INDUSTRIAL TIMBER BUILDING MATERIALS PRESERVATION
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© BWPDA May 03
Wood and timber is a superb material and the only truly sustainable resource and building supply for construction. Plantation grown softwood timbers from certified sources are most widely used in construction but such timber lacks sufficient natural durability for many situations. However, the correct treatment of timber, in conjunction with good building design and maintenance will deliver exceptional performance for any application.
Industrial wood and timber preservation technology is the process by which stable chemical solutions are safely introduced into the structure of the wood / timber to prevent fungal decay and wood insect attack. Timber treatment takes place in purpose designed plant under strictly controlled conditions and is a technology which permits selection of the pre-treatment process of timber and preservative most appropriate to the timber component’s end use (eg. Used in Timber cabins, timber fences, log cabins, timber poles, raw timber as building materials, timber dog kennels, timber stairways and balustrades, floor boards, pergolas and timber arches, and timber trellises).
TIMBER
Timber and wood is the oldest and most attractive of man’s building supplies and materials. Light yet strong and easily worked, timber is an infinitely versatile material with a natural beauty and warmth unmatched by any other construction product or building material. As a raw material, timber has the added advantage of being one of the few renewable resources and with proper forestry management the equilibrium between growth regrowth of timber, and commercial utilisation can be maintained. However, long term forestry strategies and world economic cycles rarely coincide, therefore any action that would lead demand for timber to outstrip production of timber and further deplete the world’s forest resources must be avoided. Timber preservation has major importance in contributing to the conservation of these resources, ensuring that wood and timber is used sparingly and to its full potential and life span.
THE ADVANTAGES OF PRE-TREATMENT OF TIMBER
Most of the timber species currently used in the UK are low in natural durability and vulnerable to attack by destructive biological organisms like wood destroying fungi and insects. Such organisms compromise the structural integrity of the timber and subsequently lead to its premature failure. The consequences for safety and the cost of repair, rebuilding or timber replacement can be considerable.
Good timber building design and timber maintenance are essential but alone they cannot always protect untreated timber. To ensure a long, safe and useful life, timber needs preservation, and pre-treatment is the most effective and economical means of achieving this. This is because timber pre-treatment processes are carefully controlled.
Impregnation techniques in which the amount of preservation required is tailored precisely to the timber components end use and the characteristics of the species from which it is made. The fact that large amounts of timber components can be treated at the same time also brings economies of scale to the process making it highly cost effective.
TIMBER AND FIRE
As well as preventing biological degradation of timber, pre-treatment technology is equally effective and economical in providing the means to improve the performance of timber in the event of fire. By making ignition of timber more difficult and reducing the rate at which flame spreads across timber, fire retardants play an important role in the protection of human life. Specialist advice on fire retardant treatment of timber is to be found in the Wood Protection Association Manual.
TYPES OF WOOD AND TIMBER PRESERVATIVE AND METHODS OF APPLICATION
Timber pre-treatment is carried out in purpose designed industrial plants that impregnate the structure of the wood or timber, with a preservative solution using a carefully controlled process.
The type of preservative used together with its strength and method of application are determined by the type of timber component, its risk of exposure to biological attack during its desired service life and the characteristics of the species used. Besides its efficiency against organisms, a good industrial timber preservative must also possess other properties. It should penetrate the wood without causing damage and have an appropriate effective life without affecting the performance of appropriate metal Fittings and fixings incorporated into the use of timber as a building material. Above all it must not affect the health of anyone involved in its proper manufacture, transport and application or any user of the treated timber article.
In order to achieve the correct level of timber treatment it is important to adhere to recognised official standards set out for timber and building with timber as a building material. These define the desired results of timber treatment and divide end uses of timber into classes according to the type of hazard they are likely to meet in service life of that timber.
Timber Hazard Class
1 Internal, with no risk of wetting
2 Internal, with risk of wetting
3 External, above damp proof course
4 In permanent contact with the ground or fresh water
5 In permanent contact with sea water
The Wood and Timber Protection Association Manual provides detailed advice on the selection and specification of preservative treatment of timber products.
