Glossary of Terms – Hardwood Flooring – “G” Through “R”

Gloss The amount of shine on a finished board or reflecting ability of surface.
An instrument for measuring the luster or gloss of a finished surface.
Glossing Up   The increase of luster in a rubbed film through friction in use or the increase
in luster of a flat varnish in the package through a decrease in the effect of a flattening agent.
 A groove or cavity in the flooring surface accompanied by material removal and penetration
below the immediate flooring surface.
Grade The designation of the quality of a manufactured piece of wood or of logs.
Specifications or guides for classifying wood or manufactured pieces according to quality or use.
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.

Edge Grain – (Quarter Sawn)  Wood that has been sawed so that the wide surfaces extend
approximately at right angles to the annual growth rings.  Wood is considered edge grained
when the rings form an angle of 45 degrees to 90 degrees with the wide surface of the piece.
See Vertical Grain.

Flat Grain – (Flat Sawn, Plain Grain, Plain Sawed, Slash Grain, Tangential Cut) Wood products
sawed parallel to the pith and approximately tangent to the growth rings. Wood is considered
flat grained when the annual growth rings make an angle of less than 45 degrees with the
surface of the piece.

Open Grain – Common classification for woods with large pores, such as oak, ash, chestnut
and walnut. Also known as “coarse textured”.

Torn Grain – Wood products in which fibers are torn out below the finished surface, particularly
around knots and curly places, by the action of planer knives.

Vertical Grain – Wood that has been sawed so that the wide surfaces extend approximately at
right angles to the annual growth rings. Wood is considered edge grained when the rings form an
angle of 45 degrees to 90 degrees with the wide surface of the piece.
The appearance of small, grain-like particles in a finishing or in the dried film thereof.
Grub Worm
Grub worm holes can be up to a 1/2″ in diameter.
Hardness   That property of the wood species or dried film of finishing material that causes it to withstand
denting or being marked when pressure is exerted on its surface by an outside object or force.
Generally one of the botanical groups of trees that have broad leaves in contrast to the conifers
or softwood.The term has no reference to the actual hardness of the wood.
HartWood   The top ply treatment of products that are acrylic impregnated without a top coat.
Heartwood   The inner layer of a woody stem wholly composed of nonliving cells and usually differentiated
from the outer enveloping layer (sapwood) by its darker color.
Heartwood is the support structure for the living tree. It is usually more decay resistant than sapwood.
Spots and streaks of sufficient size and density to severely affect the appearance of the wood.
A general term used to denote the presence of a higher than average percentage of solid ingredients
and thus a lower percentage of solvents.
Holes Openings in or through lumber that may extend partially or entirely through a piece and may be from
any cause.  Holes extending partially through a piece are often termed surface pits. The size of a hole
is the average to its maximum and minimum surface diameters unless otherwise specified.
Hollowback   The grooves, usually two, that run length-wise down the back of flooring.
Honeycombing   In lumber and other wood products separation of the fibers in the interior of the piece, usually along
the wood rays. Honeycombing is often not visible on the surface, although it can be the extensions of
surface and end checks. Generally caused seasoning. (Hollow Horning, Internal Checking, Interior Checking,
Inner Checking).
Humidity The amount of water vapor in the air. See Relative Humidity
Hygrometer   An instrument for measuring the degree of humidity or relative humidity of the atmosphere.
Hygroscopic A substance that can absorb and retain moisture, or lose or throw off moisture. Wood and wood products
are hygroscopic. They expand with absorption of moisture and their dimensions become smaller when
moisture is lost or thrown off.
A test for determining the resistance to shattering of a dried film by dropping a weight onto the finish.
The early stage of decay that has not proceeded far enough to soften or otherwise perceptibly impair
the hardness of the wood.
Intensity The intensity of a color is its purity or degree of hue as seen by the eye.
Strip flooring, generally birch, beech, hard maple or pecan, manufactured with square edges, not
side-matched, but usually end-matched. It is used principally for factory floors where the square edges
make replacement of strips easier.
Joist   One of a series of parallel beams used to support floor or ceiling loads and supported in turn by
larger beams, girders or bearing walls.
The initial wood formed adjacent to the pith, characterized often by lower specific gravity, lower strength,
higher longitudinal shrinkage, and different micro-structure than mature wood. The amount of juvenile
wood may vary from tree-to-tree and may extend from the pith to between 5 to 20 growth rings from
the pith.
A chamber or tunnel used for drying and conditioning lumber, veneer, and other wood products in which
the temperature and relative humidity of the circulated air can be varied and controlled, often steam heated
and vented.
Charge – In kiln drying, the total amount of lumber or wood items to be  dried in a dry kiln.

