the process of creating a quality wood floor starts back in the forest

The
Cutting Edge
THE PROCESS OF CREATING A QUALITY
WOOD FLOOR STARTS BACK
IN THE FOREST
by Kim M. Wahlgren
Editor’s Note: This is the first of our three-part series on
How Wood Floors Are Made. This article follows the
process from tree to log to lumber. The February/March
issue will detail the manufacture of solid, unfinished
wood flooring, and the April/May issue will cover engineered and prefinished flooring.
W
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HARDWOOD FLOORS
hen you are out on the job, do
you ever stop during installation to think about all the
December 1998/January 1999
steps the wood flooring has gone through to
make it to your job site? Although it’s not a
relatively complicated product, the process
of creating wood flooring begins many
months or even years before the wood is
milled into a flooring profile and installed in
someone’s home. Years of forestry management and the work of loggers and sawmills
Photo courtesy of Georgia-Pacific Hardwood Lumber.
bring the lumber to a point where it can become wood flooring.
INTO THE WOODS
These days, most lumber comes from carefully managed forests. Opinions vary greatly on
how hardwood lumber should be harvested.
The methods fall roughly into four categories:
selection, shelter-wood, group selection or
clear-cut. What method is used depends mainly on the opinion of the forest manager.
Proponents of single-tree selection
choose their method based on the species
that they are trying to establish and the
amount of light these species need in order
to grow well. Species such as sugar maple
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HARDWOOD FLOORS
23
Photo courtesy of Tembec Inc.
A trained tree marker designates this tree
for removal.
Photo courtesy of Tembec Inc.
Logs are dragged out of the forest using
a skidder.
Photo courtesy of Tembec Inc.
The selectively harvested area on the left shows
the difference in light levels as contrasted with
the unharvested area on the right.
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HARDWOOD FLOORS
December 1998/January 1999
and beech are “tolerant” hardwoods,
meaning that they will grow in the shade
of other trees. Such trees can be managed by selective harvesting, in which
enough trees are harvested so that the
forest canopy is opened up to allow
about 30 percent of the light to reach
the ground. For “mid-tolerant” species
such as oak, yellow birch, black cherry
and ash, shelter-wood harvesting proponents open up the canopy more, to
about 40 percent. People using these
methods also use clear-cutting for
species such as white birch, aspen or
poplar, all of which do not grow well in
the shade of other trees.
Selective and shelter-wood harvesting
involve single-tree selection; that is, before
the trees are cut, an inventory is made of
the forest tallying species, size and quality. Their information is then compiled, and
a prescription for cutting that forest is formulated. Trained tree markers then paint
individual trees for removal according to
the forest prescription.
Until about 25 years ago, “logger’s
choice” was sometimes used as a sort of
single-tree selection, meaning that the
loggers would simply go in and cut the
best trees. Although that still occurs
today, some managed forests use reverse-high-grade operations, taking out
only the poor-quality stock. The bestquality trees remain as the future growing stock, just as a garden of vegetables
is thinned to produce the best results,
and the cut trees allow light to reach
the young seedlings and saplings. Proponents of this method say that it results both in better-quality and fastergrowing forests for the future.
With this process, the treetops are
cut off onto the forest floor, making the
log easier to pull out of the forest with
smaller equipment. It also helps avoid
the damage branches would do to the
future growing stock as they were
dragged out of the forest. Additionally,
the treetops and debris that are left behind benefit the smaller animals of the
forest while returning nutrients to the
forest floor.
Other forest managers take a drastically different view. They prefer the cutting method of group selection, which is
essentially patches of clear cutting that
can range in size from 1 to 10 acres. It
gives managers the advantages of clear
cutting without the unsightly result of a
large clear cut. With this method, managers cut down areas of timber that are
Photo courtesy of Tembec Inc.
Seen
from a
distance,
the
completed
selection
harvest
across
the lake
is difficult
to detect.
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HARDWOOD FLOORS
December 1998/January 1999
undesirable or understocked, as well as
some areas of mature timber. If they
want to cultivate a certain specie, they
may replant it in the cut area. More likely, they leave the area to do what they
say hardwood does readily — regenerate itself. The natural regeneration can
occur from root sprouts, stump sprouts
or seedlings.
Group selection proponents say that
selective cutting does not work in a hardwood forest, because the remaining trees
develop epicormic branches — areas
where new branches sprout out from the
trunk. These new branches create a knot
within the timber and degrade the lumber from that point on. Advocates of
group selection also point out that hardwoods tend to have large crowns, which
cause excessive damage to surrounding
trees as the single tree is felled.
Whichever method is used, the loggers go into the woods with a careful
plan of exactly what they are cutting.
Photo courtesy of Tembec Inc.
Large machines generically referred to
as feller bunchers do most of the cutting, with chain saws also used for the
larger trees. Although some horse logging is still done, most of the logs are
pulled out of the forest with a skidder,
which pulls out the logs using steel cables and a winch.
In the United States, the U.S. Forest
Service has grades for logs: Veneer,
One, Two and Three, while in Canada
the log grades are Grade 1 and Grade 2.
Graders look for visible defects on the
tree, such as areas where branches had
been cut or where there is rot, and
grade accordingly. The Veneer grade is
the highest quality. One-grade logs will
become the highest grades of lumber,
Two-grade become a medium grade of
lumber, and Three-grade logs eventually will go to uses such as wood for pallets. All grades of lumber come out of
each of the log grades, although the
percentage of each grade of lumber
changes as the log grade goes down.
