Timber Treatment


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.


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.

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
CLASS 2 Timbers of high natural durability which may be expected to have a life of
about 15 to 25 years
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


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 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.

Jelfor Timbers uses proven vacuum-pressure impregnation processes to ensure the most consistent results are achieved. The Full Cell (Bethel) process has been proven to be the most cost effective and consistent method by which to pressure impregnate timber with water borne CCA solution over the various Hazard Classes.

There are five distinct stages of the Full Cell (Bethel) 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.

The Alternating Pressure Method (APM) is used to treat partially seasoned (steamed) timber. This method allows rapid treatment of green timber and avoids costly seasoning.

There are three distinct stages of the Alternating Pressure Method (APM) treatment process:

  • Initial Vacuum – there is little to no initial vacuum required in APM schedules. Instead the work tank should be topped up to maximum and the cylinder flooded via gravity. If the cylinder cannot be fully flooded then a vacuum of no more than -20kPa should be applied. There will not be much absorption of the solution by the timber at this stage, so the sight gauge on the work tank should stabilise before the pressure cycle starts.
  • Pressure – the pressure phase should consist of approximately 10-15 cycles as follows,
    (a) Raise pressure to 1400kPa ± 50kPa then hold pressure for 2 minutes
    (b) Release pressure suddenly to 0kPa and hold for 1 minute
  • Final Vacuum – after a blow-back or pump-back of the solution to the work tank, a final vacuum of -85kPa should be applied for a minimum of 15 minutes. There should be quite a large release of liquid so a final blow-back should be required also.


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


To comply with Australian Standards, treated timber should be labelled on one end.

The first 3 digits (519) will uniquely identify the producer, that is, Jelfor Timbers.
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.


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.


The service life of treated timber depends on a variety of factors including the level of preservative treatment and the specific application of the product (refer to treatment hazard classes).

The range of conditions and the type of environment anticipated during the service life of the product can vary based on climate, geographic location and seasonal changes. In consideration of service life, if subsequent machining, shaping, pointing cutting and scarfing of treated timber posts and poles are unavoidable, supplementary protection should be applied to the cut surface. This protection however cannot be expected to be as effective as the original treatment application. If actions are undertaken that compromise the integrity and treatment application of the product, Jelfor Timbers will not be responsible for subsequent issues arising from such actions and any warranties shall be considered null and void by any further processing of treated products.

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