It is necessary to design realistically for them, in both engineering and architectural applications if consistently good performance is to be achieved. Some processed forms of wood are of interest in the context of these discussions. Wood can be broken down by pulping or chipping and reconstituted into sheets in numerous ways as represented by paper, fibreboards and chipboards of various kinds. The strength and the dimensional change properties in the different directions of the sheet or board are altered in ways that are generally quite consistent with the nature of the fibre reorientation achieved. Changes in thickness may be much greater, approximating those in the original cross-grain direction.
Plywood is one of the more interesting forms of processed wood.
Plywood for general use must always be of balanced construction. Briefly, this means that each veneer on one side of a sheet must always be balanced by one of equal properties and equal orientation on the other side. unless this is done, serious warping will take place when the moisture content changes. This directional effect is progressively reduced as the number of plies is increased. Shear properties in the plane of the sheet are always greatly improved because of the reinforcement given by adjacent plies against tension failure across the grain. The improvement in dimensional stability is marked, since the superior stability and modulus of elasticity along the grain provide an enhanced restraint for the cross-grain dimensional change.