Timber Treatment and Hazard Levels

Approx read time: 2 minutes

The durability and service life of timber products can be enhanced by impregnating the cells with stable preservatives that act to repel wood destroying insects (such as termites, white ants and borers), and breaking down fungi spores that lead to wood rot.

The impregnation process can vary depending on the timber species, preservatives, carrier agents and treatment hazard level – but can include dipping, spraying or vacuuming the carrier agent into the timber substrate in a high-pressure environment.

Timber treatments are primarily focused on protecting the sapwood. The sapwood of all species is considered non-durable (because of its life-supporting starches and sugars) and is comparatively easily penetrated by preservatives. It is not possible to effectively treat the heartwood of many timber species, as heartwood cells contain extractives that prevent the uptake of preservatives.

Treatment Types

LOSP (Light Organic Solvent Preservative) is commonly used in high-value joinery and products treated in their final form and dimensions. LOSP treatments can only be used in above ground applications, providing up to Hazard Level 3 (H3). The active preservatives can include tributyl tin naphthenate (TBTN), azoles and synthetic pyrethroids.

ACQ (Alkaline Copper Quaternary) contains copper and a quaternary ammonium compound. Its colour can range from dark to brownish green, and it is applied using a pressure process as a water-borne preservative. It is free of arsenic and can provide up to Hazard Level 4 (H4). It can be painted or stained when dry.

Copper Azole is one of a new generation of preservative treatments that can be used in water-borne pressure treatment processes. It is a preservative that contains copper, boric acid and tebuconazole and is commonly used with softwood species as an arsenic-free alternative to CCA for treatments up to Hazard Level 4 (H4). It is odourless and can be stained or painted when finished.

CCA (Copper, Chromium and Arsenic) impregnates the timber with water and salts under pressure. Offering a high level of resistance to leaching, CCA can be used on timber exposed to the elements or used in-ground. It is free of odour but has a green appearance which may detract from its appearance. The Australian Pesticides and Veterinary Chemical Authority (APVMA) requires that CCA treated timber may not be used for public projects, children’s playgrounds, garden furniture, picnic tables, external seating, domestic decking or handrails.

In Australia, the use of framing treated for termite resistance is becoming a standard practice for builders who want to offer their customers peace-of-mind. In outdoor environments, Australian grown plantation pine can be cost efficiently treated and used as a sustainable alternative to imported exotic hardwood for many common projects – including carports, pergolas, decking structures and playgrounds. Timber treatments can also significantly enhance the lifespan of timber used in in-ground applications – such as garden walls and landscaping projects.
However, treatments do not provide protection against the effects of weathering. All timber used in outdoor environments should be protected with the application and maintenance of a suitable coating system.

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