. Impreg is not compressed.

Incising. A pretreatment process in which incisions, slits, or
perforations are made in the wood surface to increase penetration
of preservative treatments. Incising is often required
to enhance durability of some difficult-to-treat species, but
incising reduces strength.

Increment Borer. An augerlike instrument with a hollow
bit and an extractor, used to extract thin radial cylinders of
wood from trees to determine age and growth rate. Also
used in wood preservation to determine the depth of penetration
of a preservative.

Inorganic-Bonded Composites. Manufactured wood-based
composites where an inorganic binder, typically gypsum,
Portland-cement, or magnesia-cement, acts as a continuous
matrix and fully encapsulates the wood elements.

Intergrown Knot. (See Knot.)

Interior Plywood. (See Wood-Based Composite Panel.)

Interlocked Grained. (See Grain.)

Interlocking Action. (See Mechanical Adhesion.)

Internal Stresses. Stresses that exist within an adhesive
joint even in the absence of applied external forces.

Interphase. In wood bonding, a region of finite thickness
as a gradient between the bulk adherend and bulk adhesive
in which the adhesive penetrates and alters the adherend’s
properties and in which the presence of the adherend influences
the chemical and/or physical properties of the

Intumesce. To expand with heat to provide a low-density
film; used in reference to certain fire-retardant coatings.

Isotropic. Exhibiting the same properties in all directions.

Joint. The junction of two pieces of wood or veneer.

Adhesive Joint—The location at which two adherends
are held together with a layer of adhesive.

Assembly Joint—Joints between variously shaped parts
or subassemblies such as in wood furniture (as opposed to
joints in plywood and laminates that are all quite similar).

Butt Joint—An end joint formed by abutting the squared
ends of two pieces.

Edge Joint—A joint made by bonding two pieces of
wood together edge to edge, commonly by gluing. The
joints may be made by gluing two squared edges as in a
plain edge joint or by using machined joints of various
kinds, such as tongued-and-grooved joints.

End Joint—A joint made by bonding two pieces of wood
together end to end, commonly by finger or scarf joint.

Fingerjoint—An end joint made up of several meshing
wedges or fingers of wood bonded together with an adhesive.
Fingers are sloped and may be cut parallel to either
the wide or narrow face of the piece.

Lap Joint—A joint made by placing one member partly
over another and bonding the overlapped portions.

Scarf Joint—An end joint formed by joining with adhesive
the ends of two pieces that have been tapered or
beveled to form sloping plane surfaces, usually to a featheredge,
and with the same slope of the plane with respect
to the length in both pieces. In some cases, a step or hook
may be machined into the scarf to facilitate alignment of
the two ends, in which case the plane is discontinuous and
the joint is known as a stepped or hooked scarf joint.

Starved Joint—A glue joint that is poorly bonded because
an insufficient quantity of adhesive remained in the

Sunken Joint—Depression in wood surface at a joint
(usually an edge joint) caused by surfacing material too
soon after bonding. (Inadequate time was allowed for
moisture added with the adhesive to diffuse away from
the joint.)

Joint Efficiency or Factor. The strength of a joint
expressed as a percentage of the strength of clear
straight-grained material.

Joist. One of a series of parallel beams used to support floor
and ceiling loads and supported in turn by larger beams,
girders, or bearing walls.

Kiln. A chamber having controlled air-flow, temperature,
and relative humidity for drying lumber. The temperature is
increased as drying progresses, and the relative humidity is

Kiln Dried. (See Seasoning.)

Knot. That portion of a branch or limb that has been surrounded
by subsequent growth of the stem. The shape of the
knot as it appears on a cut surface depends on the angle of
the cut relative to the long axis of the knot.

Encased Knot—A knot whose rings of annual growth are
not intergrown with those of the surrounding wood.

Intergrown Knot—A knot whose rings of annual growth
are completely intergrown with those of the surrounding

Loose Knot—A knot that is not held firmly in place by
growth or position and that cannot be relied upon to remain
in place.

Pin Knot—A knot that is not more than 12 mm (1/2 in.)
in diameter.

Sound Knot—A knot that is solid across its face, at least
as hard as the surrounding wood, and shows no indication
of decay.

Spike Knot—A knot cut approximately parallel to
its long axis so that the exposed section is definitely

Laminate. A product made by bonding together two or
more layers (laminations) of material or materials.

Laminate, Paper-Based. A multilayered panel made by
compressing sheets of resin-impregnated paper together into
a coherent solid mass.

Laminated Strand Lumber (LSL). (See Structural Composite

Laminated Veneer Lumber (LVL). (See Structural Composite

Lap Joint. (See Joint.)

Latewood. The portion of the growth ring that is formed after
the earlywood formation has ceased. It is usually denser
and stronger mechanically than earlywood.

Latex Paint. A paint containing pigments and a stable water
suspension of synthetic resins (produced by emulsion polymerization)
that forms an opaque film through coalescence
of the resin during water evaporation and subsequent curing.