Logs head into the mill on the infeed deck.
Photo courtesy of Georgia-Pacific Hardwood Lumber
INTO PRODUCTION
At the sawmill, the first step for the
logs is the debarker. Essentially like a
giant pencil sharpener, the debarker
takes the bark off all sides of the log in
a single process. The shaved logs are
then rolled on the carriage, where a log
turner turns the log so that the best
face can be selected to produce the
best yield. Many mills have a computer
with laser optics to select the first cut
of the log, and a slab is cut off there, resulting in the log’s first flat side. The
cut slab may go into a chipper, or in
high-production mills this slab may go
to another saw, a horizontal resaw.
With one flat side, the log is then cut
into long slices. As the cutting approaches the heart of the log, the log is
turned (typically 180 degrees) and cut
from a new direction. This process is
either accomplished by a band mill,
which is essentially like a large band
saw, or by a circle mill, which has a
large blade and is similar in function to
a circle saw.
These long boards of the log still have
rough edges and some bark left on them,
so they are taken off the carriage and
head to the edger, which trims most of
the wane (where lumber doesn’t reach
the full width of a board) and bark off.
Next a double-end trim saw takes off defects from the ends of the board such as
bark ends and splits, and may cut the
After the debarker, a slab is cut off one side
of the log.
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HARDWOOD FLOORS
29
board to a desired length.
This clean lumber is of varying dimensions. It may be anywhere from
1 to 4 inches thick, 4 to 16 feet long,
and a minimum of 3 inches wide,
going up to as wide as the saw is capable of cutting.
MAKING THE GRADE
Now the lumber is ready for grading.
Lumber grades in the United States
and Canada are determined by the
National Hardwood Lumber Association, based in Memphis, Tenn.
(The Canadian Lumbermen’s
Association adopts the NHLA grades
verbatim and distributes the rules in
Canada on behalf of NHLA.) Although
NHLA’s grades may vary slightly for
different species, the standard
grades range from highest to lowest
quality: FAS, FAS One Face (F1F), Select, No. 1 Common, No. 2A Common,
Photo courtesy of Georgia-Pacific Hardwood Lumber
A band mill cuts the log into
long boards.
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HARDWOOD FLOORS
December 1998/January 1999
No. 3A Common, No. 2B Common,
No. 3B Common, and Wormy. Although lumber and flooring grade
names are similar or identical, the
grade of lumber does not dictate the
grade of flooring. Thus, No. 1 Common lumber will not necessarily produce No. 1 Common flooring.
FAS and F1F are used for high-end
work, such as specialty millwork.
No. 1 Common is the standard used
for the furniture and cabinet industries. By far, the most often used
lumber grades for hardwood floors
are No. 2A Common and No. 3A
Common. However, some flooring
manufacturers, especially plank producers (who need to maintain quality across a larger area of flooring),
may use No. 1 Common. AdditionalPhoto courtesy of Georgia-Pacific Hardwood Lumber
An optimizing edger
determines what the width of
the board will be.
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HARDWOOD FLOORS
December 1998/January 1999
Photo location: Superior Floor Company
ly, market demand for No. 2A Common
and No. 3A Common has continued to increase in recent years, as cabinet and
furniture makers move into a lower
grade of lumber. This has caused some
flooring manufacturers to buy No. 1
Common in order to maintain a lumber
supply.
BOUND FOR FLOORING
Stacked lumber is air dried before heading
to the kiln.
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HARDWOOD FLOORS
December 1998/January 1999
Now separated by grade and species,
the lumber heads to the flooring mill,
ideally within days of being sawn. There
it is stacked with sticks — wooden
strips placed between layers of lumber
to permit air circulation — and either air
dried or predried. If it is air dried, it can
take a matter of months, depending on
the wood’s moisture content and the
weather. Predrying the lumber, in which
it is stacked in large, atmospherically
controlled buildings, can result in fewer
moisture defects such as checking and
can take a shorter period of time. In
areas of the South, however, air drying is often faster than predrying.
After the initial drying, the moisture content of the wood is usually
in the low 20 percent range before it
heads into the kilns, essentially
large ovens that remove most of the
moisture from the wood and sterilize it from insects and other contaminants. The kiln temperature ranges
anywhere from 100 to 108 degrees
Fahrenheit, with dry kiln schedules
typically ending between 160 and
180 degrees Fahrenheit. Kiln types
vary, with dehumidification kilns,
steam kilns and dry heat kilns all
used. The most technologically advanced kilns are carefully controlled
by computers that continually meaPhoto location: Superior Floor Company
Kilns dry and sterilize
the lumber.
sure temperature, humidity, air flow,
vent capacity and moisture content
at points throughout the kiln. At the
end of its time in the kiln, the lumber has a specific moisture content
of, for example, 7 percent.
To cool out, the stacked lumber is
placed in cooling sheds for the necessary period of time; then it is ready
to head into the flooring mill. ●
Contributors to this article included:
Bobby Millner, National Oak Flooring
Manufacturers Association; Keith Waldrop, McMinnville Manufacturing; Milton Loughridge, Buchanan Timber
Co.; Tracy Cook, Linden Lumber Co.;
and Gerald Kroes, Tembec Inc.
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