Dried – Lumber or other wood items that were dried in a closed chamber in which temperature and
relative humidity of the circulated air can be controlled.
Kinks Kinks are an abrupt offset in the edge surface that usually occurs near the ends of the piece.
A series of surface imprints or markings made by the machine knives in dressed lumber.
Knot That portion of a branch or limb which has been surrounded by subsequent growth of the wood of the trunk
or other portions of the tree.  A knot appears on the sawed surface, it is merely a section of the entire knot,
its shape depending upon the direction of the cut.

Cluster – Three or more knots in a compact, roughly circular group, with the grain between them
highly contorted, originating from adventitious buds.

Decayed Knots – A knot that, due to advanced decay, is softer than the surrounding wood.

Encased Knot – A knot whose rings of annual growth are not inter-grown with those of the surrounding wood.

Firm Knot – A knot which is solid across its face, but which contains incipient decay.

Fixed Knot – A knot which will hold its place in dry lumber under ordinary  conditions, but can be moved under
pressure although not easily pushed out.

Hole – A hole previously occupied by a knot.                                                    

Inter-grown Knot – A knot whose rings or annual growth are completely inter-grown with those of
the surrounding wood.

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.
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 – (Horn knot, Mule-ear knot, Slash knot)  A knot cut approximately parallel to its long axis, so that
the exposed section is definitely elongated.

Tight Knot – A knot so fixed by growth or position that it will firmly retain its place in the piece.
Knot hole is a hole previously occupied by a knot.
Lacquer   A finish containing nitrocellulose, more often used as a sealer. The fast curing properties of this finish
are created by using a solvent with a very low flash point which causes it to be very flammable.
Ambers little, cures rapidly, but may water spot and become cloudy when applied in high humidity.
Can be incompatible with some types of stains and topcoats.
Dries to tack free in 10-30 minutes, reaching full cure in 4-8 hours.
Lap   Used as a verb, lap means to lay or place one coat so its edge extends over and covers the edge of a
previous coat, causing an increased thickness where the two coats are present, as compared to the single
thickness on either side of the lap. As a noun, lap is that portion of a coat of finishing material that extends
over the edge of and onto a previous coat.
The portion of the annual growth ring that is found after the early wood formation has ceased.
It is usually denser and stronger than early wood (Summerwood).
Leveling The ability of a film to flow out free of ripples, pock marks, brush marks or other surface defects.
The separation of the growth ring, primarily at the tips, from the surface of a wood slit, especially on the
surface of plainsawn wood.
Lumber   The product of the sawmill and planing mill not further manufactured than by sawing, re-sawing, passing
lengthwise through a standard planing machine, cross cutting to length and matching.

Flooring Lumber – Generally, a grade of either hardwood or softwood boards that have been found to
produce maximum quantity of flooring of the desired quality.
A darkened area across the width of flooring caused by a machine.
Manufacturing characteristics described below include: Scant thickness, Saw marks, Skippy thin, Raised grain,
Wavy face, Torn grain, Mismatched pieces, Kinks, Planer bite, Off square end matching, Machine burns,
Rub marks, Rough handling, Edge deflects, Broken corners and Wane.
Strips of cells extending radially within a tree and varying in height from a few cells in some species to four
or more inches in oak. The rays serve primarily to store food and transport it horizontally in a tree. On quarter
sawn oak, the rays form a conspicuous figure, sometimes referred to as Flecks.
Meter Electronic Moisture Meter – An instrument used for rapid determination of the moisture content in wood
by electrical means.

Capacitance Type Electric Moisture Meter – A meter for determining the moisture content of wood by utilizing
the variation in the dielectric constant of wood with changing moisture conditions.

R. F. Power Loss Type Electric Moisture Meter – A meter for determining the moisture content of wood by
utilizing the variation in the wood dielectric loss factor with changing moisture content.

