Key Characteristics of Solid Wood Materials
by Secondary Wood Products
Manufacturing Segment
JOHN PUNCHES1
OREGON STATE UNIVERSITY DEPARTMENT OF WOOD SCIENCE & ENGINEERING
MARCH 6, 2002
Manufacturers of secondary wood products use solid wood in a variety of applications. In each
application, solid wood must meet performance criteria related to the customer’s expectations
(generally related to appearance) and the manufacturer’s design and manufacturing process.
Case studies (including site visits and personal interviews) of 53 secondary wood products
companies conducted between 1999 and 2001 identified characteristics important in solid wood
applications in each of five industry segments. Characteristics of solid wood materials
necessary in particular products, including specific information about the defects or character
marks allowed, were determined. Raw material species and grades were identified, as were the
products’ intended uses, finishes, and mechanisms of fastening. Performance criteria included:
Appearance Characteristics: Uniform Color, Specific Grain Pattern, Presence of Burl,
Heartwood or Sapwood
Grain Characteristics: Fine Grain, Vertical Grain, Straight Grain
Physical/Mechanical Characteristics: Strength (low, medium, high), Texture (fine, medium,
coarse), Surface Hardness, Density, Abrasion Resistance, Shock Absorbance, Stability (low
shrink/swell), Straightness (low warp, crook, bow, twist)
Drying Characteristics: Dries Quickly, Dries Easily, Dries with Minimal Degrade
Machining Characteristics: Cuts Well, Edges Well, Surfaces Well, Sands Well, Steam Bends
Well, Fingerjoints Well
Allowable Defects: Pin Knots, Sound Knots (by size), Loose Knots (by size), Wormholes,
Stain, Discoloration, Pith, Gum/Pitch Pockets, Wane, Bark Pockets, Surface Checks, End
Splits
Results, listed below, are stratified by industry segment and type of application. Drying
characteristics are not included, as only one of the case study companies (a flooring
manufacturer) dried its own wood raw materials. In this report, the category “natural appearance
applications” includes products that, following assembly or installation, will be visible and be
finished with stain, clear finish, or no finish at all. “Painted applications” includes products that
will have an opaque finish. “Hidden/structural” includes components that will be covered by
other wood, upholstery or laminate, or will otherwise be hidden from view in the completed
application.
The information reported provides insights into how the secondary wood products industry uses
solid wood and the characteristics it requires in broad categories of applications. It is qualitative
at best, and should not be assumed to represent the “average” company in any particular
category or to accurately represent every company in any particular segment. Wood use and
acceptable wood characteristics vary widely among industry segments, individual
manufacturers, and specific products.
1
John Punches. Associate Professor. Department of Wood Science & Engineering. Oregon State University.
Stationed at: Douglas County OSU Extension Service. 1134 SE Douglas Ave., PO Box 1165. Roseburg, Oregon,
97470. Phone: 541-672-4461. Fax: 541-672-4453. E-mail: [email protected].
Architectural Millwork
Natural Appearance Applications
Uniform color is critical in natural appearance millwork applications. Either heartwood or
sapwood is specified, depending on species. Grain pattern and/or orientation (plain/quarter/rift)
is specified in many applications. Occasional pin knots are allowed by most manufacturers,
otherwise material is essentially free of defect. Gum/pitch pockets are allowed in most cherry
applications. Larger knots are allowed in knotty pin but otherwise excluded. Architectural
Woodwork Institute (AWI) standards tightly proscribe allowable defects in millwork (along with
other characteristics including flame spread rate). Stability and straightness are critical, and
material may need to be hard enough to resist denting. Manufacturers prefer species that cut,
edge, surface and sand cleanly, but customers or architects typically specify species and
manufacturers must tailor processes accordingly. Steam bending appears to be infrequent, and
fingerjointing extremely uncommon. Mechanisms of fastening include glue (very common),
dowels/pegs, screws, staples/pins, and to a lesser extent biscuits, nails, mortis and tenon, and a
variety of specialized systems. Commonly utilized species include hard and soft maple, red and
white oak, cherry, walnut, mahogany, and yellow-poplar, in FAS or higher grades and eastern
white pine in equivalently high grades.
Painted Applications
Color and grain are not critical in painted millwork applications. Manufacturers often seek fine
textured species that will take paint well and finish smoothly. Pin knots are allowed, as are stain
and discoloration provided they will not show through the finish. Small, tight knots and other
small defects that can be filled and will not show through the surface are tolerated by many
manufacturers. Loose knots, decay, wane, pith, bark pockets, large wormholes and end splits
are rarely tolerated. Stability and straightness remain critical, and material may need to be hard
enough to resist denting for specific applications. Manufacturers prefer species with good
overall machining characteristics, but often must tailor processes to species dictated by a
customer or architect. Fingerjointing appears to be rare. Mechanisms of fastening are the same
as noted for natural appearance applications. FAS yellow-poplar and soft maple are commonly
purchased for painted millwork, but much is produced from falldown from higher grade products.
