OPTIONS FOR THE WINDOW TREATMENT INDUSTRY.
Many window treatments are
mounted on lumber instead of decorative or functional poles and rods. Therefore,
it is important to understand lumber and some of its characteristics in order
to choose the best wood for each product.
The lumber used in constructing
window treatments is the same softwood lumber used in general construction.
It is referred to as Dimensional Lumber, or lumber that is from one inch up
to, but not including, five inches thick and that is two or more inches in width.
Dimension also is classified as framing, joists, planks, rafters, etc. These
are primarily cut from the evergreen families of pine, spruce and fir.
There are many many different
types and grades of lumber. For our purposes, this article will concentrate
on the type, sizes and grades which are optimal choices for the window treatment
industry in terms of price and functionality. This article also compares the
quality and suitability of different flat panel options which are used for framing
arched treatments and for the faces of cornice boards.
LUMBER IS CUT, MILLED
& GRADED FOR QUALITY:
Trees are cut and the
rounded sides are cut off, creating a square trunk. From the square trunks,
planks are rough cut in nominal sizes of 1x4. 1x6, 2x4, etc. The nominal
designation of the plank is the label by which it is sold.
The milling process
trims and smooths the rough planks down to dimensional sizes (actual sizes)
which are sold to the end user. The milling process takes a nominal 1x4
and mills it to a dimensional 3/4" x 3.5".
The lumber is then graded
on its quality. The grading process is complicated and based on a set of
criteria by which to judge various pieces of lumber or panels in terms of
strength and appearance. Regional grading agencies draw up rules for grading
based on the voluntary product standards issued by the U.S. Bureau of Standards.
Strength: A measurement
of strength in lumber involves the basic properties of wood: fiber stress
in bending, tension parallel to grain, horizontal shear, compression perpendicular
to grain, and elasticity.
Knots also affect the
strength of a plank. They are formed by a branch or limb embedded in a tree
and cut through in the process of manufacturing. Knots are classified according
to size, occurance and tight/loose (loose knots fall out, leaving a hole
in the wood). Knots can be a problem in that they are more dense than the
surrounding wood, making it difficult to staple into and/or will more readily
split when a screw is inserted.
size and number of knots also affects the clean appearance of the board.
However, dust boards and legs are covered with lining and/or fabric, hiding
the knots. Appearance is also judged by the number and size of other imperfections:
splits, gouges, etc.
CHOOSING THE RIGHT LUMBER
FOR THE JOB.
Pine is the best choice
for all window treatments. It is relatively inexpensive, yet durable and easy
to work with. To choose lumber for a job, first select the grade most appropriate
for the job, then examine the wood for warping and imperfections.
#2 grade -
- Has some knots, usually
small to medium in size.
- Minor imperfections
- Dried to a range of
less than 19% humidity. Stable in areas of normal ranges of humidity.
- Least cost of three
grades discussed here.
- Suitable for most standard
dust boards and legs.
#1 grade -
- Has fewer knots, usually
- Few imperfections.
- Dried to a range of
less than 19% humidity.
- Stronger than #2 grade
- Slightly more expensive.
- Suitable for treatments
where extra long boards and/or wider boards are required. Also recommended
for treatments of considerable weight. Basically, you would choose this
grade because of its additional strength.
Clear grade -
- Free of knots and imperfections.
- Probably dried to 6-8%
humidity range. Most stable in humid conditions
- Decidedly more expensive
than #1 grade.
- This is furniture grade
lumber. It is no stronger than the previous grade. The higher price is for
appearance only. Since dustboards and legs are covered with fabric, the
appearance would not be a factor and this grade of wood would be excessive
for most window treatments.
Examine the board to ensure
it is clean and free of dirt, gouges, splits and large or loose knots. Also
check for black mold. This form of mold is known to cause deadly illness in
small infants and people with weak immune systems. A board with black mold
should never be used in a window treatment.
