EWPAA Structural Plywood and LVL Design Manual - Engineered ...

Borers are rarely a problem with structural plywood or LVL except in the marine environment. The mainland borers which attack seasoned timbers are the lyctid borers, which only attack the sapwood ofsome hardwoods, and the anobium borer which attacks both softwoods and hardwoods and is mostcommonly a problem in old furniture. In New South Wales and Queensland, lyctid susceptible hardwoodproducts, from which a purchaser might reasonably expect a long life, must by law be treated againstlyctid borers.Marine borers found in marine waters, can be highly destructive of timber products. It is advisable tocheck with local marine authorities to determine the hazard level in any particular area. Some marine borersbore holes in the wood for shelter rather than food and do not digest the wood, making it difficult to protectthe wood through chemical treatment. Other marine borers such as the Teredo borers, digest the woodthrough which they tunnel and chemical preservative treatments are effective in protecting the timber.Marine borer damage to a hardwood pylonPreservative TreatmentsPreservative treatment types and preservative retention levels for treatment of structural plywood andstructural LVL are specified in Australian Standard AS/NZS 1604.3 Specification for preservative treatment,Part 3: Plywood and AS/NZS 1604.4 Specification for preservative treatment Part 4: Laminated VeneerLumber (LVL).AS/NZS 1604.3 and AS/NZS 1604.4 describe six hazard level classifications, denoted by a hazard numberform H1 to H6 as shown in TABLE 16.13. Each hazard level is defined in terms of the expected serviceexposure. H6 is the most severe hazard level. Where preservative treatment is required for plywood orLVL, the appropriate standard and hazard level should be specified. It should be noted that there are severaldifferent methods of incorporating preservative treatment into plywood and LVL products. Preservativetreatment methods for plywood and LVL include:• impregnation of veneers prior to manufacture,• a glueline preservative additive during manufacture,• pressure treating of the finished product,• preservative treating surfaces after manufacture.Veneer preservative treatments preservative treat each individual veneer prior to manufacture and nofurther treatment will be required if the plywood or LVL is cut.A glueline additive is a preservative added to the adhesive prior to bonding of the individual veneers.The flow of moisture from the glueline into the individual veneers during the hot press phase ofmanufacture, carries the preservative into the individual veneers ensuring each individual veneer ispreservative treated. Face veneers have only one associated glueline and thicker face veneers may requireadditional preservative treatment, which is typically achieved in the manufacturing process by spraying faceveneers as the product exits the hot press.Pressure treatment of the finished plywood or LVL results in an “envelope” type treatment. The outerveneers and ends of the sheet or beam will have been preservative treated but the preservative may nothave penetrated through the gluelines to the inner veneers. If the plywood or LVL is cut after preservativetreating, a paint or preservative treatment should be applied to the cut edge. Where possible, pressurepreservative treatment of the finished product should be done after any machining, sawing and boring.255