Hidden/Structural Applications
Color and grain appearance are not important in hidden millwork applications. Pin knots are
allowed, but other knots may be excluded. Other defects are typically allowed as long as
material is sufficiently solid to perform structurally and/or as a fastening medium. Materials must
be straight and stable for most applications. They must cut moderately well, but other machining
characteristics are of lesser importance. Hidden materials are more likely to be fastened with
screws, staples, pins, or nails than in appearance or painted applications. Poplar is a common
species in hidden applications, and its source is generally falldown from other products.
Construction lumber is used for general framing, and plywood is used under panels and,
increasingly, ripped and glued up to serve in place of construction lumber.
Moulding
Natural Appearance Applications
Uniform color is critical in natural appearance moulding applications. Heartwood or sapwood will
be specified depending on species. Uniform and/or straight grain is important to some
manufacturers. Pin knots are generally allowed. Occasional, larger knots are allowed by some
manufacturers, although they are likely to be cut out by the installer. Most manufacturers avoid
other defects, but a few allow minor stain or discoloration, gum/pitch pockets in cherry, and
occasional small wormholes. More frequent and larger defects are allowed on the back.
Straightness is very important and stability is important to some manufacturers. Dent resistance
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may be desired for some applications. A clean, smooth surface is required in the finished
product, but species is often dictated by the customer and manufacturers must tailor their
machining processes to the species. Staples/pins are the most common mechanism of
fastening. Glue is also common, and screws are used occasionally. Red oak, maple, cherry,
yellow-poplar, eastern white pine, ponderosa pine and hemlock are common species. Grades
are typically high, including FAS for hardwoods and D and Better or shop grades for pine.
Painted Applications
Color and grain need not be uniform in painted millwork. Fine textured species may be preferred
for a smooth, painted surface. Pin knots are generally allowed, and stain and discoloration are
allowed if they can be covered by the finish. Some manufacturers tolerate tight knots and to a
lesser extent wormholes, pith, and surface checks – as long as they can be puttied and finished
smooth. Straightness is very important. Stability is important to many manufacturers. Dent
resistance is important in some applications. Manufacturers prefer materials that cut, edge,
surface, and sand well, but species are typically dictated by the customer. Some fingerjointing is
done in painted moulding. Staples/pins are the most common mechanism of fastening. Glue is
also used, as are nails and occasional screws. Yellow-poplar is preferred for many painted
mouldings, and is frequently purchased as FAS for higher grade products and the falldown used
in this application. Much painted moulding is produced from MDF.
Doors & Windows
Natural Appearance Applications
Uniform color is critical in doors and windows. Either heartwood or sapwood will be specified,
depending on species, and wild grain patterns will usually be avoided. Windows often require
straight grain, and where Douglas-fir is employed it will generally be sawn to have vertical grain
and a minimum ring count may be specified. Occasional pin knots are allowed in most door and
window applications, but other defects are rarely tolerated. Some manufacturers and/or
applications utilize only defect-free material. Wood used for doors and windows must be straight
and reasonably stable. Dent resistance may be in issue in some applications, and decay
resistance is necessary for exterior use. Preservative treatments may be employed to enhance
decay resistance. Manufacturers prefer species that cut, edge, surface and sand well, but tailor
their processes to the species dictated by their customers. Steam bending and fingerjointing
appear rare in these applications. Mechanisms of fastening include gluing, dowels/pegs,
screws, staples/pins, mortis and tenon, and nails. Common species for windows include
ponderosa pine, eastern white pine, radiata pine, and Douglas-fir (vertical grain) in very high
grades (e.g., highest export grades or sorts exceeding FAS). Exterior doors are typically
produced of eastern white pine, mahogany, white oak, and Douglas-fir, while interior doors
employ a broader range of species. High grades such as FAS (hardwoods) and D and Better
(pine) are common for doors.
Painted Applications
Color and grain uniformity are not important in painted door and window applications when the
entire component is painted or hidden. (Many components, particularly in windows, have only
one surface painted and the other remains visible. In these cases the requirements of the
natural appearance application take precedence.) Manufacturers may prefer fine textured
species that will yield a smooth painted finish. Pin knots are generally allowed. Stain and
discoloration are allowed where they can be successfully covered by the finish. Very minimal
other defects are generally tolerated, but they must putty and finish smooth. Material for these
applications must be straight and smooth, and dent resistance is desired in some applications.
