Introduction to Preservative Treatments

Timber is an organic product and in the presence of sufficient moisture and air will be attacked by fungus, causing decay. Preservative treatments can be introduced into the cellular structure of timber to protect it from fungi and insects. Preservative treatments may also include fire retardant chemicals. These are frequently applied to linings, joinery and cladding.

Preservative treatment of timber generally protects only the sapwood. All sapwood is non-durable if not preservative treated. Heartwood cannot be effectively treated with most preservatives as heartwood cells contain resins and other extractives that retard the uptake of preservative solution. The sapwood of all major plantation softwood species and some hardwoods can be effectively treated with timber preservatives.

The major timber preservatives currently used in Australia are:

• Boron Salts
• Light Organic Solvent Preservatives (LOSP)
• Copper Chrome Arsenate (CCA)
• Creosote
• Copper Azole
• Ammonium Copper Quaternary (ACQ)

Reference: Timber Datafile P4 – Timber – Design for Durability of the NAFI Timber Manual.

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Timber Research Unit
Department of Architecture
University of Tasmania