While there are other species, or types, of
wood used for flooring, the vast majority in this country is oak, for reasons
stated in the history section. The other species will have properties and
behavior similar to oak, so for simplicity's sake we will address ourselves in
this section only to oak.
The Living Tree
To begin with the basic, an oak tree grows with
roots in the ground and leaves in the air. Easy. The roots collect moisture
and nutrients from the soil and ship them through vessels or fibers up the
trunk and branches to the leaves. These vessels are similar to the
"strings" in a stalk of celery. The leaves mix the moisture,
nutrients, carbon dioxide, sunlight and bingo-photosynthesis gives oxygen back
into the atmosphere and food for the tree. The food is then shipped through
other vessels, throughout the tree and back to the roots. Growth occurs.
Basic.
The foregoing is fact and logic to help
understand that an oak tree is made up of fibers aligned vertically in the
standing tree. Cut the tree down and the fibers are horizontal. Saw boards and
manufacture strip flooring, nail the floor down and the fibers are still
horizontal and running the length of the boards.
In the standing tree the fibers are loaded with
moisture. The tree, after felling, begins to dry out, just like a rose wilts
after being picked. As the fibers dry, they shrink in thickness or diameter,
almost none lengthwise. This shrinkage, characteristic of oak (all woods) is
of vital importance in the understanding of oak flooring, so let's examine it
further.
Reasons for Moisture and
Shrinkage
While the figures used in this example are not
accurate, they help tell the story.
- A standing oak tree is felled in the forest
and sawed immediately into a board 1 " thick, 10" wide and 8'
long. Placed on a scale, the board weighs lOO pounds.
- This same oak board is placed in a stack of
boards separated from its neighbor by stacking strips of uniform size to
keep the board straight. The stack is aimed at the prevailing breezes to
accelerate drying, and again this location is in our southern states
enjoying many long warm months. The board stays in the stack for four to
six months and again we put the board on the scales. It now weighs-50
pounds. Fifty pounds of water has evaporated.
There are times today a mill must reach out
200 to 300 miles for lumber. With high rail and truck freight costs, the
need for air drying and not paying freight on water is obvious. Subtle,
however, is the companion fact that there must be this time allowed,
thereby making it difficult for the industry to immediately respond to an
upsurge in demand. Also, with today's raw lumber cost, the flooring
manufacturer must have enough capital to buy lumber and let several
millions of dollars sit in a field doing nothing but drying.
- Now our 50 pound board is trucked to the
flooring mill and loaded into a dry kiln.
The kiln is a
concrete building many times large enough to hold 3 or 4 railroad box
carloads of lumber. Within the kiln there are fans to circulate the air,
steam pipes to create heat, and live steam to induce moisture. Our board
is very gently treated by a highly-trained specialist. As he gradually
lowers the humidity and increases the temperature over a five to seven day
period until our board reaches the optimum moisture content for flooring
manufacture of about 8%. During the process the temperature in the center
of the board must reach 105°F to sterilize the eggs of a little fellow
named Lyctus who likes to eat oak floors. The board is too hot to touch,
so after a couple of hours, we again place the board on the scales-42
pounds.
Controlling Moisture
Content is Most Important
If we had an autoclave, or oven, into which we
could place the whole board and dry every bit of moisture out of the wood, the
board would weigh 40 pounds, but this 2 pounds of moisture remaining in the
wood keeps the wood "alive" and flexible.
Precision kiln-drying and the resulting
moisture content (M.C.) is one of several primary responsibilities of the oak
flooring manufacturer. The correct M.C. makes oak flooring predictable.
Violate the M.C. and all kinds of things happen. Dry oak flooring (made from
these dry boards) is like a blotter. The boards really want to regain some of
their lost moisture. All of us-manufacturer, distributor' retailer' truck
driver, builder (see Builder
checklist), installer, housekeeper, and owner-have the responsibility
to keep oak floors dry. Here's why.
When we began this story our board weighed 100
pounds and measured 1 x 10"- 8 ft. The vessels and fibers were full of
moisture. Now' after drying, the board weighs only 42 pounds and measures 3
1/32 x 9 1/8 -8ft.
The board has withered just like the rose. Each
vessel and fiber is smaller in diameter or width and has shriveled up. This is
why the board is narrower and a little bit thinner, but not shorter.
Think of the vessels as soda straws. Introduce
dampness or moisture to the floor and the moisture will be drawn into the end
grain (vessel ends) quickly. The fibers will accept this moisture and start to
swell or fluff up. If the moisture is of short-lived nature, the ends of its
boards will swell, get wider, and display what we in the industry call
"fishtail" (for obvious reasons). Long-term dampness will cause all
the boards to swell, called "expansion".
An expanded floor, given a chance to dry out, displays "shrinkage"
and results in cracks between boards.