Machining and fastening requirements differ little from natural appearance applications. Yellowpoplar, ponderosa pine, radiata pine, and eastern white pine are employed in their high grades,
along with some fingerjointed stock and falldown from other products.
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Hidden/Structural Applications
Doors and windows utilize glued-up components primarily for the purpose of improving stability
and ensuring straightness of the finished product. This leaves the cores of flat-panel doors and
parts of doorjambs, stiles, and rails hidden from view but playing critical roles in the product’s
performance. Color and grain appearance are not important in these applications. Pin knots,
stain and discoloration are generally allowed. Acceptance of other knots varies among
manufacturers and products. Other defects that will not show through a surface veneer or
otherwise negatively impact performance are typically allowed. End splits are not tolerated.
Straightness is critical, and conditioning (lack of tension) is important to ensure material remains
straight in the remanufacturing process. Stability is important, but is addressed in the design of
glued-up components. Good machining properties are necessary, as flat surfaces are needed
for gluing. Glue, dowels/pins, screws, staples, pins and nails are common fastening
mechanisms. Many species of pine, plus fir and hemlock, are commonly employed in these
applications, in grades of #2 and #3 Common. Fingerjointed material is also employed, along
with composites such as laminated veneer lumber and laminated strand lumber.
Furniture
Natural Appearance Applications
Uniform color is critical in natural appearance furniture applications, particularly those with light
colored finishes. Heartwood or sapwood will be specified, depending on species. Grain pattern
and/or orientation (quarter, rift, or plain sawn) may be specified in some applications. Slope of
grain is important in structural applications (e.g., frames and legs). Pin knots are allowed in
some applications. Gum/pitch pockets are allowed in cherry, and knotty pine allows large, sound
knots and pitch pockets. Other defects are excluded in nearly all applications. Straightness and
stability is important in most applications. Legs and frames require reasonably high strength
material. Impact resistance may be an issue in legs. Manufacturers prefer species that have
good overall machining characteristics, but must often tailor their processes to species dictated
by customers. Fastening mechanisms include glue, dowels/pegs, screws, staples/pins, some
biscuits and dovetails, mortis and tenon, and a variety of special fasteners. Species common in
these applications include hard and soft maple, yellow-poplar, red oak, ash, mahogany, walnut,
and eastern white pine in FAS, #1 and #2 Common, and Select and Better grades or the pine
equivalents.
Painted Applications
Color and grain are not critical in painted furniture applications, as long as a uniform finish can
be achieved. Requirements for painted furniture applications are otherwise nearly identical to
those for natural appearance furniture applications. Only minimal defects are tolerated and
requirements for stability and other mechanical/physical properties remain unchanged. Yellowpoplar and maple are common species for painted furniture components. They are purchased in
a range of grades. Falldown from natural appearance products is also employed.
Hidden/Structural Applications
Color and grain appearance is not important in furniture’s hidden applications. Slope of grain is
often a key consideration. Pin knots and some sound knots, stain and discoloration are
generally allowed. Some applications allow other defects as long as they are sound. Defects
must not interfere with fastening or otherwise negatively impact performance. Thus, some
hidden applications (including portions of furniture frames) will allow only stain and discoloration
and exclude all other defects. Straightness and stability are key considerations, and strength is
important in many applications. Some applications limit wood density to ensure successful
stapling. Screw holding capacity is important in some applications, and impact resistance is
important in leg components. Good cutting characteristics are desired. Other machining
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characteristics are typically of less importance. Fastening mechanisms are consistent with those
employed in natural and painted applications. Yellow-poplar and maple are commonly utilized in
these products, often gleaned from falldown from higher grade products. If purchased, it is
typically of FAS or #1 Common grade. Many hidden furniture components are manufactured
from plywood, which is favored for its uniform strength and stability.
Cabinets
Natural Appearance Applications
Uniform color and grain are critical in natural appearance cabinet applications. Many
manufacturers sort material to match color and grain within individual assemblies. Heartwood or
sapwood will be utilized depending on species, and grain orientation may be specified. Pin
knots are allowed by most manufacturers. Gum/pitch pockets may be tolerated in cherry. Other
defects are rarely tolerated. Some manufacturers exclude all defect, using “perfect” material.
