Treating Timber

While many timber species are naturally durable and resistant to insect attack and decay, the major species of timber used commercially in New Zealand and to a wide degree in Australia, Radiata Pine, does not possess the natural durability required to meet Building Code requirements or consumer expectations in some cases.  As a result Radiata Pine requires preservative treatment to enable it to achieve desired levels of durability.

Fortunately Radiata Pine is very easily treated.  Due to its cell structure, it is the most treatable species of timber in the world.

Well treated Radiata Pine will perform to the durability performance requirements of building legislation in New Zealand and in Australia.

The standard of treatment of timber is laid down in NZS 3640:2003.  The treatment standard for reconstituted wood products (e.g. particle board), plywood, laminated veneer timber and glue laminated products are specified in AS/NZS  1604 Parts 2 to 5 respectively.

In general, treatment standards set out the requirements for penetration of preservatives into the wood and retention of a given level of preservative for each hazard class.  The higher the level of risk or hazard class the greater the level of retention required. 

Treatment processes vary from preservative to preservative.  Pressure treatments are used for CCA, ACQ and Copper Azole which are water based.  Lower pressure treatments are used for solvent based preservatives TBTN, TBTO, propiconazole + tebuconazole, IPBC and Copper Naphthenate.  Lower pressure processes are also used for new boron formulations.  Other new boron formulations are applied by spray or dip.  Traditional boric diffusion involves a dip process.

All WOODmark licensed treatment plants are required to operate in compliance with health and safety and environmental protection standards.  These are described in the Best Practice Guideline for the Safe Use of Timber Preservatives & Antisapstain Chemicals. Most treatment plants have to be operated under the supervision of a HSNO Approved Handler.

Testing treatment quality

The WOODmark programme requires licensed treaters to conduct internal testing of their products at a frequency specified in the Timber Preservation Quality Manual.

WOODmark auditors undertake independent testing of licensees’ production four times a year. In most cases spot testing using reagents is conducted.  At other times samples are sent to an accredited laboratory where tests are conducted in accordance with established protocols and standards.