Lathe Checks. In rotary-cut and sliced veneer, the fractures
or checks that develop along the grain of the veneer as the
knife peels veneer from the log. The knife side of the veneer
where checks occur is called the loose side. The opposite
and log side of the veneer where checking usually does not
occur is called the tight side.

Layup. The process of loosely assembling the adhesive-coated
components of a unit, particularly a panel, to be
pressed or clamped.

Lbs/MSGL. Abbreviation for rate of adhesive application
in pounds of adhesive per 1,000 ft2 of single glueline (bondline).
(See Spread.) When both faces of an adherend are
spread as in some plywood manufacturing processes, the
total weight of adhesive applied may be expressed as Lbs/
MDGL (pounds per 1,000 ft2 double glueline).

Lignin. The second most abundant constituent of wood,
located principally in the secondary wall and the middle
lamella, which is the thin cementing layer between wood
cells. Chemically, it is an irregular polymer of substituted
propylphenol groups, and thus, no simple chemical formula
can be written for it.

London Dispersion Forces. Intermolecular attraction forces
between nonpolar molecules that result when instantaneous
(nonpermanent) dipoles induce matching dipoles in neighboring
molecules. London forces also exist between polar

Longitudinal. Generally, parallel to the direction of the
wood fibers.

Loose Knot. (See Knot.)

Lumber. The product of the saw and planing mill for which
manufacturing is limited to sawing, resawing, passing
lengthwise through a standard planing machine, crosscutting
to length, and matching. Lumber may be made from either
softwood or hardwood (See also Lumber for Dimension.)

Board—Lumber that is less than 38 mm standard (2 in.
nominal) thickness and greater than 38 mm standard (2 in
nominal) width. Boards less than 140 mm standard (6 in.
nominal) width are sometimes called strips.

Dimension—Lumber with a thickness from 38 mm
standard (2 in. nominal) up to but not including 114 mm
standard (5 in. nominal) and a width of greater than 38
mm standard (2 in. nominal).

Dressed Size—The dimensions of lumber after being
surfaced with a planing machine. The dressed size is
usually 1/2 to 3/4 in. less than the nominal or rough size.
A 2- by 4-in. stud, for example, actually measures about
1-1/2 by 3-1/2 in. (standard 38 by 89 mm).

Factory and Shop Lumber—Lumber intended to be cut
up for use in further manufacture. It is graded on the percentage
of the area that will produce a limited number of
cuttings of a specified minimum size and quality.

Matched Lumber—Lumber that is edge dressed and
shaped to make a close tongued-and-grooved joint at the
edges or ends when laid edge to edge or end to end.

Nominal Size—As applied to timber or lumber, the size
by which it is known and sold in the market (often differs
from the actual size).

Patterned Lumber—Lumber that is shaped to a pattern
or to a molded form in addition to being dressed,
matched, or shiplapped, or any combination of these

Rough Lumber—Lumber that has not been dressed
(surfaced) but has been sawed, edged, and trimmed.

Shiplapped Lumber—Lumber that is edge dressed to
make a lapped joint.

Shipping-Dry Lumber—Lumber that is partially dried
to prevent stain and mold in transit.

Shop Lumber—(See Factory and Shop Lumber.)

Side Lumber—A board from the outer portion of the
log—ordinarily one produced when squaring off a log
for a tie or timber.

Structural Lumber—Lumber that is intended for use
where allowable properties are required. The grading of
structural lumber is based on the strength or stiffness of
the piece as related to anticipated uses.

Surfaced Lumber—Lumber that is dressed by running
it through a planer.

Timbers—Lumber that is standard 114 mm (nominal 5
in.) or more in least dimension. Timbers may be used as
beams, stringers, posts, caps, sills, girders, or purlins.

Yard Lumber—A little-used term for lumber of all sizes
and patterns that is intended for general building purposes
having no design property requirements.

Lumber for Dimension. The National Dimension Manufacturers
Association defines both hardwood and softwood
dimension components as being cut to a specific size from

kiln-dried rough lumber, bolts, cants, or logs. Dimension
components include Flat Stock (solid and laminated) for
furniture, cabinet, and specialty manufactures. This term has
largely superceded the terms “hardwood dimension” and
“dimension parts.” (See also Lumber).

Lumen. In wood anatomy, the cell cavity.

Manufacturing Defects. Includes all defects or blemishes
that are produced in manufacturing, such as chipped grain,
loosened grain, raised grain, torn grain, skips in dressing, hit
and miss (series of surfaced areas with skips between them),
variation in sawing, miscut lumber, machine burn, machine
gouge, mismatching, and insufficient tongue or groove.

Mastic. A material with adhesive properties, usually used in
relatively thick sections, that can be readily applied by extrusion,
trowel, or spatula. (See Adhesive.)

Matched Lumber. (See Lumber.)

Mechanical Adhesion. Adhesion between surfaces in which
the adhesive holds the parts together by interlocking action.

Medium-Density Fiberboard. (See Wood-Based Composite

Millwork. Planed and patterned lumber for finish work in
buildings, including items such as sash, doors, cornices,
panelwork, and other items of interior or exterior trim. Does
not include flooring, ceiling, or siding.