Significantly more “character” is allowed in rustic grades or species known for their variation
(e.g., hickory or knotty pine). Material must be straight and stability is desired. Some
manufacturers consider dent resistance when choosing materials. Good cutting, edging,
surfacing and sanding characteristics are desired, but manufacturers tailor their processes to
the species dictated by their customers. Primary mechanisms of fastening include glue, screws,
staples/pins, and to a lesser extent dowels/pegs, biscuits, and mortis and tenons. Red oak,
white oak, maple and cherry are perhaps the most common cabinet species, but many other
species are employed at customers’ requests. Light colored species are currently in vogue. FAS
and 1 Common raw material grades are commonly utilized, often with additional restrictions on
color variation.
Painted Applications
Color and grain appearance is not important in painted cabinets. Pin knots are allowed, and
stain and discoloration are accepted as long as they do not show through the product’s finish.
Other defects are typically excluded unless they can be puttied smooth. The manufacturer’s
objective is a smooth, uniform surface. Material must be straight and may require dent
resistance. Machining requirements and fastening mechanisms mirror those of natural
appearance cabinet applications. Yellow-poplar, maple, and alder, (mostly in the #1 Common or
equivalent grade) are employed, along with falldown from higher grade products. MDF is used
extensively for painted, veneered, or laminated cabinet panel components.
Hidden/Structural Applications
Hidden applications in cabinets include glue/fastening blocks and various structural braces.
Appearance is not important – the components need only serve adequately as supports or
points of fastening. Defects that would interfere with their performance are not allowed. These
components are typically produced from plywood or falldown from other products.
Flooring
Solid Wood
Solid wood flooring is available as strip, plank or parquet products (differing primarily in piece
size) and in four generally accepted grades. High density, dent resistant species are best suited
to flooring applications, but almost any species is utilized at customers’ requests. Straightness
and stability are important. Abrasion resistance is achieved through finishing. Manufacturers
prefer species with good machining characteristics, but tailor their processes to the requested
species. Thin flooring (1/2” or less) is commonly glued down, while standard thickness flooring
is pinned or nailed. Red and white oak, maple, cherry, ash, and walnut are common flooring
species, and manufacturers generally purchase these materials in FAS to #2 Common lumber
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grades. Flooring grades are defined by industry organizations, but there are also many
proprietary grades. The top grade (Clear) is extremely uniform in color and virtually defect-free.
Grain orientation (quarter, rift or plain) is often specified. Flooring’s second grade (Select) allows
some variation in color, including natural variation between heartwood and sapwood and very
limited amounts of stain or discoloration. Defect is still very limited, but generally includes pin
knots and limited numbers of very small tight knots. Some manufacturers allow small wormholes
and minor surface checks. The third grade (1 Common) includes a mixture of color and grain
appearance, pin knots and larger sound knots, small loose knots, wormholes, incipient decay,
stain, gum pockets, wane on back edges, partial tongues, small bark inclusions if solid, short
splits, and surface checks. The fourth grade (2 Common or rustic) allows wide variation in color
and grain and almost any defect.
Wood Composite
Composite flooring utilizes a sliced or peeled veneer face on a plywood core. It generally has
the appearance of a Clear or Select solid floor. It may be prefinished or impregnated with
plastics to assure surface durability. Good machining characteristics are desired. Most
composite material is glued down, or may attach only to adjacent pieces and float over a
substrate. Oak, maple, ash, and cherry are common, but many other species are utilized.
Appearance layers are typically produced from high quality lumber or thick veneers. They allow
some pin knots (slightly larger in some products) but are otherwise clear.
Miscellaneous Solid Wood Products
Several products encountered in this study do not fit neatly into one of the five major categories
described above. These miscellaneous products include trophy bases, plaques, small display
cases, educational unit blocks, butcher blocks, caskets and casket parts, edge-glued panels
and laminated squares, and decorative inlays for wood floors. Each of the products is intended
for appearance applications with stained or clear finishes, or no finish at all. Uniform color is
thus of key importance. Grain orientation may be specified. Most applications allow little or no
defect, although as with other products gum/pitch pockets are typically allowed in cherry and
knots in knotty pine. Straightness is important in nearly all applications – stability to a lesser
extent. Surface hardness is important in some applications. Abrasion resistance, where needed,
is achieved through the finish applied. Educational unit blocks require wood of fine texture that
will not splinter. Good overall machining characteristics are typically desired, but customers
often dictate species and manufacturers adapt accordingly. Gluing is the most common
mechanism of fastening, but many others are utilized as well. Maple, cherry, walnut, yellowpoplar and eastern white pine are commonly employed for the products encountered, and
manufacturers utilize high grades of raw material (FAS or equivalent).
© 2002 Oregon State University. Not to be published or distributed without the author’s express
permission.
This publication was produced and distributed in furtherance of the Acts of Congress of May 8 and
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Department of Agriculture, and Oregon counties.
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