How durable is untreated wood?
The natural durability of untreated wood depends very much on the wood species, the relation between the main components of the 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 can be used for a long time in a wide array of applications. Untreated sapwood is never durable.
Why use wood preservatives?
Wood is a renewable and natural material, continuously available through sustainable forest management. But it is also susceptible to fungi, micro-organisms and insects. In particular, wood that is in contact with soil and water is quickly affected and decays in just a few years. Attacks by fungi also quickly occur in other places where wood is exposed to moisture. There are only a few wood species that are resistant to decay and insects. These species are mostly tropical hardwoods and very expensive. Other species must be protected before they can be used for a long time. Once treated, the timber can last many times longer than untreated timber, and additional treatment costs are low, particularly when compared to the cost of maintaining and replacing untreated timber. Some preservation treatments allow wood to be used for several decades.
How does one choose a wood preservative?
The chemical composition of wood preservatives is dependent upon how the treated timber will be used, and upon the biological hazards it will face. The NTR system guides the user in selecting the the correct NTR use class.
To be effective, a wood preservative must have/be:
- Toxicity towards wood-destroying organisms
- Ability to penetrate deeply into wood
- Permanence in the treated wood
- No damaging effects on the wood itself
- Non-corrosive to metals
- Harmless to those involved in its manufacture, transport or treatment process plants, as well as to any buyers or consumers of impregnated timber.
All European countries have regulations and reliable procedures for assessing and evaluating the aforementioned 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 Regulation provides a rigid control for approvals throughout the European Union.
How is timber impregnated with preservatives?
Strictly regulated timber treatment plants impregnate timber using vacuum pressure cycles to achieve the required absorption and depth of penetration.
How do timber treatment plants operate?
Timber treatment plants operate in a closed loop, protected by moisture bunds of appropriate capacity. The plant operators are highly trained 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 the timber is ‘drip free’. The plants are designed to recycle the extra preservative back to the chemical storage area.
What is vacuum-pressure-impregnated wood?
The process of treating vacuum pressure-impregnated wood involves the wood being put into a closed horizontal cylinder (the autoclave) and then the air is drawn out of the cylinder and out of the wood cells. Then the preservative is let in and the content of the treatment cylinder is put under pressure. By doing this, the preservative soaks deep into the wood cells. After this, the vacuum is sucked again to ensure that any excess preservative is completely removed. The final part of the process, the chemical reaction of the preservative with the wood cells locks the applied preservative into the wood. Through this process the wood is protected for many years to come against fungi and insects.
Can all wood species be preserved 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 Fir and European Oak penetrates 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 a feeding ground for fungi. The working of wood is limited by thorough drying, construction and/or painting. Sometimes incising – making small grafts in the wood with a knife roll – is used to ease the tension in the wood and to enable deeper penetration. The fact that heartwood is generally difficult to impregnate does not necessarily constitute a problem due to its longer natural durability.
Is preserved wood environmentally-friendly?
If used properly, timber impregnated according to definitive regulations with officially approved preservatives does not constitute a danger to humans, animals or plant life. Researchers, environmental NGOs and government authorities have spurred continuous improvements in the processes of preserving wood products, including the waste phase. All these studies confirm time and again that preserved wood is safe for humans and the environment. Recent life-cycle assessments have determined that treated wood has a much lower environmental risk than alternative materials such as concrete, steel and plastics.
Where can 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 growing and vineyards
- Playground equipment, carports and pergolas
- Noise barriers
- Pavement blocks
- Construction timber and joinery, and any purpose for which timber is exposed to the effects of the weather.
Can food and water come into contact with preserved wood?
For hygiene reasons, it is not recommended to prepare food on a treated wood surface. However, picknicking on a preserved wooden table 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.
Can children play 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 the applied preservative leaching out, even if the wood is licked.
Is preserved wood safe in vegetable patches and gardens?
Yes. Preserved wood is ideal for putting in the likes of borders, sawing boxes, cases, mushroom boxes, rose structures, pergolas, compost boxes and beanstalks. There is no risk of damaging plants or of plants absorbing components of preservatives from the wood.
Does preserved wood cause health risks for humans?
If used properly as intended, preserved wood does not cause health risks for humans.
Epidemiological research over many years into the health of woodworkers and workers at wood preservation companies have shown that illnesses, including cancer, are no more or less prevalent than with professions that have no connection to preserved wood.
Are there any additional precautions for working with preserved wood?
The usual precautions for the use of building materials must be respected. Gloves, eye protection and dust masks must be used in the sawing, drilling, shaving, sanding and glueing 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 corroded.
Should treated wood be painted?
It is not necessary. Preserved wood is maintenance free. However, there is an aesthetic aspect too. After a while, unpainted, preserved wood will change colour through exposure to ultra-violet rays from the sun. 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 bought 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.
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 of coal tar. The coal tar itself is released from the coal during the coking process, just as it is in the oven production of steel. Creosote oil is used in railway sleepers, embankments, fence posts and utility poles. The preserved wood is clean and offers extended service life upwards of 60 years in ground contact. Creosoted wood in the waste phase is a good fuel, with a high burning value that does not leave anything behind.
How do we know wood preservation companies are safe?
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 ensures that no 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 area or soil;
- Wastewater is continuously re-used in the preservation process;
- Personnel are well trained and know the emergency procedures;
- Wood is delivered only after the preservative is fixed sufficiently naturally or artificially.
- Companies work with a valid environmental licence.
Why is preserved wood often an ideal substitute for concrete, plastics, steel and aluminium?
Wood is the only naturally renewable resource, re-produced sustainably through good forest management. But it is also the least energy-intensive building material. Other materials require much more energy to turn the raw material (oil or mineral) into a basic product. The further processing to a finished product is not as energy-intensive for wood as it is 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 with, and available in countless species and sizes. It is almost insensitive to changes in temperature and feels warm, even in winter. Wood also has a high resistance to chemical attack, making it ideal, for example, the storage of road salt and material for manure silos.
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.
Most new produced treated wood is not classified as hazardous waste as is the case with old scrap wood.
Preserved wood, like painted or glued wood, should not be burned in an open fire.