Mineral Streak. An olive to greenish-black or brown discoloration
of undetermined cause in hardwoods.

Modified Wood. Wood processed by chemical treatment,
compression, or other means (with or without heat) to impart
properties quite different from those of the original

Moisture Content. The amount of water contained in the
wood, usually expressed as a percentage of the weight of the
ovendry wood.

Molecular Weight. The sum of the atomic weights of the
atoms in a molecule.

Moulding. A wood strip having a curved or projecting surface,
used for decorative purposes.

Monomer. A relatively simple molecular compound that can
react at more than one site to form a polymer

Mortise. A slot cut into a board, plank, or timber, usually
edgewise, to receive the tenon of another board, plank, or
timber to form a joint.

Nanoindentation Hardness. A hardness measurement
conducted at the nanometer scale. Nanoindentation hardness
uses an extremely small indenter of a hard material and
specified shape to press into the surface of a specimen with
sufficient force to cause deformation.

Naval Stores. A term applied to the oils, resins, tars, and
pitches derived from oleoresin contained in, exuded by, or
extracted from trees, chiefly species of pines (genus Pinus).
Historically, these were important items in the stores of
wood sailing vessels.

Nominal-Size Lumber. (See Lumber for Dimension.)

Nonpolar. (See Polar.)

Nonpressure Process. Any process of treating wood with a
preservative or fire retardant where pressure is not applied.
Some examples are surface applications by brushing or brief
dipping, soaking in preservative oils, or steeping in solutions
of waterborne preservatives; diffusion processes with
waterborne preservatives; and vacuum treatments.

Oil Paint. A paint containing a suspension of pigments in
an organic solvent and a drying oil, modified drying oil,
or synthetic polymer that forms an opaque film through a
combination of solvent evaporation and curing of the oil or

Old Growth. Timber in or from a mature, naturally established
forest. When the trees have grown during most if not
all of their individual lives in active competition with their
companions for sunlight and moisture, this timber is usually
straight and relatively free of knots.

Oleoresin. A solution of resin in an essential oil that occurs
in or exudes from many plants, especially softwoods.
The oleoresin from pine is a solution of pine resin (rosin) in

Open Assembly Time. (See Time, Assembly.)

Open Grain. (See Grain.)

Oriented Strandboard. (See Wood-Based Composite

Oriented Strand Lumber (OSL). (See Structural Composite

Orthotropic. Having unique and independent properties in
three mutually orthogonal (perpendicular) planes of symmetry.
A special case of anisotropy.

Ovendry Wood. Wood dried to a relatively constant weight
in a ventilated oven at 102 to 105 °C (215 to 220 °F).

Overlay. A thin layer of paper, plastic, film, metal foil, or
other material bonded to one or both faces of panel products
or to lumber to provide a protective or decorative face or a
base for painting.

Paint. Any pigmented liquid, liquifiable, or mastic composition
designed for application to a substrate in a thin layer
that converts to an opaque solid film after application.

Pallet. A low wood or metal platform on which material can
be stacked to facilitate mechanical handling, moving, and

Paperboard. The distinction between paper and paperboard
is not sharp, but broadly speaking, the thicker (greater than
0.3 mm (0.012 in.)), heavier, and more rigid grades of paper
are called paperboard.

Papreg. Any of various paper products made by impregnating
sheets of specially manufactured high-strength paper
with synthetic resin and laminating the sheets to form a
dense, moisture-resistant product.

Parallel Strand Lumber (PSL). (See Structural Composite

Parenchyma. Short cells having simple pits and functioning
primarily in the metabolism and storage of plant food materials.
They remain alive longer than the tracheids, fibers, and
vessel elements, sometimes for many years. Two kinds of
parenchyma cells are recognized—those in vertical strands,
known more specifically as axial parenchyma, and those in
horizontal series in the rays, known as ray parenchyma.

Particleboard. (See Wood-Based Composite Panel.)

Particles. The aggregate component of particleboard manufactured
by mechanical means from wood. These include
all small subdivisions of wood such as chips, curls, flakes,
sawdust, shavings, slivers, strands, wafers, wood flour, and
wood wool.

Peck. Pockets or areas of disintegrated wood caused by advanced
stages of localized decay in the living tree. It is usually
associated with cypress and incense-cedar. There is no
further development of peck once the lumber is seasoned.

Peel. To convert a log into veneer by rotary cutting. In an
adhesively bonded joint, the progressive separation of a
flexible member from either a rigid member or another flexible

Phloem. The tissues of the inner bark, characterized by
the presence of sieve tubes and serving for the transport of
elaborate foodstuffs.

Pile. A long, heavy timber, round or square, that is driven
deep into the ground to provide a secure foundation for
structures built on soft, wet, or submerged sites (for example,
landing stages, bridge abutments).

Pin Knot. (See Knot.)

Pitch Pocket. An opening extending parallel to the annual
growth rings and containing, or that has contained, pitch,
either solid or liquid.

