The many types and grades of plywood.

The invention of plywood can be one of the most signifficant development in the technology of woodworking. This is one form of a wood product that makes it very useful and versatile to the woodworker.

Plywood is a flat panel built up of sheets of veneer called plies, put together under extreme pressure by glue to create a panel with an adhesive bond between the plies. Plywood can be made from either hardwoods or softwoods.The outside plies are are called faces or face and back plies; the inner plies are called centers or cores; and the plies with the grain perpendicular or a right angle to that of the face are called crossbands. Crossbands gives the panel strength and keep the grain of the panels from running all in the same direction.

With having grain running in both directions the plywood can have equal strength in its width and length. Plywood will also be less prone to splitting, checking, and warping and its dimensional quality will have a high rating also.

In general there are two classes of plywood available,(a) Constuction and industrial, (b) Hardwood and decorative. The first type (a) has traditionally been made from softwoods such as Southern Pine, white fir, western hemlock, douglas-fir and redwood. A large number of hardwood qualify under the current standard for use also, but the standard for hardwood and decorative plywood covers certain decorative softwood species for nonconstruction use only.

Most of the constuction and industrial plwood that is used in the United States is produced domestically with some of the manufacturers exporting some materials. The majority of constuction and industrial plywood is used where stiffness and strength and construction codes are more important than the appearance of the plywood. There are some grades of this plywood that are made with the face of the plywood selected just for the appearance and generally used with clear natural finishes or with stain finishes.

Hardwood and decorative plywood can be made of many different species, both in the United States and abroad. United States imports a large amount of panels that are used in this country. Hardwood plywood is use in applications such as decorative wall panels and in the cabinet and furniture industry where appearance is a important factor.

These are some examples of various types of panels but the pictures of the panels does not give the actual appearance justice. The best way to view the various panels is to go to your local home improvement store or lumber yard to see first hand the differences in each of these panels.

Oriented Strandboard also known as OSB can be used for roof sheathing, underlayment, subfloors, single-layer floors, exterior siding, and wall sheathing. These panels are free of knotholes and will securely hold screws and nails. Some of the grades available are siding, sheathing, and single floor with sizes available in 4' x 8' sheets and thickness that range from 3/8' and up.

Particleboard is a hard and dense composition board that has small particles of wood that has been glued together with various types of adhesive under extreme pressure and heat. Mainly used in non-structual constuction such as closets, and because it will not warp it makes a good underlayment also. It does have a tenancy to swell if it gets wet

Hardboardis made from chips of wood that has been machined down to wood fibers and then adhered together into thin panels under heat and pressure. These panels are also dense, strong, grainless, and very dry. Some of the uses of these panels are perforated boards, interior paneling, cabinets, toys and much more. Warping can occur if it is used in areas where high temperature and humidity exists.

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