Plywood

Plywood was the first type of engineered wood to be invented. It is made from thin sheets of wood veneer, called plies, which are stacked together with the direction of each ply's grain differing from its neighbors by 90° (cross-banding). The plies are bonded under heat and pressure with strong adhesives, usually phenol formaldehyde resin1, making plywood a type of composite material.

Related Topics:
Engineered wood - Veneer - Adhesive - Phenol formaldehyde resin - 1 - Composite material

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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. Decorative plywood is usually faced with hardwood, including red oak, birch, maple, lauan (Philippine mahogany) and a large number of other hardwoods.

Related Topics:
Softwood - Douglas fir - Spruce - Pine - Fir - Red oak - Birch - Maple - Lauan - Mahogany

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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.

Related Topics:
Glue - Delamination - Humidity

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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.

Related Topics:
Sawmill - Panel

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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.

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A common reason for using plywood instead of plain wood is because plywood is more stable and because it is less prone to change (shrink, twist or warp).

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