Pitch Streaks. A well-defined accumulation of pitch in a
more or less regular streak in the wood of certain conifers.

Pith. The small, soft core occurring near the center of a tree
trunk, branch, twig, or log.

Pith Fleck. A narrow streak, resembling pith on the surface
of a piece; usually brownish, up to several centimeters long;
results from burrowing of larvae in the growing tissues of
the tree.

Plainsawn. (See Grain.)

Planing Mill Products. Products worked to pattern, such as
flooring, ceiling, and siding.

Plank. A broad, thick board laid with its wide dimension
horizontal and used as a bearing surface.

Plasticizing Wood. Softening wood by hot water, steam, or
chemical treatment to increase its moldability.

Plywood. (See Wood-Based Composite Panel.)

Pocket Rot. (See Decay.)

Polar. Characteristic of a molecule in which the positive and
negative electrical charges are permanently separated, as opposed
to nonpolar molecules in which the charges coincide.
Water, alcohol, and wood are polar in nature; most hydrocarbon
liquids are not.

Polymerization. A chemical reaction in which the molecules
of a monomer are linked together to form large molecules
whose molecular weight is a multiple of that of the
original substance. When two or more different monomers
are involved, the process is called copolymerization.

Pore. (See Vessel Elements.)

Postformed Plywood. (See Wood-Based Composite

Post Cure. (1) A treatment (normally involving heat) applied
to an adhesive assembly following the initial cure,
to complete cure, or to modify specific properties. (2) To
expose an adhesive assembly to an additional cure, following
the initial cure; to complete cure; or to modify specific

Pot Life. (See Working Life.)

Precure. Condition of too much cure, set, or solvent loss of
the adhesive before pressure is applied, resulting in inadequate
flow, transfer, and bonding.

Preservative. Any substance that, for a reasonable length of
time, is effective in preventing the development and action
of wood-rotting fungi, borers of various kinds, and harmful
insects that deteriorate wood.

Pressure Process. Any process of treating wood in a closed
container whereby the preservative or fire retardant is forced
into the wood under pressures greater than one atmosphere.
Pressure is generally preceded or followed by vacuum, as in
the vacuum-pressure and empty-cell processes respectively;
or they may alternate, as in the full-cell and alternating-pressure

Progressive Kiln. (See Kiln.)

Psychrometer. An instrument for measuring the amount of
water vapor in the atmosphere. It has both a dry-bulb and
wet-bulb thermometer. The bulb of the wet-bulb thermometer
is kept moistened and is, therefore, cooled by evaporation
to a temperature lower than that shown by the dry-bulb
thermometer. Because evaporation is greater in dry air, the
difference between the two thermometer readings will be
greater when the air is dry than when it is moist.

Quartersawn. (See Grain.)

Radial. Coincident with a radius from the axis of the tree
or log to the circumference. A radial section is a lengthwise
section in a plane that passes through the centerline of the
tree trunk.

Radiofrequency (RF) Curing. Curing of bondlines by the
application of radiofrequency energy. (Sometimes called
high-frequency curing.)

Rafter. One of a series of structural members of a roof designed
to support roof loads. The rafters of a flat roof are
sometimes called roof joists.

Raised Grain. A roughened condition of the surface of
dressed lumber in which the hard latewood is raised above
the softer earlywood but not torn loose from it.

Rays, Wood. Strips of cells extending radially within a tree
and varying in height from a few cells in some species to 4
or more inches in oak. The rays serve primarily to store food
and transport it horizontally in the tree. On quartersawn oak,
the rays form a conspicuous figure, sometimes referred to as

Reaction Wood. Wood with more or less distinctive anatomical
characters, formed typically in parts of leaning or
crooked stems and in branches. In hardwoods, this consists
of tension wood, and in softwoods, compression wood.

Relative Humidity. Ratio of the amount of water vapor
present in the air to that which the air would hold at saturation
at the same temperature. It is usually considered on the
basis of the weight of the vapor but, for accuracy, should be
considered on the basis of vapor pressures.

Resilience. The property whereby a strained body gives up
its stored energy on the removal of the deforming force.

Resin. (1) Solid, semisolid, or pseudosolid resin—An organic
material that has an indefinite and often high molecular
weight, exhibits a tendency to flow when subjected to
stress, usually has a softening or melting range, and usually
fractures conchoidally. (2) Liquid resin—an organic polymeric
liquid that, when converted to its final state for use,
becomes a resin.

Resin Ducts. Intercellular passages that contain and transmit
resinous materials. On a cut surface, they are usually
inconspicuous. They may extend vertically parallel to the
axis of the tree or at right angles to the axis and parallel to
the rays.

Retention by Assay. The determination of preservative
retention in a specific zone of treated wood by extraction or
analysis of specified samples.

Rheology. The study of the deformation and flow of matter.

Ring Failure. A separation of the wood during seasoning,
occurring along the grain and parallel to the growth rings.
(See Shake.)

