Plywood is an engineered product and considered a general construction material as it is used for sheathing, subfloors and various applications in construction. Plywood is constructed from two thin sheets of softwood, hardwood or a combination of both with a sandwiched layer of wood chips running vertical to the grain of the top and bottom layers. The chips are glued and the sheet is baked at high temperatures to create a strong sheet. Three layers, or plys, are standard but extra layers may be added to create a stronger sheet. Plywood is tested for tensile strength, can be treated for fire and water resistance. Produced in 4X8 foot sheets.
• Structural plywood is used where strength is needed such as flooring.
• External plywood is not used for structural purposes and has a finished panel and is used for wall cladding, or exterior door panels.
• Internal plywood is not used for structural purposes, has a finely finished top panel and is used for walls and ceilings.
• Marine plywood is treated with preservatives, paint or varnish so it won’t delaminate.
• Grades of plywood run from A, B, C, D, or N. N has very few and little knots or defects in graining while D may have many of these. A, B, and C will range from few to a few more. C-D is interior rated with a top sheet with few defects and a D undersheet that may have more so. Also, the adhesive used is appropriate for interior use.