PLGN 5.07 Plywood Joinery

The outer layers of plywood exposed to weather are prone to develop fine surface cracks (`checks`) running parallel to the grain, even when painted.

Checking varies in severity according to the species of timber used for the outer veneer it is less severe, for example, with African Mahogany and Gaboon, whilst Douglas Fir ( Columbian Pine) and Finnish Birch are prone to severe checking. Checking effects only the surface layer of the outer veneer but, if the surface is painted, the cracks are communicated to the coating, allowing entry of moisture and failure of paint system. Plywood is available with a resin-impregnated paper overlay which prevents checking and provides a satisfactory base for painting; the use of this type of material is recommended for external use where a paint finish is required, especially with species prone to severe checking.