Ring-Porous Woods. A group of hardwoods in which the
pores are comparatively large at the beginning of each annual
ring and decrease in size more or less abruptly toward
the outer portion of the ring, thus forming a distinct inner
zone of pores, known as the earlywood, and an outer zone
with smaller pores, known as the latewood.

Ring Shake. (See Shake.)

Rip. To cut lengthwise, parallel to the grain.

Roll Spreading. Application of a film of a liquid material to
a surface by means of rollers.

Room-Temperature-Setting Adhesive. (See Adhesive.)

Rot. (See Decay.)

Rotary-Cut Veneer. (See Veneer.)

Rough Lumber. (See Lumber.)

Sap Stain. (See Stain.)

Sapwood. The wood of pale color near the outside of the
log. Under most conditions, the sapwood is more susceptible
to decay than heartwood.

Sash. A frame structure, normally glazed (such as a window),
that is hung or fixed in a frame set in an opening.

Sawn Veneer. (See Veneer.)

Saw Kerf. (1) Grooves or notches made in cutting with a
saw. (2) That portion of a log, timber, or other piece of wood
removed by the saw in parting the material into two pieces.

Scarf Joint. (See Joint.)

Schedule, Kiln Drying. A prescribed series of dry- and
wet-bulb temperatures and air velocities used in drying a
kiln charge of lumber or other wood products.

Seasoning. Removing moisture from green wood to improve
its serviceability.

Air Dried—Dried by exposure to air in a yard or shed,
without artificial heat.

Kiln Dried—Dried in a kiln with the use of artificial heat.

Second Growth. Timber that has grown after the removal,
whether by cutting, fire, wind, or other agency, of all or a
large part of the previous stand.

Semitransparent Stain. A suspension of pigments in either
a drying oil–organic solvent mixture or a water–polymer
emulsion, designed to color and protect wood surfaces by
penetration without forming a surface film and without hiding
wood grain.

Set. A permanent or semipermanent deformation. In reference
to adhesives, to convert an adhesive into a fixed or
hardened state by chemical or physical action, such as condensation,
polymerization, oxidation, vulcanization, gelation,
hydration, or evaporation of volatile constituents.

Shake. A separation along the grain, the greater part of
which occurs between the rings of annual growth. Usually
considered to have occurred in the standing tree or during

Shakes. In construction, shakes are a type of shingle
usually hand cleft from a bolt and used for roofing or

Shaving. A small wood particle of indefinite dimensions
developed incidental to certain woodworking operations
involving rotary cutterheads usually turning in the direction
of the grain. This cutting action produces a thin chip of
varying thickness, usually feathered along at least one edge
and thick at another and generally curled.

Shear. In an adhesively bonded joint, stress, strain, or failure
resulting from applied forces that tends to cause adjacent
planes of a body to slide parallel in opposite directions.

Sheathing. The structural covering, usually of boards,
building fiberboards, plywood, or oriented strandboard,
placed over exterior studding or rafters of a structure.

Shelf Life. (See Storage Life.)

Shiplapped Lumber. (See Lumber.)

Shipping-Dry Lumber. (See Lumber.)

Shop Lumber. (See Lumber.)

Side Grained. (See Grain.)

Side Lumber. (See Lumber.)

Siding. The finish covering of the outside wall of a frame
building, whether made of horizontal weatherboards, vertical
boards with battens, shingles, or other material.

Slash Grained. (See Grain.)

Sliced Veneer. (See Veneer.)

Soft Rot. (See Decay.)

Softwoods. Generally, one of the botanical groups of trees
that have no vessels and in most cases have needlelike or
scalelike leaves, the conifers, also the wood produced by
such trees. The term has no reference to the actual hardness
of the wood.

Solid Color Stains (Opaque Stains). A suspension of pigments
in either a drying oil–organic solvent mixture or a water–
polymer emulsion designed to color and protect a wood
surface by forming a film. Solid color stains are similar to
paints in application techniques and in performance.

Solids Content. The percentage of weight of the nonvolatile
matter in an adhesive.

Solvent Adhesive. (See Adhesive.)

Sound Knot. (See Knot.)

Specific Adhesion. Adhesion between surfaces that are held
together by valence forces of the same type as those that
give rise to cohesion.

Specific Gravity. As applied to wood, the ratio of the ovendry
weight of a sample to the weight of a volume of water
equal to the volume of the sample at a specified moisture
content (green, air dry, or ovendry).

Spike Knot. (See Knot.)

Spiral Grained. (See Grain.)

Spread. The quantity of adhesive per unit joint area applied
to an adherend. (See Lbs/MSGL.)

Single spread—Refers to application of adhesive to only
one adherend of a joint.

Double spread—Refers to application of adhesive to
both adherends of a joint.

Squeezeout. Bead of adhesive squeezed out of a joint when
pressure is applied.

Stain. A discoloration in wood that may be caused by such
diverse agencies as micro-organisms, metal, or chemicals.
The term also applies to materials used to impart color to

Blue Stain—A bluish or grayish discoloration of the
sapwood caused by the growth of certain dark-colored
fungi on the surface and in the interior of the wood; made
possible by the same conditions that favor the growth of
other fungi.

