Veneer and Knots
The veneer peeled from logs may contain characteristics such as knots or splits. The size of knots and splits are controlled by grading into categories of different qualities. Knotty plywood can be used for many applications. Knots can be removed and replaced with wood or synthetic patches to enhance appearance. To obtain veneer with no knots, more expensive pruned logs are peeled.
The glues used to bond the veneers together are synthetic phenolic resins, which are set and cured by heat and pressure under controlled conditions to form a strong and durable bond. Plywood can be used for applications requiring strength, stiffness and durability, and may be specified for its aesthetic qualities or because of its origins within a renewable resource. The choice of products depends on the application.
If treated, structural plywood is generally impregnated to H3 Hazard class with CCA (Copper Chrome Arsenic) treatment to AS/NZS 1604.3:2002. H3 CCA treated plywood in accordance with AS/NZS 1604.3:2002 is comparable to H3.2 and H3 LOSP is comparable to H3.1.
H3 hazard class is described as: “outside, above ground, subject to periodic, moderate wetting and leaching.” Refer to the Standard for more detail.
CCA waterborne preservative is used for structural plywood. It has a green colour, and is dried following treatment so that the sheets may return to the correct dimensions and are moisture content suited to use in building. The fillets used to separate sheets in drying may leave marks on the sheet surface. These fade after a time, and are easily covered with paint but may be visible under stain.
The process of treating with CCA and subsequent drying is likely to increase the face checking of the panel. Refer CHH Woodproducts Technical Note 01/06/62 “CCA plywood – surface quality.”
Structural Product Information