Resistance Type Electric Moisture Meter – A meter for determining the moisture content of wood by utilizing
the variation in wood electrical resistance with changing moisture content.
A solvent product used as a thinner and/or cleaner. Often known generically as “paint thinner”.
An olive to greenish-black or brown discoloration of undetermined cause in hardwoods, particularly hard
maples, which occurs in streaks usually containing accumulations of mineral matter.
A wood floor that is predominately of wood, but also incorporates other materials, such as slate, stone,
ceramic, marble or metal.
The amount of water contained in the wood, usually expressed as a percentage of the weight of the over
dry wood. NWFA hardwood flooring is manufactured at 6% to 9% Moisture Content, with a 5% allowance
for pieces up to 12% Moisture Content.

Average Moisture Content – The moisture content, in percent, of a single section representative of a larger
piece of wood or the average of all the moisture content determinations made on a board or other wood
item or of a number of determinations made on a lot of lumber or other wood products.
An oil based varnish enhanced with urethane.  This hybrid ambers well and has good abrasion resistance.
Curing may be delayed when humidity levels are high, which can lead to inadvertent damage such as
scratches. Very stain and abrasion resistant, but has a long curing time. Dries to tack free in 8-36 hours,
reaching full cure in 30-60 days.
Kiln Dried Moisture Content – The moisture content of wood that has been dried in a kiln; usually from
6% to 9% for thoroughly kiln dried stock.  
As the name implies, this finish cures in the presence of moisture and fails to do so in its absence of
strongly ambering or available in non-ambering. Very stain, spot and water resistant, but requires very tight
environmental control during application and curing. May cure too rapidly and flatten poorly when applied
in very high humidity. Long delays in curing may occur in areas when humidity levels are quite low.
The excellent abrasion resistance also makes this finish difficult to recoat. Dries to tack free in 8-24 hours,
reaching full cure in 14-30 days.
Mold A fungus growth on lumber or other wood products at or near the surface and, therefore, not typically
resulting in deep discolorations.  Mold is usually ash green to deep green in color, although black and yellow
are common.
Mosaic ParquetSee Parquet.
A diluted acid used to neutralize alkalinity of concrete subfloors.
Rough edge where the board is not wide enough to machine smooth on the groove side.
Natural Growth
The tree from which lumber and flooring is obtained is a product of the soil, moisture, air and sunshine
in constantly varying combinations. Throughout its life the tree is subjected to extremes of heat and cold,
flood and drought and has been buffeted by countless storms. As a result, wood is extremely variable
in structure and appearance. Along with this variability in structure and appearance, certain characteristics
occur in the wood because of the growing conditions and injuries. In addition, further characteristics
develop through the process of manufacturing and drying.
Nominal Size   As applied to timber or lumber, the size by which it is known and sold in the market, often different from
actual size.
Nosing   The rounded and projecting edges of the treads of a stair or the edge of a landing. Usually where these edges
are right-angled, in resilient floor installations, they are protected by a slightly rounded metal edging, also
called “nosings”
Off Square Any end that is not 90 degrees to the edge.
An oil based varnish enhanced with urethane. This hybrid ambers well and has good abrasion resistance.
Curing may be delayed when humidity levels are high, which can lead to inadvertent damage such as
scratches. Very stain and abrasion resistant, but has a long curing time. Dries to tack free in 8-36 hours,
reaching full cure in 30-60 days.
Open Grain A failure of finish to form a film over areas of low density, normally associated with the softer spring wood.
The finish is absorbed into the softer grain failing to form a film and causing a loss of sheen. While not
considered a finish defect, it can often be concealed by the application of an additional coat of finish.
A finish that exhibits a surface texture resembling the surface of an orange. Normally caused by rolling a
finish that has cured excessively which freezes the roller pattern in the film. May also be caused by excessive
air flow, the velocity of which freezes waves in the film when it sets.
Out of
Out of match flooring consists of pieces in which the surface of adjoining pieces are not in the same plane.
Overwood This term applies to two pieces of hardwood (usually square edge) where the surface of one piece is higher
than the next.
Parquet A floor of any non-linear pattern. Generally a tile composed of individual slats assembled together. A square
may or may not possess tongues and grooves to interlock and isn’t necessarily square or regular in dimension.
Peeling A defect in a dried film manifested by large pieces becoming detached from the under surface and coming
loose in sheets or large flakes.