Brown Stain—A rich brown to deep chocolate-brown
discoloration of the sapwood of some pines caused by a
fungus that acts much like the blue-stain fungi.

Chemical Brown Stain—A chemical discoloration of
wood, which sometimes occurs during the air drying or
kiln drying of several species, apparently caused by the
concentration and modification of extractives.

Sap Stain—A discoloration of the sapwood caused by the
growth of certain fungi on the surface and in the interior
of the wood; made possible by the same conditions that
favor the growth of other fungi.

Sticker Stain—A brown or blue stain that develops in
seasoning lumber where it has been in contact with the

Starved Joint. (See Joint.)

Static Bending. Bending under a constant or slowly applied
load; flexure.

Staypak. Wood that is compressed in its natural state (that
is, without resin or other chemical treatment) under controlled
conditions of moisture, temperature, and pressure
that practically eliminate springback or recovery from compression.
The product has increased density and strength

Stickers. Strips or boards used to separate the layers of lumber
in a pile and thus improve air circulation.

Sticker Stain. (See Stain.)

Storage Life. The period of time during which a packaged
adhesive can be stored under specific temperature conditions
and remain suitable for use. Sometimes called shelf life.

Straight Grained. (See Grain.)

Strand. (1) A type of wood flake with a high aspect ratio
which allows for orientation. It is used in oriented strandboard,
oriented strand lumber, and laminated strand lumber.
(2) A wood element with a high aspect ratio manufactured
from veneer. It is used in parallel strand lumber.

Strength. (1) The ability of a member to sustain stress
without failure. (2) In a specific mode of test, the maximum
stress sustained by a member loaded to failure.

Strength Ratio. The hypothetical ratio of the strength of
a structural member to that which it would have if it contained
no strength-reducing characteristics (such as knots,
slope-of-grain, shake).

Stress-Wave Timing. A method of measuring the apparent
stiffness of a material by measuring the speed of an induced
compression stress as it propagates through the material.

Stressed-Skin Construction. A construction in which panels
are separated from one another by a central partition of
spaced strips with the whole assembly bonded so that it acts
as a unit when loaded.

Stringer. A timber or other support for cross members in
floors or ceilings. In stairs, the support on which the stair
treads rest.

Structural Composite Lumber (SCL). (Wood elements
glued together to form products that are similar in size to
solid-sawn lumber)

Laminated Strand Lumber (LSL)—Similar to oriented
strand lumber with somewhat longer strands.

Laminated Veneer Lumber (LVL)—Structural composite
lumber manufactured from veneers laminated
into a panel with the grain of all veneer running parallel
to each other. The resulting panel is ripped to common
lumber dimensions.

Oriented Strand Lumber (OSL)—Structural composite
lumber made from wood strand elements similar
to those used in oriented strand board. The strands are
oriented primarily along the length of the member.

Parallel Strand Lumber (PSL)—Structural composite
lumber made from high aspect ratio wood strand elements
manufactured from veneer oriented primarily
along the length of the member. It is manufactured in
billets and cut to lumber dimensions.

Structural Lumber. (See Lumber.)

Structural Timbers. Pieces of wood of relatively large size,
the strength or stiffness of which is the controlling element
in their selection and use. Examples of structural timbers are
trestle timbers (stringers, caps, posts, sills, bracing, bridge
ties, guardrails); car timbers (car framing, including upper
framing, car sills); framing for building (posts, sills, girders);
ship timber (ship timbers, ship decking); and crossarms
for poles.

Stud. One of a series of slender wood structural members
used as supporting elements in walls and partitions.

Substrate. A material upon the surface of which an adhesive-containing
substance is spread for any purpose, such
as bonding or coating. A broader term than adherend. (See

Surface Inactivation. In adhesive bonding to wood, physical
and chemical modifications of the wood surface that result
in reduced ability of an adhesive to properly wet, flow,
penetrate, and cure.

Surface Tension. The force per unit length acting in the
surface of a liquid that opposes the increase in area of the
liquid (spreading).

Surfaced Lumber. (See Lumber.)

Symmetrical Construction. Panels in which the plies on
one side of a center ply or core are essentially equal in thickness,
grain direction, properties, and arrangement to those
on the other side of the core.

Tack. The property of an adhesive that enables it to form a
bond of measurable strength immediately after adhesive and
adherend are brought into contact under low pressure.

Tangential. Strictly, coincident with a tangent at the circumference
of a tree or log, or parallel to such a tangent. In
practice, however, it often means roughly coincident with
a growth ring. A tangential section is a longitudinal section
through a tree or limb perpendicular to a radius. Flat-grained
lumber is sawed tangentially.

Temperature, Curing. The temperature to which an adhesive
or an assembly is subjected to cure the adhesive. The temperature
attained by the adhesive in the process of curing
(adhesive curing temperature) may differ from the temperature
of the atmosphere surrounding the assembly (assembly
curing temperature).

