Limitations of Use

This section provides information on limitations of use.

The Preservative Standard NZS 3640:2003 is applicable only to products as they leave the treatment plant site.

Through the implementation of appropriate quality assurance and quality control procedures, producers take reasonable care to ensure the treated products meet the minimum requirements of the treatment standard.

They are assisted by  third party independent quality assurance organisations which audit their procedures,

Subsequent care and handling of preservative treated products during transport, storage, sale, installation, use and on-going maintenance are covered by guidelines and recommendations by suppliers and/or producers.

The Preservative Standard NZS 3640:2003 only covers the chemical treatments to give durability from biological agents. 

Some supplementary information is provided in that standard and in the Timber Use Standard NZS 3602:2003.

The Preservative Standard NZS 3640:2003 does not cover all fitness for purpose requirements needed to meet the broader definition for durability in the Building Code.

Information on other durability requirements necessary to demonstrate ‘fitness for purpose’ can be sourced from industry organisations or suppliers.

Some specific examples:

• Framing timber treated with a water-soluble preservative (boron) needs to be protected from prolonged exposure to the weather.  This can be achieved by an impervious wrapping of packets or by storage of treated timber indoors.  During the construction phase framing is inevitably exposed to the weather. Intermittent rainfall over a normal period of exposure to weather during construction (~3 months) will pose few problems,

• Machining and sawing timber after treatment can reduce the effectiveness of treatments and it is recommended to check with preservative suppliers whether  a supplementary protection needs to be applied to the cut/machined surface(s).

• Sawn treated timber should not be planed or machined and products such as decking should be purchased treated in ‘final shape and form’ dimensions. Because of the high costs associated with disposal of treated shavings, treatment in final shape and form of such products is now the norm. Preservative suppliers may also require the fresh cut ends to be protected with a supplementary  treatment as part of their warranty conditions.

• Treated timber should only be used for the designated hazard class; each piece of timber has the hazard class number in the brand identification. As an example square sawn timber treated to hazard class 4 is not a substitute for square sawn hazard class 5 piles.

• Timber products treated with water-based preservatives or copper-based preservative systems need to be allowed to dry before installing fixings or fasteners. Application of grease to bolts which pass through CCA-treated timber (e.g. building poles) as added protection against corrosion is often recommended, but not a substitute for the correct metal fastener type such as hot dipped galvanised or stainless steel.

• The cut ends of any pole or pile should not be put into the ground even after a supplementary treatment has been applied to the cut surface.