Stains that penetrate into the surface of the wood. They are usually made of dyes dissolved into liquids
that easily penetrate the wood.
An integrated system of coating and coloring designed for the commercial market. An ultraviolet
cured urethane topcoat with aluminum and mineral oxide additives incorporated in the urethane.
The oxides increase wearability of the urethane finishes.
Another word for mineral spirits.  
pH Value The concentration of the hydrogen ion in a material.  A pH value of 7 is considered neutral.
Lower values are acidic; higher values are alkaline.  
Photo-sensitive The property of some wood species which causes them to lighten or darken when exposed to light.
Pigment The fine, solid particles used for color or other properties in the manufacture of paint and enamel.
Stains that get their color primarily from pigments mixed with binder and volatile thinners.
Pin Lines
Normally caused by finish flowing into low lying or less dense areas such as springwood.
This thicker film of finish allows gasses formed during curing to freeze in the film leaving a small crater.
The finish fails to form a film in these areas as the finish is in the wood instead of on it.  While not
considered a finish defect, it can be corrected by the application of an additional coat of finish.
Pin Worm
In hardwood flooring, a small round hole not over 1/16″ in diameter, made by a small wood boring insect
in the living tree. Allowed in all grades.  
Pith   The small, soft core occurring near the center of a tree trunk, branch, twig or log.
Lumber that has been sawed approximately tangent to the growth rings. Lumber is considered plain sawn
(flat grained) when the annual growth rings form an angle of 45 degrees or less with the wide surface
of the piece.
A groove cut in the surface of the face or edge of a slat, cut deeper than intended by the planer knives.
Plank Solid boards, usually 3/4″ thick and 3″ to 8″ wide designed to be installed in parallel rows. Edges may be
beveled to simulate the appearance of Colonial American plank floors.
Plugs   Dowels that simulate the Colonial American plugged or pegged plank look. They are used to cover
countersunk screws when installing wood flooring or for decorative purposes in wood flooring.
Polyurethane A large molecule of chemically joined urethane units, having the capacity to solidify or “set “. Irreversible
when acted upon by heat, radiation or chemical crosslinking or curing agents. See Urethane.
Beetles which derive their common name from the small piles of powder-like frass ejected from
holes bored when the mature insect takes flight. Destroyed in kiln drying through heat sterilization,
but may reinvest dry lumber.
Prefinished A completely finished flooring that required installation only.
Puckering The crinkling, shriveling or wrinkling of a coat of finishing material upon drying.
 Pure Free of adulteration.
Quantity   The amount, bulk, mass, weight or measure of a thing; a measure of its size or numbers.
Lumber that has been sawed so that the wide surface is approximately at right angles to the annual growth
rings. Lumber is considered quarter sawn (edge-grained) when the rings form an angle of 45 degrees to 90
degrees with the wide surface of the piece.
A condition when dense summerwood is raised above the springwood on the surface of a slat but not
torn loose. Usually caused by absorption of moisture.
Ray   In wood anatomy, a ribbon-like aggregate of cells extending radially across the grain, so oriented that the
face of the ribbon is exposed as a fleck on the quartered surface. See Medullary Rays.
Red Oak Color – Heartwood and sapwood are similar, with sapwood lighter in color; most pieces have a reddish tone. 
Slightly redder than white oak. Grain – Open, slightly coarser (more porous) than white oak. Plain sawn
boards have a plumed or flared grain appearance; quarter sawn has a flake pattern.
Reduce To lower the viscosity of a material or to thin it by the addition of a solvent, thinner, varnish, oil, etc.
Refinished Sanding a previously finished floor to bare wood and applying new finish.
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.
Retarder A slowly evaporating solvent that decreases the evaporation rate or slows up the drying of lacquers and
similar materials.
Rift Sawn Lumber (primarily hardwoods) in which the annual rings make angles of 30 degrees to 60 degrees with the
surface of the piece. Also known as bastard sawn.  
Porous Woods
A group of hardwoods in which the pores are comparatively large at the beginning of each annual growth
ring and decrease in size, more or less abruptly, toward the outer portion of the annual growth ring.
The large pores are springwood and the smaller pores are summerwood.
Rot In wood, any decay attacking both the cellulose and lignin producing a generally whitish residue that may
be spongy or stringy or occur in pockets.
In stacking wood items such as lumber or dimension stock for drying, or in the take-down of piles, unit
packages in kiln trucks, the breakage, splitting, gouging, tearing or general value loss due to carelessness
in moving the pieces, or damage caused by maladjusted mechanical equipment.
Updated on September 22, 2022