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WEI Questions & Answers

  1. What is vacuum pressure impregnated wood?
  2. Why should wood be impregnated?
  3. How durable is wood naturally?
  4. How is wood impregnated with the preservatives?
  5. How do impregnation plants operate?
  6. Can all wood species be preserved in the same way?
  7. How to choose a wood preservative?
  8. Is preserved wood safe for the environment?
  9. Where do I use preserved wood?
  10. Can food and water come into contact with preserved wood?
  11. Can children safely play on playground equipment made of preserved wood?
  12. Is preserved wood safe in vegetable patches and gardens?
  13. Does preserved wood cause health risks for humans?
  14. Are there any additional precautions for working with preserved wood?
  15. Should vacuum and pressure treated wood be painted?
  16. What is creosoting?
  17. How is the safety of wood preservation companies assured?
  18. What do scientific studies say about the safety of vacuum pressure impregnated wood?
  19. Why is preserved wood in many instances an ideal substitute for concrete, plastics, steel and aluminium?
  20. What to do with waste wood?

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). The fact that heartwood is generally difficult to impregnate does not necessarily constitute a problem due to longer natural durability.

7. How to choose a wood preservative?

The chemical composition of wood preservatives is dependent upon the intended subsequent use of the impregnated timber and upon the biological hazards to which it will be exposed. These criteria are taken into account in selecting the various chemicals and in determining the proportions in which they are used.
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 timer 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 food and water come into contact with preserved wood?

For reasons of hygiene, it is not recommended to prepare food on a treated wood surface. Pick-nicking on a preserved wooden table, however, is not a problem. Preserved wood can also be used safely in contact with water if it is treated with a preservative that is allowed for this use.

11. 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.

12. 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.

13. 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.

14. Are there any additional precautions for working with preserved wood?

The usual precautions for the use of building materials must be respected. The use of gloves, eye protection and dust mask must be standard practice in the sawing, drilling, shaving, sanding and gluing of all kinds of building materials, including preserved wood. Use rust free attachment materials such as nails and screws. Otherwise, it is possible for wood to be in good condition while the attachment materials have already rusted.

15. 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.

16. What is creosoting?

Creosoting is the process of vacuum and pressure impregnation of wood with creosote oil. Creosote oil is a quality preservative made from the distillation from coal tar. The coal tar itself is released from the coal during the coking process as it is done for the high oven production of steel. Creosote oil is used in railway sleepers, embankments, fence posts and telephone poles. The preserved wood is clean and does not leach. Creosoted wood in the waste phase is a good fuel with a high burning value that does not leave behind rests.

17. How is the safety of wood preservation companies assured?

Wood preservation companies are specialised companies that know wood and chemicals very well. They are very aware that it is of the utmost importance to work carefully. This is in the interest of their employees, the surrounding area and the buyers of their products. This professional care is apparent in the following instances:
  • The preservation takes place in a closed system where nobody comes into contact with the preservative (because it is brought straight from the tanker or container into the installation);
  • A highly automated process control which ensures that not more or less preservative than necessary is brought into the wood);
  • The preservation installation is placed in a liquid proof safety basin so that in case of an accident, there are no consequences for the surrounding are or the soil;
  • Waste water is continuously re-used in the preservation process;
  • Personnel is well trained and knows the emergency procedures;
  • Wood is delivered only after the preservative is fixed sufficiently naturally or artificially.
  • Companies work with a valid environmental licence.
18. What do scientific studies say about the safety of vacuum pressure impregnated wood?

Several studies at home and abroad have demonstrated the following:
  • Preserved wood has a longer use-life than untreated wood and contributes in a significant way to the preservation of the natural resource: the forest;
  • Preservatives do not or hardly leach to the soil or the water and preserved wood does not have adverse effects on aquatic life;
  • Using preservation and preserved wood correctly does not cause a risk for cancer or other illnesses in humans and animals;
  • Preserved wood products have been tested comprehensively and were found to be very reliable. They cost less energy than the same products of other materials and are aesthetically sound and usually fit nature and landscape better.
19. Why is preserved wood in many instances an ideal substitute for concrete, plastics, steel and aluminium?

Except that wood is the only naturally renewable resource, (re-produced sustainably through good forest management), it is also the least energy intensive building material. Other materials require much more energy to turn the raw material Ð oil or mineral Ð into a basic product. The further processing to a finished product is not as energy intensive for wood as for the other materials. The environmental impact of the forestry and woodworking industry is many times smaller than other industries. Wood has a very high strength to weight ratio. It also has a high material stiffness that makes strengthening unnecessary, and it is also sufficiently resilient. Wood is relatively cheap and easier to work by the DIY person, and available in countless species and sizes. It is almost insensitive to changes in temperature and feels warm, even in winter. Wood furthermore has a high resistance to chemical attack, making it ideal for e.g. the storage of road salt and material for manure silos.

20. 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.