Pressure treated timber

Pressure treated timber

1.What is vacuum pressure impregnated wood?


Vacuum pressure impregnated wood is wood that, through the application of a preservative, is protected for many years against fungi and insects. To achieve this effect, wood is put in a closed horizontal cylinder Ð the autoclave Ð and then the air is drawn out of the cylinder and out of the wood cells. Then the preservative is admitted and the content of the treatment cylinder is put under pressure. By doing this, the preservative enters deep into the wood cells. After this, the vacuum is sucked again to make sure that any excess preservative is completely removed. The process is brought to an end by a fixation treatment to ensure that the applied preservative will remain in the wood by entering into a chemical reaction with the wood.


2. Why should wood be impregnated?


Wood is a renewable and natural material, which is continuously available, thanks to sustainable forest management. But it is also susceptible to attacks by fungi, micro-organisms and insects. In particular in contact with soil and water, wood is quickly affected and rots in most cases in a matter of years. Attacks by fungi also quickly occur in other places where wood is exposed to moisture. There are only a few wood species that, by nature, are very resistant against rot and attacks by insects. These species are mostly tropical hardwoods and very expensive. Other species must be protected before they can be used for a long time. By being impregnated the timber is given a service life many times longer than that of untreated timber, while the additional treatment costs are low, particularly when compared to the generally high costs of maintenance and replacement of untreated timber. Some preservation treatments allow for a use of several decades.


3. How durable is wood naturally?


The natural durability of wood depends very much on the wood species, the relation between the components sapwood and heartwood, the age of the tree from which the wood is cut and the circumstances in which the wood is used. These factors are always variable while preserved wood provides the certainty of long use in a wide array of applications. Untreated sapwood is never durable.


4. How is timber impregnated with the preservatives?


The impregnation industry has highly technical plants in which the timber to be treated is impregnated by using vacuum pressure cycles to achieve the required absorption and depth of penetration.


5. How do impregnation plants operate?


Timber impregnation plants operate in a closed circuit. The plants are protected by bunds of appropriate capacity in relation to their size. The plant operators receive thorough training in operating the plants and in handling the wood preservatives as well as the newly impregnated timber. After completion of the impregnation process the timber remains at specially prepared sites within the plant until fixation of the preservatives has been achieved. 


6. Can all wood species be preserved in the same way?


No. Due to biological differences between wood species, there are differences in the degrees in which preservatives can be brought into the wood. 

For example, preservative does not enter more than a few millimetres into spruce, while the sapwood of larch, pine, Douglas and European oak is penetrable up to the core. This does not constitute a problem as long as the wood is not damaged or cracked by drying or "working". In this case, the untreated sapwood becomes available as feeding ground for fungi. The working of wood is limited by thorough drying, construction and/or painting. Sometimes incising is used to ease the tension in the wood and to enable deeper penetration. (In using incising, small grafts are made in the wood with a knife roll). 


7. How to choose a wood preservative?


To be effective, a wood preservative must possess the following properties:

toxicity towards wood-destroying organisms

ability to penetrate deeply into wood

permanence in the treated wood

it must not have damaging effects on the wood itself

it must be non-corrosive to metals

it must not damage the health of those involved in its manufacture, transport or use in the impregnation plants, or any buyers or consumers of impregnated timber.

All European countries have regulations and reliable procedures for assessing and evaluating the afore-mentioned properties. Approval of the wood preservative is not given until all relevant examinations by the proper authorities have been concluded satisfactorily. The European Biocidal Products Directive will provide a global system for approvals throughout the European Union.


8. Is preserved wood safe for the environment?


Yes. If used properly, timber impregnated according to definitive regulations with officially approved preservatives does not constitute a danger to man, animal or plant-life. Concerned questions from researchers, ENGOÕs and government authorities have always resulted in a continuous search for means, methods and preserved wood products. Research covers everything, including the waste phase. All these studies confirm time and again that preserved wood is safe for man and his environment.


9. Where do I use preserved wood?


Impregnated timber is used for:

electricity and telephone poles

railway sleepers, crossings and bridge timbers

industrial cooling towers

snow fences

landing stages, jetties and lake and sea embankments

palisades and fences

stakes for fruit and wine-growing

playground equipment, carports and pergolas

noise barriers

pavement blocks

constructional timber and joinery

and any purpose for which timber is exposed to the effects of the weather.



10. Can children play safely on playground equipment made of preserved wood?


Several studies have concluded that there is no danger in playing on preserved wooden playground equipment. Playing in preserved wooden sand pits is also completely safe. There is no danger of leaching of the applied preservative, even by licking the wood.


11. Is preserved wood safe in vegetable patches and gardens?


Yes. Preserved wood is ideal for putting in borders, sawing boxes, cases, mushroom boxes, rose structures, pergolaÕs, compost boxes, beanstalk, etc. There is no risk of damaging plants or of plants taking up components of preservatives from the wood.


12. Does preserved wood cause health risks for humans?


If used properly and for the intended use, preserved wood does not cause health risks for humans. 

Epidemiological research spread over many years with workers at wood preservation companies and woodworkers have shown that illnesses, including cancer, are no more or less prevalent than with professions that have no connection with preserved wood.



13. Should vacuum and pressure treated wood be painted?


No. That is not necessary. Preserved wood is maintenance free. However, there is an aesthetic aspect too. After a while, unpainted, preserved wood will change colour under influence of the ultra-violet in the sunrays. The speed with which this happens depends on the place where the wood is used and the preservation process. For wood preserved with salts, there are various products on the market. Many finishing products can be obtained from garden centres and paint stores, to give preserved wood the colour of your choice. The only quality demand is that the wood must be dry before painting.



14. What to do with waste wood?


The nature of preserved wood waste is determined by the type of wood preservative used. It should never be burnt in household stoves or on open fires but be delivered to a waste collection unit. This will ensure its correct destruction. Through incineration, the energy content of wood is again usefully employed for the generation of electricity. Advanced smoke purification techniques have ensured that there is no longer any detrimental effect of also incinerating of old wood. There is no influence on the composition of the ashes and its recycling possibilities. Preserved wood, like painted or glued wood, should not be burned in an open fire.