There are four main types of wood and timber preservative used for industrial pre-treatment: Organic Solvent
Waterborne — Low pressure
Waterborne— High pressure
Creosote
WATERBORNE (Low pressure)
This type of timber preservative contains small quantities of fungicide and/or insecticide dissolved in water. This forms the bulk of the product. Dyes may be added to the timber preservative if so desired. The treatment is quick-drying and is typically used for general construction and building purposes falling into Hazard Classes 1, 2 and 3. These preservatives are applied to timber components in an enclosed treatment vessel using either double vacuum process cycles or a vacuum/low pressure process to achieve the required absorption and depth of penetration. The treated timber can be glued, overpainted or stained.
WATERBORNE (High pressure)
Waterborne formulations are the most widely used wood and timber preservatives in the world today. They provide protection against wood-attacking organisms in all situations and are applied using vacuum and high pressure process cycles to maximise penetration of the timber. They are odourless and after impregnation combine with the wood / timber becoming resistant to leaching. It is possible to add dyes or water repellents during the treatment process of timber, and once dry; timber can be glued, painted or stained.
CREOSOTE
This type of timber preservative is obtained by the distillation of coal tar and is impregnated into timber under vacuum and pressure using either a full or empty cell process. In full cell treatment the aim is to retain the largest possible amount of creosote in the wood / timber. The empty cell process leaves the cell walls coated as opposed to filling the entire cell space. Creosoted timber components have been examined after 100 years service life. The timber was sound and the efficiency of the creosote when extracted and tested was found to be excellent. This high degree of permanence, even in salt water, makes creosote ideal for treating external structures, transmission poles, railway sleepers and timbers categorised as Hazard Class 4 & 5. There are many applications where timber preservatives are interchangeable and a choice can be made. A number of variable factors can influence this choice and the Wood and Timber Protection Association is able to offer free and impartial advice on the most suitable form of treatment for any timber product in any situation.
ORGANIC SOLVENT FOR TIMBER PRODUCTS
Similar in application to low pressure waterborne types of timber treatment, but use white spirit instead of water as a carrier. Most often used in the treatment of timbers covered by Hazard Classes 1, 2, & 3. Because organic timber solvent preservatives are readily absorbed and do not affect the surface of the timber and characteristics of a timber component, they are highly suitable for the treatment of machined joinery timber products installed above d.p.c level where there is low to medium risk of decay.
PRE-TREATED TIMBER AND THE ENVIRONMENT
For safety, value and versatility, pre-treated timber is the ideal construction and building material. Yet, along with the practical benefits of timber products, its use also has considerable environmental importance making possible the continued utilisation of timber with the lasting care of the world’s forest resources.
By making timber and wood last longer in service, pre-treatment of timber effectively reduces the total number of trees that need to be felled to meet timber supplies demand. It also enables the use of many species of timber which might otherwise be considered unsuitable as building material thus taking the pressure off more valuable and ecologically important resources. For example, inexpensive pre-treated softwoods from the sustainable forests of temperate latitudes can be used where previously only a particularly durable hardwood or more expensive non-timber alternative would have been acceptable.
Moreover, the conversion of timber into a readily useable and durable pre-treated commodity and building material and supplies makes far fewer demands upon the environment than man-made building materials and supplies like steel, aluminium, concrete and pvc which consume finite raw building materials and precious energy in their production.
It should also be added that timber components treated with an approved wood / timber preservative to regulated procedures do not in themselves constitute a danger to man, plants or animals.
From the economic, technical and environmental perspective, pre-treated timber has much to commend it.
SETTING STANDARDS FOR TIMBER PRODUCTS AND BUILDING SUPPLIES
The Wood and Timber Protection Association and its members recognise the importance of safety and that the use of timber and wood preservatives needs to be regulated and carried out in well designed plant by properly trained operatives who have responsible and environmentally aware attitudes toward timber manufacturing and use as building materials. In support of these principles all wood and timber preservatives must be approved under the Control of Pesticides Regulations; timber treatment plants should conform with the WPA Code of practice for safe design and operation of timber products; plant operators should receive formal training in procedures regarding timber products, and be assessed to ensure their competence in handling process equipment, chemicals and treated timber. The WPA and its members take a responsible stance in addressing the requirements of new legislation and regulatory bodies.
The Wood Protection Association (a Division of BWPDA)
The Wood and Timber Protection Association encompasses BWPDA members who treat timber in industrial treatment plants, manufacturers and suppliers of timber preservatives and timber fire retardants and Associate members including universities, colleges, research organisations, other associations and trade bodies in the UK and worldwide.
© BWPDA May 03