M-P
Matching of Burls, Crotches, & Stumps:
These wood figures need special treatment when being matched into faces because of there generally exotic grains. Burls and crotches have a tendency to be buckled. When making a panel face it is usually necessary to flatten and patch the veneer. They also have a tendency to develop fine hairline splits, so must be carefully handled in manufacturing. This extra labor usually adds to the expense of using these grains, however the results are well worth the cost.
Mediums:
Shakes produced with a thickness of 1/2 to 3/4 inch.
Microllam:
Laminated Veneer Lumber (LVL). High strength beams produced from stress graded veneers. Manufactured in 1-3/4" thick billets with grain parallel to primary load axis. For high load, long span applications.
Moisture Content:
The weight of the water in wood expressed as the percentage of the weight of the oven-dry wood.
Mottle:
A term applied to figured wood that gives the impression of an uneven surface, although smooth. Broken wavy patches across the face. Twisted interwoven grain with irregular cross figure, which is the mottle. The effect is due to reflected light on the uneven arrangement of the fibers. The value of cabinet wood is increased greatly when it is mottled.
Nominal Size:
The size designation for most lumber, plywood, and other panel products, used for convenience. In lumber, the nominal size is usually greater than actual dimension; thus, a kiln dried 2x4 ordinarily is surfaced to 1-1/2x3-1/2. In panel products, the size is generally stated in feet for surface dimensions and increments of 1/16-inch for thickness. Product standards permit various tolerances for the latter, varying according to the type and nominal thickness of the panel.
Open Knots:
Opening produced when a portion of the wood substance of a knot has dropped out, or where cross checks have occurred to produce an opening.
Overlaid Plywood:
Plywood with a surfacing material added to one or both sides. The material usually provides a protective or decorative characteristic to the side, or a base for finishing. Materials used for overlays include resin-treated fiber, resin film, impregnated paper, plastics, and metal.
Parallam:
Parallel Strand Lumber (PSL). A composite wood product where veneers are clipped into 1" strips and pressed together (all grain parallel) into a large billet. Billets are cut into different sizes for high strength beam and column applications. The attractive material may be left exposed. CCA treated PSL is also available for exterior use.
Particle Board:
A panel composed of small particles of wood and wood fiber that are bonded together with synthetic resin adhesives in the presence of heat and pressure.
Pecky:
These are areas, or pockets, of disintegrated wood caused by localized decay, or wood areas with abrupt color change related to localized injury such as bird peck. Peck is sometimes considered as a decorative effect such as bird peck in pecan and hickory or pecks in cypress.
Pentachlorophenol (Penta):
A chemical used in wood preserving; it is usually applied under pressure so that it will penetrate the wood.
Pin Knot:
A knot with a diameter no larger than 1/2 inch.
Pitch:
1. An accumulation of resin in the wood cells in a more or less irregular patch. Classified for grading purposes as light, medium, heavy, or massed. 2. The angle or inclination of a roof, which varies according to climate and roofing materials used. 3. The set, or projection, of teeth on alternate sides of a saw to provide clearance for its body.
Plywood:
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.
Pressure Treating:
A process of impregnating lumber or other wood products with various chemicals, such as preservatives and fire retardants, by forcing the chemicals into the structure of the wood using high pressure.