To summarize on this property of
wood, oak floors in particular:
White and Red Oak Characteristics
Now let's go back to vessels-this
time looking at the cut end of pieces of oak flooring. The entire family of
oak trees (Quercus) is divided into two types-- the Albas and the Rubras-White
and Red. Within each of these groups there are many cousin varieties, but
generally, so far as flooring (and we use them all) is concerned, each group
has certain characteristics that are individual and infallible. White oak is
usually yellow to gray in color' is harder-stiffer-brasher. It sands smoother
than red, and comprises about 35-40/c of the forest (because that's the way
Mama Nature planned it). Red oak
is usually pinkish tan in color' is a little more flexible or soft, takes
stain or bleach better than white, and comprises about 60 to 65% of the
forest. Now Mama fools us! There are pink/tan white oak
boards and yellow/ gray red oak boards. How can you be sure?
White Oak Preferred for Whiskey
Barrels
Look at the vessels on the cut
ends of the board. Red oak appears to have a band of tiny holes running across
the end of the board. White oak has no tiny holes. The vessels in red stay
open -take a piece of red oak and blow through it into a pail of water-
bubbles! As a white oak tree matures the vessels in the inner portion of the
tree fill up with a deposit called tyloses. Hence, the difference in
appearance of cut ends, and stiffness, and hardness, and sanding, and stain
appearance. White oak is used for whiskey barrels rather than red since the
tyloses plug the vessels (straws) and who wants a leaky barrel?
The large vessels, (tiny holes)
that you can see with the naked eye are fibers formed during the early spring
months when winter has broken, rains are plentiful, and the earth rejoices
with rapid growth. This less dense portion is obviously called
"springwood." As rainfall lessens and days heat up, growth slows
down and produces dense "summerwood." The tree remains dormant from
November through February. The combination of one springwood and one
summerwood is called an annual ring-one years growth. Read the rings, as we
all know, and learn the age of a tree while the width of the rings tells of
drought, fires, rains, etc. Looking at a piece of flooring, follow the
springwood from the cut end around to the face of the board and you will see
that the springwood gives the board its grain pattern or face character.
Summerwood is the denser more uniform area between the grain flair. 
Plain or Flat Sawn Versus Quarter Sawn or
Quartered-
See Wood
Flooring CUTS & GRADES
With annual rings in mind, the
great oak tree maker decided that oak boards will expand and contract with
moisture change, parallel to the annual rings. The word in geometry is
"tangential." And this too is logical, realizing the dense, strong,
summerwood holds the springwood in place, while the springwood is freer to
swell "sideways. " The oak flooring industry makes constant use of
this property.
Flooring manufactured with grain
or annual rings running across the width of the boards is called
"plain," or "flat" sawn. Flooring with grain running at
right angles to the face or across the thickness, is called "quarter
sawn," or "quartered." Both types of boards can be cut from the
same log, as shown in the diagram. 
The difference in how the flooring
behaves is significant since plain sawn expands and contracts across the width
of the board, while quartered in theory get thicker and thinner. Quartered has
considerably more dimensional stability and does not respond to season change
as does plain. Using this property, many old Eastern homes in this country had
their oak floor installed after the base was applied to the wall and the oak
floor was fit tight to the base-years ago-with no problems-quarter sawn
flooring only. To install in the same manner today guarantees failure. Why?
Today the saw mills cutting the
logs into boards will produce about 80 percent plain to 20 percent quartered
lumber. With the tremendous loss in productive capacity in the industry, the
remaining flooring mills can no longer afford the expense of separating the
lumber. Quartered oak flooring is extremely hard to find, and expensive. Most
of all the production is mixed cut.
Controlling the expansion of oak
has been one of the elusive goals of the industry since its inception. The use
of quartered flooring was successful, but met an economic fate. To question
the problems caused by expanding oak gives need for these examples.
-
Expanding oak floors may cup,
buckle (graphic), raise off the subfloor, even push walls out.
-
Whiskey barrels swell tight
and hold for years, drain and dry it-it leaks.
-
And the power generated by
each little fiber swelling was best illustrated by early Romans. The huge
blocks of granite and marble used to build Roman cities were
"cut" out of mountains by drilling holes with a hand auger,
hammering dry oak pegs into the holes, and soaking the peg ends with
water. The peg expanded and -pop - the oak splits the mountain.
The control of expansion in
today's oak flooring rests with proper handling and maintenance, but mostly
with the installer using proper methods.
New Products Minimize Expansion
Problems
The oak flooring industry has,
however, developed product types to minimize expansion problems.
-
5/16 thick parquet.
-
Acrylic impregnated.
-
Laminated floors.
Making use of the nature of oak
and the fact that 80% of their incoming lumber is plain sawn, manufacturers of
5/16 parquet gang rip the boards through their thickness, turn the resulting
slat flat and now 80% of the slats are quartersawn (the other 20% are plain). 
To further aid in gaining
stability, these slats, now called fillets, are spaced during assembly (into
units) to provide hairline expansion space between fillets. The result of
using 80~% quartered fillets and spacing creates a parquet floor with enough
stability to permit installation with minimum expansion.
Acrylic Impregnated Wood is
More Stable
Acrylic impregnation marries the
properties of wood with the plastic technology developed in the early 50's.
