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Know all About Lumber & Plywood
Choosing
Lumber
A clean, fresh, uncut board says "carpentry" like no
other material. And indeed, lumber is the starting point for almost all
carpentry projects. But the landslide of lum ber sizes, species, and
grades awaiting the uninitiated can be overwhelming at first. Armed with
an understanding of some basic terms, you can usually secure friendly help
with the fine points. Of course, if you're just building some simple
garage shelves or patching a hole in the backyard fence, you can probably
close your eyes and buy a couple of boards. But for anything larger, you
should do a little homework first.
Lumberyard Lingo
For starters, you'll need to know how
lumber is categorized by type and size. Here are some passwords:
Hardwood or Softwood?
Lumber is divided into hardwoods
and softwoods, terms that refer to the origin of the wood: hardwoods come
from deciduous trees, softwoods from conifers. The terms can be
misleading. Though hardwoods are usually harder than softwoods, some
softwoods- like Douglas fir and southern pine- are actually harder than so
called hardwoods such as poplar, aspen, or Philippine mahogany (lauan).
As a rule, softwoods are much less expensive, easier to tool, and more
readily available than hardwoods. In fact, nearly all facets of house
construction today are done with softwoods. The durable, handsomely
grained hardwoods are generally reserved for fine interior paneling,
flooring, and other finish work.
Lumber Classifications
The softwood sawmills that
subscribe to grading services cut trees into products that fall into five
categories.
- Dimension lumber is the stuff of wood framed houses. It is 2" to 4"
thick, 2" wide and up and is graded for strength rather than appearance.
Graders look for knots, checks, slope of grain and other defects that
can affect the wood's strength.
- Boards or commons are typically used for siding or shelving, and
they are graded for appearance rather than strength. This class of
material comes out of the center of the tree and will have plenty of
knots.
- Beams, posts and timbers measure at least 5" by 5". they are usually
taken from near the center of the tree, and are used to carry heavy
loads in all types of construction. Strength is of utmost importance;
there are cosmetic grades for exposed structures.
- Shop lumber can be of any thickness or width. it is cut near the
heart - between the selects and the commons - where large expanses of
clear wood are interrupted by the occasional large knot. Shop material
is purchased mainly by outfits called remanufacturing plants. They rip
the stock to useable widths, cut out the knots and use the clear pieces
for highly tooled products like window frames and moldings. Finger
jointed jambs started out as shop grade.
- Selects and finish lumber come from the outer layers of the log.
They are graded for appearance and are virtually free of knots and pitch
pockets. Fancy moldings and cabinets are made from these cuts.
Plywood
Cheaper and lighter than most solid
wood, plywood is strong and flexible and thus ideal for such applications
as furniture and cabinetry, sheathing, paneling, and boat building.
Plywood is made of very thin layers of wood (called plies, or veneers)
that are aligned and glued together. Generally, the middle layer, or core,
is veneer, lumber, or manufactured wood. The outer plies (called face and
back) are usually better appearance quality wood than the interior ones.
Face is better than back.
Veneer-Core Plywood
The strongest type is made up of
an odd (or occasionally even) number of plies. Three, five, seven, and
nine plies are common compositions. Veneer-core plywood is generally
available in thicknesses up to 1 1/8". The plies are layered with the
grain of each running at right angles to those of neighboring plies; this
arrangement locks the grain, preventing the panel from shrinking
widthwise. It also gives it strength in all directions and minimizes the
distortion caused by warping and shrinkage. The plies are bonded with
interior or exterior glue.
Although the grains of one ply are at right angles to those of another,
the panel itself does have an overall grain running lengthwise. It is this
grain direction that provides the panel with the greatest strength. When
installing a panel , run its grain horizontal to the joists or studs.
Lumber-Core Plywood
Lumber-core Plywood is made in the
same way as veneer- core except, of course, for the core, which is strips
of solid lumber. It comes in thicknesses up to 1". The edges of
lumber-core plywood holds screws securely. Plywood is further divided into
two basic kinds: construction and hardwood. Construction plywood, which is
primarily softwood, is available in 4x8 foot panels; its common
thicknesses are ¼, ½, and ¾". Hardwood plywood, used mainly for decorative
purposes, comes in panels 4x7, 4x8, or 4x10 feet; thicknesses range from
1/8 to 3/4". Construction plywood is rated by the way it performs (span
rating), regardless of thickness. Span rating refers to the maximum space
( in inches) needed between supports to effectively support a panel. Most
panels have one rating; sheathing has two ( roof / floor). Plywood in
lumberyards and home centers must meet the standard of the American
Plywood Association (APA). You can special order thicker panels and higher
grade face veneers.
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