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Timber Treatment.

HISTORY

Timber preservation in Australia commenced in the 1930`s using simple dip treatments of boron and arsenic to prevent insect attack in susceptible building timbers. Major expansion of the timber preservation industry occurred in the 1960`s with the introduction of pressure preservation plants and legislated standards for timber treatment. The 1980`s saw the emergence in usage of plantation softwoods and the introduction of more sophisticated treatment plant automation. In the 1990`s and beyond, emphasis has been placed on improved environmental management of new and existing treatment plants.

NATURAL DURABILITY

The heartwood of all timbers can be classified according to its natural durability(or resistance) against attack by wood destroying organisms such as termites, borers and decay fungi. The resistance is due to the presence of special tannins, oils, resins and extractives in the heartwood that repel or kill insects and decay.

There are four classifications of natural durability with examples for each shown below. It is important to note that natural durability refers only to mature outer heartwood. Sapwood of all timbers is considered non durable with Radiata Pine having a low natural durability. When treated with Copper- Chrome- Arsenic (CCA) preservative Radiata Pine performs as good or better than a durability class 1 timber.

> NATURAL DURABILITY

CLASS 1

Timbers of the highest natural durability which may be expected to resist both decay and termite attack for at least 25 years and up to 50 years

Grey Box
Grey Ironbark
Red Ironbark
Yellow Box
Tallowwood

CLASS 2

Timbers of high natural durability which may be expected to have a life of about 15 to 25 years

Jarrah
River Red Gum
Spotted Gum
White Cypress Pine

CLASS 3

Timbers of moderate durability which may be expected to have a life of about 8 to 15 years

Southern Blue Gum
Brush Box
Manna Gum
Candle bark

CLASS 4

Timber of low durability which may last about 1 to 8 years

Douglas Fir(Oregon)
Radiata Pine
Western Red Cedar
Slash Pine

 

CCA PRESERVATIVES

The Copper-Chrome - Arsenic (CCA) preservatives enjoy world-wide use and offer a broad spectrum of activity against timber destroying organisms.

Each of the chemicals in CCA plays a specific and important role in the preservation of timber. Arsenic is an insecticide that deters and kills insects such as termites and borers. Copper acts as a fungicide to minimize attack by fungi such as brown rot, dry rot, soft rot and white rot. Chromium is a fixing agent that ensures arsenic and copper are bound to the wood structure during its service life.

TIMBER TREATMENT PROCESS

Timber treatment processes have been designed to ensure that the preservatives penetrate the timber structure and provide protection during the desired service life.
As sapwood is more permeable to preservatives than heartwood and sapwood is more susceptible to degrade than heartwood, treatment processes have generally been designed to treat sapwood.

Portland Pine Products utilize a modern and fully automated plant, following a proven vacuum-pressure impregnation process to ensure the most consistent results are achieved. In particular the Full Cell process, also referred to as the Bethell process ,has proven to be the most cost effective and consistent method by which to pressure impregnate timber with waterbourne CCA solutions over the various Hazard Classes (refer below table) designated in the Australian Standards.( AS1604)

Prior to treatment the roundwood product is air dried to a moisture content range between 25-28% to facilitate the uptake of CCA solution. The expected absorption of solution into the timber is typically between 400-600 litres/m3.

There are five distinct stages of the treatment process:
Initial vacuum-air is removed from the sapwood cells( to assist in preservation solution impregnation)
Flooding-the initial vacuum is maintained whilst preservative solution is run into the treatment vessel until full. About 80% of preservative retention is attained during flooding.
Pressure period-after flooding, the vacuum is released and pressure is applied. The pressure is maintained until the solution flow rate is negligible (treating to refusal) or for a set period of time determined by practical experience.
Kickback and emptying-upon release of pressure, some solution (kickback) is forced out of the timber due to the expansion of compressed air within the wood cell walls. The cylinder is drained and solution is returned to the storage tanks.
Final vacuum-a final vacuum is applied to remove excess solution and prevent dripping from the surface of the treated timber when removed from the treatment vessel.

TREATMENT HAZARD CLASSES

H1 - Inside, above ground, dry
Insect borer (other than termites) hazard. Framing, flooring, furniture etc

H2 - Inside, above ground, dry
Insect borer and termite hazard. Framing, flooring, trusses

H3 - Outside, above ground
Moderate fungal decay and termite hazard. Decking, fencing, cladding, fascia, window joinery, exterior structural timber

H4 - Outside, in ground
High fungal decay and termite hazard. Fencing, greenhouses, pergolas, non-structural and landscaping timbers

H5 - Outside, in ground or fresh water
High fungal decay and termite hazard. Engineered retaining walls, building poles, pilings, and cooling tower fill, structural or critical applications

H6 - Marine water exposure
Marine borers hazard. Marine piles, jetty crossbracing, landing steps, sea walls

PROCUCT LABELLING

To comply with Australian Standards, treated timber should be labeled on one end as per this example (jpeg file).

The first 3 digits (525) will uniquely identify the producer, that is, Portland Pine Products.
The next two digits (01) identifies the preservative used to treat the timber, and in this case the 01 code represents CCA.
The final two digits of the label beginning with the letter 'H' identifies what treatment hazard class the timber has been treated to.

SAFE HANDLING AND DISPOSAL

Only use treated timber that is clean, dry and free of surface residues. Do not inhale wood dust and wear a filter mask while sawing, machining and sanding or any operation where wood dust is generated. Protect your eyes whilst working with tools or any work where small particles might be ejected. Wash sawdust off skin and clothes. Wash hands after work and before eating, drinking or smoking. Wash clothes and equipment before re-use.
DO NOT BURN treated timber, off-cuts or waste pieces. Domestic and trade users should dispose of sawdust, off-cuts and redundant pieces through normal waste disposal services in compliance with local authority requirements.
Do not use treated wood for composting, mulching or animal bedding.


MSDS

Click here to view Portland Pine Products MSDS - pdf file

SERVICE LIFE

The service life of treated timber depends on a variety factors including the level of preservative treatment and the range of conditions and type of environment anticipated during the service life of the timber.

Where subsequent machining, shaping, pointing, and cutting of treated timber are unavoidable, supplementary protection should be applied to the cut surface. This protection cannot be expected to be as effective as the original treatment hence the reason why Portland Pine Products offer an extensive range of sizes , lengths, finishes and pointed options to choose from.