Using the absorption ability of wood, two chemicals in solution are forced
into the dry wood fibers completely saturating the wood. An outside force is
then used to combine the two chemicals (polymerize) into solid acrylic
(plastic). This chemical reaction takes place throughout the thickness of the
wood. The resulting wood floor product has increased density, hardness, ( see HARDNESS Table of Wood Floor Species ) and wear
resistance; and coloration can be inserted uniformly through the thickness of
the wood. The acrylic fills the fibers and deters moisture absorption, thereby
providing increased dimensional stability. These floors do not require
"refinishing," in the pure sense of the word, since the acrylic
finish is throughout the thickness. Surface treatment performed occasionally
will reveal a brand new floor!
Up to this point the properties
discussed have pertained only to solid oak floors, one piece of wood through
its thickness. Hold on, because now we're going to take those properties and
use them as we change direction entirely.
Laminated Floor Blocks are Warp
Resistant
Laminated floor products came into
being in the 50's as the result of improved peeling and gluing technology.
Again using the property of oak's tangential expansion, three layers of oak
are glued together with the face (top) layer and back (bottom) layer grain
running parallel or the same direction. The center (core) layer is turned 90°
during assembly and the glue used in the assembly is stronger than the wood
itself. Now, as the fibers in each layer absorb moisture and want to expand,
each layer is restrained by the other and improved dimensional stability
results. There are many laminated floors that have performed successfully,
even when cut tight to walls. 
Production of the laminated
products begins with the felling of the tree, but after stripping off the
branches, the trunk remains whole, rather than cut into logs as with solid
flooring. The tree length logs are transported directly to the flooring mill
and dumped into water filled ponds or stacked under constant sprinkling to
keep them as wet as possible. The logs are then placed in huge vats filled
with hot water and live steam and literally cooked for at least 24 hours.
After removal from the vat, the full length tree is cut into bolts of varying
lengths determined by the characteristics of the log and the mill's need for
backs and faces or cores. The bolt is positioned in a large lathe and turned
at high speed against a sharp blade that literally unrolls the log just as a
roll of toilet tissue unrolls. The cooking of the log turns the fibers into
(almost) a wet box of Kleenex, making this peeling operation possible. 
Because the peeling requires
soaking wet logs, no prior drying is required. This fact makes it possible for
laminated products to respond quickly to increases in demand. The utilization
of the log is greater since nearly the entire volume of wood is used. The
high-quality portion for face layers, lower quality for cores and backs. The
sheets of veneer pass through a dryer, are clipped for defect and size, glued
and assembled into plywood sheets, generally about 48" x 60". It is
conceivable that a tree is felled in the woods on Monday and is plywood by
Thursday. The large plywood sheet then is ripped and diced up to produce a
myriad of laminated
(engineered) floor products and Prefinished floors .
There are several variations on
the theme. The usual is three layers, however, some manufacturers use five.
Oak cores are common, but other species are acceptable. Backs are normally oak
but species of very similar characteristics are sometimes used. The bottom
line, however, is always the same. An odd number of layers with the face and
back of the same (or similar) species produces a dimensionally improved,
warp-resisting floor product.
Laminated Blocks Installed
Below Grade
Ultimately, the customer has for
their floor, a product that displays far less expansion and contraction with
moisture changes and therefore can be successfully installed below grade, in
basements, in humid climates, and even fit tight to vertical obstructions.
Very different from solid floors. The floor can be glued direct to concrete
with several adhesive types. There is a visual difference between laminated
and solid flooring that many customers will be unable to discern; as the log
is peeled it opens up a grain flair that is much more pronounced than that
found in a sawed product.
The width of the bands of
springwood/summerwood is greater and the stain acceptance and less wear
ability of the springwood is apparent.
The major concern of many who
display resistance to the laminated products is longevity. Can a laminated
floor be sanded and refinished? Consider the thickness of the top layer. The
thicker the better. Some products entering the market in the late 80's have a
very thin face veneer, and are doubtful as to their ability to be sanded and
refinished. The entire life wear and appearance of the floor is in the face
thickness. The thick-faced products, with proper maintenance,
can be expected to last up to 20 years' end can be sanded and refinished at
least twice by a pro, giving another 40 years. A 60-year floor! Yes, we do
have something to sell.
Another variation of laminated
flooring has come to our country from Europe and doubtless will soon be
manufactured within our shores. The face is many pieces -- or one piece -- of
sawn wood, not peeled veneer. The core is solid pine (or other species)
fillets aligned across the width of the plank. The back is a peeled veneer
with grain direction parallel to the face. This flooring is non-beveled and
prefinished, and very salable in our market today.
And another variation -- an
impregnated sawn oak multi-piece thin face, with a separated oak fillet core
at 90° grain direction -- with no back -- for adhesive installation.
See Related Pages:
Hardness Table
for Wood Floor Species
Wood Floors
+ Water = Trouble
Wood
Flooring Cuts & Grades
Wood
Flooring Species