Temperature, Setting. (See Temperature, Curing.)

Tenon. A projecting member left by cutting away the wood
around it for insertion into a mortise to make a joint.

Tension. In an adhesively bonded joint, a uniaxial force
tending to cause extension of the assembly, or the counteracting
force within the assembly that resists extension.

Tension Wood. Abnormal wood found in leaning trees of
some hardwood species and characterized by the presence
of gelatinous fibers and excessive longitudinal shrinkage.
Tension wood fibers hold together tenaciously, so that sawed
surfaces usually have projecting fibers and planed surfaces
often are torn or have raised grain. Tension wood may cause

Texture. A term often used interchangeably with grain.
Sometimes used to combine the concepts of density and
degree of contrast between earlywood and latewood. In
this handbook, texture refers to the finer structure of the
woodrather than the annual rings. (See also Grain.)

Thermoplastic. (1) Capable of being repeatedly softened
by heat and hardened by cooling. (2) A material that will
repeatedly soften when heated and harden when cooled.

Thermoset. A cross-linked polymeric material.

Thermosetting. Having the property of undergoing a chemical
reaction by the action of heat, catalyst, ultraviolet light,
and hardener, leading to a relatively infusible state.

Timbers, Round. Timbers used in the original round form,
such as poles, piling, posts, and mine timbers.

Timber, Standing. Timber still on the stump.

Timbers. (See Lumber.)

Time, Assembly. The time interval between the spreading
of the adhesive on the adherend and the application of
pressure or heat, or both, to the assembly. (For assemblies
involving multiple layers or parts, the assembly time begins
with the spreading of the adhesive on the first adherend.)

Open Assembly Time—The time interval between the
spreading of the adhesive on the adherend and the completion
of assembly of the parts for bonding.

Closed Assembly Time—The time interval between
completion of assembly of the parts for bonding and the
application of pressure or heat, or both, to the assembly.

Time, Curing. The period during which an assembly is subjected
to heat or pressure, or both, to cure the adhesive.

Time, Setting. (See Time, Curing.)

Toughness. A quality of wood that permits the material to
absorb a relatively large amount of energy, to withstand
repeated shocks, and to undergo considerable deformation
before breaking.

Tracheid. The elongated cells that constitute the greater part
of the structure of the softwoods (frequently referred to as
fibers). Also present in some hardwoods.

Transfer. In wood bonding, the sharing of adhesive between
a spread and an unspread surface when the two adherends
are brought into contact.

Transverse. Directions in wood at right angles to the wood
fibers. Includes radial and tangential directions. A transverse
section is a section through a tree or timber at right angles to
the pith.

Treenail. A wooden pin, peg, or spike used chiefly for fastening
planking and ceiling to a framework.

Trim. The finish materials in a building, such as moldings,
applied around openings (window trim, door trim) or at the
floor and ceiling of rooms (baseboard, cornice, and other

Truss. An assembly of members, such as beams, bars, rods,
and the like, so combined as to form a rigid framework. All
members are interconnected to form triangles.

Twist. A distortion caused by the turning or winding of the
edges of a board so that the four comers of any face are no
longer in the same plane.

Tyloses. Masses of parenchyma cells appearing somewhat
like froth in the pores of some hardwoods, notably the white
oaks and black locust. Tyloses are formed by the extension
of the cell wall of the living cells surrounding vessels of

Ultrasonics. (See Stress-Wave Timing.)

van der Waal Forces. Physical forces of attraction between
molecules, which include permanent dipole, induced dipole,
hydrogen bond, and London dispersion forces.

Vapor Retarder. A material with a high resistance to vapor
movement, such as foil, plastic film, or specially coated
paper, that is used in combination with insulation to control

Veneer. A thin layer or sheet of wood.

Rotary-Cut Veneer—Veneer cut in a lathe that rotates a
log or bolt, chucked in the center, against a knife.

Sawn Veneer—Veneer produced by sawing.

Sliced Veneer—Veneer that is sliced off a log, bolt, or
flitch with a knife.

Vertical Grained. (See Grain.)

Vessel Elements. Wood cells in hardwoods of comparatively
large diameter that have open ends and are set one
above the other to form continuous tubes called vessels. The
openings of the vessels on the surface of a piece of wood are
usually referred to as pores.

Virgin Growth. The growth of mature trees in the original

Viscoelasticity. The ability of a material to simultaneously
exhibit viscous and elastic responses to deformation.

Viscosity. The ratio of the shear stress existing between
laminae of moving fluid and the rate of shear between these

Wane. Bark or lack of wood from any cause on edge or corner
of a piece except for eased edges.

Warp. Any variation from a true or plane surface. Warp
includes bow, crook, cup, and twist, or any combination

Water Repellent. A liquid that penetrates wood that materially
retards changes in moisture content and dimensions
of the dried wood without adversely altering its desirable

Water-Repellent Preservative. A water repellent that contains
a preservative that, after application to wood and drying,
accomplishes the dual purpose of imparting resistance
to attack by fungi or insects and also retards changes in
moisture content.

