Engineering and Construction

Structural wood panel products fall into three general categories (Figure 3.29): Plywood panels are made up of thin layers of wood  veneer glued together. The grain on the front and  back face veneers runs in the long direction of the sheet, whereas the grain  in one or more interior crossbands  runs perpendicular, in the shorter direction. There is always an odd  number of layers in plywood, which  equalizes the effects of moisture movement, but an interior layer may  be made up of a single veneer or of  two veneers with their grains running  in the same direction. Composite panels have two parallel face veneers bonded to a core of reconstituted wood fibers. Nonveneered panels are of several  different types:

Oriented strand board (OSB) is made of long shreds (strands) of wood  compressed and glued into three to five layers. The strands are oriented  in the same manner in each layer  as the grains of the veneer layers in  plywood. Because of the length and  controlled orientation of the strands,  OSB is generally stronger and stiffer  than the other types of nonveneered panels. Because it can be produced  from small trees and even branches,  OSB is generally more economical than plywood. It is the material  most commonly used for sheathing  and sub flooring of light frame wood buildings. OSB is also sometimes  called waferboard, a name that applies  more precisely to a similar type of  panel made of large flakes of wood  that has been largely replaced by  OSB.

Particleboard is manufactured in different density ranges, and is made up  of smaller wood particles than OSB  or waferboard that are compressed and bonded into panels. It  finds use  in buildings mainly as a base material  for wood veneer and plastic laminate.



It is also used commonly as an under- layment panel to create an especially  smooth substrate for the application  of resilient flooring.

Fiberboard is a very fine-grained  board made of wood fibers  and  synthetic resin binders intended for  interior uses only. The processing of  the raw wood products in fiberboard  manufacturing is more intensive  than that in the manufacture of particleboard, resulting in a panel that  is dimensionally more stable, stiffer, better able to hold fasteners, and  superior in its working and finishing  characteristics. The most commonly  used form of fiberboard  is  medium- density fi  berboard (MDF). It is used in  the production of cabinets, furniture,  moldings, paneling, and many other  manufactured products. Though the  names are similar, care should be taken not to confuse MDF panels with  medium-density overlay (MDO) ply- wood panels, discussed below.

Figure 3.29 Five different wood panel products, from top to bottom: plywood, composite panel, waferboard, OSB, and particle- board.