Test for warpage. Ideally,
the board should lay flat on the floor on all four sides. A board which bows
front to back cannot be used for a window treatment as it needs to be flat
againt the wall. A board which bows in a U shape can be straightened at the
time of the install using extra "L" brackets. The severity of the
bow will determine whether or not it is suitable for the job.
If you stockpile lumber
for future jobs, storage is an important issue.
Lumber is best laid flat
on a supported surface which does not allow the center to bow. If you must
stand it up, prop it securely against the wall in a manner in which it is
supported and does not bow.
Storage area must be relatively
dry and clean. Do not store in a dark, damp area which will encourage the
growth of mold.
Always purchase the longest
boards you can store easily. In this way, you can cut long dust boards from
full size boards and smaller boards from the scraps, thereby optimizing your
FLAT PANELS FOR CORNICES
& FRAMING ARCHES
Cornice boards are constructed
using dimensional lumber for the dustboard and sides. A panel product is used
for the face. Frames for arched windows or unusually shaped window treatments
also use panel products because they come in larger sizes and are easy to cut
to a specific shape.
The three most commonly
considered panel products for cornices are oriented strand board (OSB), particle
board and plywood. All come in standard sheets of 4' x 8' and in a variety of
Oriented Strand Board
An offshoot of wafer
board, OSB is a structural panel made of narrow strands of fiber oriented
lengthwise and crosswise in layers, with a resin binder. OSB's strength
comes mainly from the uninterrupted wood fiber, interweaving of the long
strands or wafers and degree of orientation of strands in the surface layers.
Waterproof and boil proof resin binders are combined with the strands to
provide internal strength, rigidity and moisture resistance.
Because OSB is constructed
of small pieces of wood glued together, screws and staples do not always
hold securely and could tend to pull out if enough tension is applied. Also,
because it is often used in exterior construction, arsenic and/or rat poison
are sometimes added to the OSB mix to discourage rodents from chewing on
it. While OSB is an inexpensive alternative, its use should be limited in
the window treatment industry.
Particle board, another
form of composition board, is made by binding wood particles ranging in
size from flakes to sawdust together with a suitable adhesive, such as a
plastic resin, and pressing or extruding them to form sheets. Particle board
is used as a cheaper substitute for plywood in some applications.
Because of its higher
density, particle board is less resistant to puncture. It is considerably
heavier than the other choices and very difficult to staple into. Its weight
and density make it difficult to use in the window treatment industry.
Plywood is a flat panel
made up of a number of thin sheets, or veneers, of wood in which the grain
direction of each ply, or layer, is at right angles to the one adjacent
to it. The veneer sheets are united, under pressure, by a bonding agent.
This panel product cuts
easily and screws stay secure. Plywood is probably the best choice for cornice
faces. It is easy to cut and handle and is stable under humid conditions.
For most window treatment
applications, 1/2" to 5/8" thick plywood is best. Small cornices
could use 3/8" thick plywood, but larger cornices will be more stable
with thicker measures. It is not necessary to purchase plywood thicker than
5/8" because the construction of cornices and arch frames is such that
the panel piece will be supported and stable. Thicker plywood would simply
make the treatment heavier and more cumbersome.
Plywood comes in three
Unfinished on both
sides. Both surfaces of the plywood are rough and gouged. The holes would
have to be filled with wood putty and sanded smooth before the plywood
could be used for a window treatment. Least cost of three choices.
Finished on one side.
One surface of the plywood is unfinished. The other surface is usually
a layer of oak or birch which is sanded smooth and has no holes. Higher
cost than unfinished.
Finished on both sides.
Both surfaces of the plywood are finished with a layer of oak or birch
and sanded smooth. Most expensive of the three alternatives.
It is the workroom's
discretion whether to use unfinished or finished plywood. The smooth surfaces
of the finished plywood will contribute to a finer finished product with
less time and effort spent trying to fill in or hide the roughness of the
Return to the Sew Easy Windows articles Table of Contents page.