Weathering. The mechanical or chemical disintegration and
discoloration of the surface of wood caused by exposure
to light, the action of dust and sand carried by winds, and
the alternate shrinking and swelling of the surface fibers
with the continual variation in moisture content brought by
changes in the weather. Weathering does not include decay.

Wet Strength. The strength of an adhesive joint determined
immediately after removal from water in which it has been
immersed under specified conditions of time, temperature,
and pressure.

Wet-Bulb Temperature. The temperature indicated by the
wet-bulb thermometer of a psychrometer.

Wettability. A condition of a surface that determines how
fast a liquid will wet and spread on the surface or if it will
be repelled and not spread on the surface.

Wetting. The process in which a liquid spontaneously adheres
to and spreads on a solid surface.

White-Rot. (See Decay.)

Wood-Based Composite Panel. A generic term for a material
manufactured from wood veneer, strands, flakes,
particles, or fibers or other lignocellulosic material and a
synthetic resin or other binder.

Cellulosic Fiberboard—A generic term for a low-density
panel made from lignocellulosic fibers characterized by
an integral bond produced by interfelting of the fibers, to
which other materials may have been added during manufacture
to improve certain properties, but which has not
been consolidated under heat and pressure as a separate
stage in manufacture; has a density of less than 496 kg
m–3 (31 lb ft–3) (specific gravity 0.50 ) but more than 160
kg m–3 (10 lb ft–3) (specific gravity 0.16).

Exterior Plywood—A general term for plywood bonded
with a type of adhesive that by systematic tests and service
records has proved highly resistant to weather; microorganisms;
cold, hot, and boiling water; steam; and dry

Fiberboard—A generic term inclusive of panel products
of various densities manufactured of refined or partially
refined wood (or other lignocellulosic) fibers. Bonding
agents may be added.

Flakeboard—A generic term indicating a manufactured
panel product composed of flakes bonded with a synthetic

Hardboard—A generic term for a panel manufactured
primarily from interfelted lignocellulosic fibers (usually
wood), consolidated under heat and pressure in a hot press
to a density of 496 kg m–33 (31 lb ft–3) or greater. May be
manufactured using either a dry-process or wet-process.

Interior Plywood—A general term for plywood manufactured
for indoor use or in construction subjected to
only temporary moisture. The adhesive used may be interior,
intermediate, or exterior.

Medium-Density Fiberboard—A dry-process fiberboard
manufactured from lignocellulosic fibers combined with
a synthetic resin or other suitable binder. The panels are
manufactured to a density of 496 kg m–3 (31 lb ft–3) (0.50
specific gravity) to 880 kg m–3 (55 lb ft–3) (0.88 specific
gravity) by the application of heat and pressure by a process
in which the interfiber bond is substantially created
by the added binder.

Oriented Strandboard—A type of flakeboard product
composed of strand-type flakes that are purposefully
aligned in directions that make a panel stronger,
stiffer, and with improved dimensional properties in the
alignment directions than a panel with random flake

Particleboard—A panel product manufactured from
wood particles usually in three layers. For good surface
characteristics, the outer layers have smaller particles and
the interior uses coarser particles. The particles in the core
may or may not be aligned.

Plywood—A glued wood panel made up of relatively thin
layers of veneer with the grain of adjacent layers at right
angles or of veneer in combination with a core of lumber
or of reconstituted wood. The usual constructions have an
odd number of layers.

Wood Failure. The rupturing of wood fibers in strength
tests of bonded joints usually expressed as the percentage of
the total area involved that shows such failure. (See Failure,

Wood Flour. Wood reduced to finely divided particles, approximately
the same as those of cereal flours in size, appearance,
and texture, and passing a 40 to 100 mesh screen.

Wood Substance. The solid material of which wood is
composed. It usually refers to the extractive-free solid
substance of which the cell walls are composed, but this is
not always true. There is not a wide variation in chemical
composition or specific gravity between the wood substance
of various species. (The characteristic differences of species
are largely due to differences in extractives and variations in
relative amounts of cell walls and cell cavities.)

Wood-Thermoplastic Composite. Manufactured composite
materials consisting primarily of wood elements and
thermoplastic. The wood element may either serve as a reinforcement
or filler in a continuous thermoplastic matrix, or
the thermoplastic may act as a binder to the wood element.

Wood Wool. Long, curly, slender strands of wood used
as an aggregate component for some particleboards and
cement-bonded composites. Sometimes referred to as

Workability. The degree of ease and smoothness of cut obtainable
with hand or machine tools.

Working Life. The period of time during which an adhesive,
after mixing with catalyst, solvent, or other compounding
ingredients, remains suitable for use. Also called pot life.

Working Properties. The properties of an adhesive that
affect or dictate the manner of application to the adherends
to be bonded and the assembly of the joint before pressure
application (such as viscosity, pot life, assembly time, setting

Xylem. The portion of the tree trunk, branches, and roots
that lies between the pith and the cambium (that is the

Yard Lumber. (See Lumber.)