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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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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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