Plywood
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Toy constructed from plywood. Notice the high quality wood veneer (light color) covering the lower quality inner wood (dark color). |
Plywood was the first type of
engineered wood to be invented. It is made from thin sheets of
wood veneer, called plies or veneers, which are stacked together with the direction of each ply's grain differing from its neighbors by 90° (cross-banding)
[O'Halloran, M.R. 1989. Plywood. In Concise Encyclopedia of Wood and Wood-based Materials, ed. Arno Schniewind. Oxford: Pergamon. p. 221-226.]. The plies are bonded under heat and pressure with strong
adhesives, usually
phenol formaldehyde resin[Handbook of Finnish Plywood, Finnish Forest Industries Federation, 2002, ISBN 952-9506-63-5], making plywood a type of
composite material. A common reason for using plywood instead of plain wood is its resistance to shrinkage, twisting and warping.
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A wall lamp made partially from plywood |
A vast number of varieties of plywood exist, tailored for all manner of conditions and uses.
Softwood plywood is usually made either of
Douglas fir or
spruce,
pine, and
fir, and is typically used for construction and industrial purposes
[O'Halloran, p.221.]. Decorative plywood is usually faced with
hardwood, including
red oak,
birch,
maple,
lauan (Philippine
mahogany) and a large number of other hardwoods.
Plywood meant for indoor use generally uses the less expensive phenol formaldehyde glue (which has limited water resistance), while outdoor and marine grade plywood are designed to withstand rot and use a water resistant phenol-resorcinol glue to prevent
delamination and retain strength in high
humidity.
The most common varieties of softwood plywood comes in three, five or seven plies with dimensions of 1.2 m × 2.4 m (4 feet × 8 feet). Each ply is 1/8 inch. Roofing can use the thinnest 3/8-inch plywood. Floorboards are at least 5/8-inch depending on the distance between floor joists. Plywood is often
tongue and grooved for flooring applications. Two of the edges will have
"grooves" notched into them to fit with the adjacent "tongue" that protrudes from the next board.
High-strength plywood, known as
airplane plywood is made from birch. It was used for several
WWII fighter aircraft.
Airplane plywood was adapted for furniture by
Alvar Aalto.
Plywood production requires a good log, called a peeler, generally straighter and larger in diameter than that required for processing by a
sawmill. The log is peeled into sheets of veneer which are then cut to the desired dimensions, dried, patched and glued together to form the plywood
panel. The panel can then be patched, resized, sanded or otherwise refinished, depending on the market it was intended to be sold in.
Plywood has been made for thousands of years; the earliest known occurrence of plywood was in
ancient Egypt around 3500 BC when wooden articles were made from sawn veneers glued together crosswise. This was originally done due to a shortage of fine wood; thin sheets of high-quality wood were glued over a substrate of lower-quality wood for cosmetic effect, with the structural benefits arising only incidentally. This manner of inventing plywood has occurred repeatedly throughout history; for example, many of the great English furniture makers such as Sheridan used veneer as a raw material.
Modern plywood in which the veneer are cut on a rotary
lathe from softwood logs is of relatively recent origin, invented by
Immanuel Nobel (the father of the more-famous
Alfred Nobel). The first such lathes were set up in the
United States in the mid
19th century. Plywood has been one of the most ubiquitous building products for decades.
Compare to OSB (
Oriented strand board) and MDF (
Medium-density fibreboard).
*
Engineered wood*
Fiberboard*
Glued laminated timber*
Hardboard*
Masonite*
Marine plywood*
Medium-density fiberboard*
Oriented strand board*
Particle board*
Pressed wood*
The Engineering Wood Association (formerly known as the American Plywood Association)* Sellers, Terry. 1985.
Plywood and Adhesive Technology. New York: Dekker. ISBN 0824774078
