The outer layers of plywood are known's the face . The face is the surface that is to be used or seen. The center layer is known as the core. In plywoods with five or more plies, the inter-mediate layers are known as the crossbands.Plywood may be made from hardwoods, softwoods, or a combination of the two. Some common hardwoods include ash, maple, mahogany, oak, and teak.
Composite plywood has a core made of particleboard or solid lumber pieces joined edge to edge. It is finished with a plywood Veneer face . Composite plywood is used where very thick sheets are needed.The most common softwood used to make plywood is popular wood, available in india, although several varieties of eucalyptus, and redwood are also used.
The type of Resin used to bond the layers of wood together depends on the specific application for the finished plywood. Softwood plywood sheets designed for installation on the exterior of a structure usually use a phenol-formaldehyde resin as an adhesive because of its excellent strength and resistance to moisture. although most softwood interior sheets are now made with the same phenol-formaldehyde resin used for exterior sheets. Hardwood plywood used for interior applications and in the construction of furniture usually is made with a urea-formaldehyde resin.
Some applications require plywood sheets that have a thin layer of plastic, metal, or resin-impregnated paper or fabric bonded to either the face to give the outer surface additional resistance to moisture and abrasion or to improve its paint-holding properties. Such plywood is called overlaid plywood and is commonly used in the construction, transportation, and agricultural industries.
Other plywood sheets may be coated with a liquid stain to give the surfaces a finished appearance, or may be treated with various chemicals to improve the plywood's flame resistance or resistance to decay.