A Technical Guide for Wine Producers

RECENT ARTICLES   |   WYNBOER HOME ABOUT POLES - AN OVERVIEW For further information, contact Andri Eloff, 082 8298971 or 023 3472413 (fax) 1. Introduction The following is a short discussion of wood treatment in South Africa. The treatment of timber is and has always been a science protected by the Forest Act. Current trends and changes make it necessary for the end user not only to understand what wood treatment is all about, but also what the future holds for the treatment of wood. Timber poles are still the most effective and cost saving necessity, but pitfalls can force farmers to investigate other alternatives. The nature and characteristics of a tree as natural raw material are discussed. Only by understanding where wood comes from may one better comprehend the science surrounding its treatment and preservation. 2. The living tree A tree consists of various parts, namely roots, trunk and bark, branches and leaves. Wood is produced in the trunk of a tree. By water absorption through the roots and photosynthesis through the leaves, nutrients are made available to the tree so that it may grow. Growth occurs not only in height, but also in circumference. The cambium is a thin layer of cells just below the bark which is responsible for this growth. The cross-section of a trunk clearly shows the most important elements responsible for the formation of wood. Figure 1 - Cross-section of a tree trunk The trunk may furthermore be divided into two sections, namely sapwood and heartwood. The heartwood is the middle section which also contains the pith and is surrounded by sapwood. It is formed when the function of sapwood cells changes from transporting and storing to reinforcing and preserving. In most species the heartwood is easily visible due to differences in colour between the sapwood and heartwood. Heartwood is usually slightly darker in colour. As the tree grows and increases in diameter, the heartwood girdle increases. Sapwood is responsible for transporting and storing water and nutrients. Why treated poles? 3. Durability of wood Durability of a species or a tree may be defined as the natural resistance to biological degradation (insects, fungi, etc). Different kinds of wood vary greatly in durability due to structure and chemical components. Both the macroscopic and microscopic nature determine the natural durability as well as the permeability of preservatives. When judging the suitability of wood for preservation, there are two very important factors which have to be investigated: durability (natural) permeability 3.1. Durability Regardless of the kind of wood, sapwood is never as durable as heartwood. The sapwood section has low natural durability. This is due to high moisture content, lower density than heartwood, as well as the presence of starch. These factors create favourable conditions for attacks by insects and fungi. The heartwood contains cells filled with chemical deposits, no starch and lower moisture content. In some species heartwood durability can be much higher than in others. 3.2. Permeability Permeability indicates how easily a specific species may be treated. In other words, the ease with which the preservative penetrates the wood and removes moisture. This characteristic is not only species dependent, but the composition of the tree itself is such that there are zones within the tree which may be more easily treated than others (sapwood and heartwood). In general the pine species are more permeable than the gum species and sapwood is more permeable than heartwood. 4. Treatment of wood 4.1. Degradation of wood Untreated wood is permanently exposed to biological degradation. Wood components are attacked by fungi and insects. The sapwood section in particular is rich in nutrients required for the survival of these organisms. A fungal attack will occur if conditions are favourable, in other words when there is sufficient food and oxygen and when temperature and moisture are optimal. Various kinds of fungi can harm wood in different ways, e.g. Brown rot, White rot and Soft rot. Wood borers or beetles can cause different degrees of damage. There is a wide variety of wood beetles, but all are subject to the four basic developmental stages, viz. eggs, larvae, cocoon and adult beetle. In most species damage is caused mostly by the larvae, which eat tunnels to find food. Examples of beetles attacking dry wood are wood borers, powder-post beetles, furniture beetles and long horn beetles. 4.2. Preservation/treatment of wood Hazard class Exposure class Preservative Retention, kg/m3 Penetration, mm Pine Gum H6 Marine CCA plus Creosote 24 plus 200 50 50 H5 Fresh water CCA or Creosote 16 or 130 25 20 H4 Outside, in contact with the soil CCA or Creosote 12 or 100 20 13 H3 Outside, above the soil CCA or Creosote 12 or 100 20 13 H2 Inside CCA or Creosote or TBTOL or PCPZN or Borate 12 or 100 or 1 or 6 or 5 20 13 4.2.1. Preservatives The durability of wood/poles is effectively improved by treatment with preservatives such as creosote, CCA (Copper Chrome Arsenate compounds), boron, etc. The most important factors influencing the effectiveness of the preservatives are: The extent of biological danger to which wood will be exposed (e.g. hazard class H4). The toxicity of the preservative used to fight the biological danger. Permanence of the preservative in the wood after treatment. Penetration and retention of the preservative. 4.2.2. Treatment processes To ensure that wood is sufficiently protected against biological dangers, it is important not only to use an effective preservative, but also to use the right process and procedure to treat the wood effectively. Process development goes hand in hand with research to develop the best preservatives against degradation. Two kinds of methods are used, and within each of these there are various procedures which may be followed to ensure penetration and retention of preservatives. Open tank process Pressure (cylinder) processes Click to see the maximum allowable defects in poles, guard rail posts, laths and round droppers Why SABS poles? 5. Standards 5.1. SABS and SAWPA SABS - South African Bureau of Standards SAWPA - South African Wood Preservers Association These two bodies are responsible for the development of standards in the preservation industry of South Africa. All preservers who are serious about their future and play a positive role in the preservation industry are members of SAWPA. Standards are drawn up, adjusted and revised in conjunction with the SABS in order to remain at the forefront of new technology and world trends. 5.2. Treatment standards The standards or specifications applicable to the wine industry are: SABS 457 - 1,2,3 - Wooden poles, droppers, laths, guard rail posts and spacing blocks Part 1 - General requirements Part 2 - Softwood species Part 3 - Hardwood species SABS 05 - Preservation of wood SABS 0255 - Safety in the wood preservation industry SABS 05 is a code of practice describing methods of treatment which may be used to preserve poles. SABS 0255 determines safety and environmental guidelines for the preservation industry. 5.3. Requirements which vineyard poles have to comply with In SABS 457 the requirements which vineyard poles have to comply with, can be divided into three groups, viz. Strength requirements Cosmetic requirements Treatment requirements Strength requirements are concerned with natural defects which may influence the strength of a pole. This includes defects such as knots, splits, checks, resin pockets, etc. Figure 3 - Requirements for knots and checks Cosmetic requirements include all those variations which affect the appearance of a pole rather than the strength or durability, e.g.crook, spiral grain, finish, dimensions, etc. Treatment requirements describe all the necessary requirements to ensure that each pole, in a certain hazard class, receives the right amount of preservative (retention) and is preserved to the required depth (penetration). Furthermore, that each pole is marked with the SABS stamp. 6. Conclusion Treatment of timber is a world-wide science requiring expertise to obtain the right results. Research determines which preservatives offer effective protection against biological attacks. Timber is an extremely important element of construction and measures have to be taken to ensure that it remains durable under all conditions and over a long period of time. SABS standards and the Forest Act are responsible, inter alia, for the protection of wood preservation and the end user against malpractice and wood which may not have been treated according to the current standards. Currently the treatment of vineyard poles is enforced and protected by the Forest Act, and the Act determines that all vineyard poles must comply with SABS 457. Furthermore, that the treatment processes to be used must comply with SABS 05. This means in effect that no treated pole may be sold without displaying the SABS stamp. Poles (pine and gum) therefore comply with specifications that have been scientifically developed to provide an end product which is not only acceptable to the end user, but also complies with the expected lifespan. Amidst these efforts to establish and maintain standards, however, there are cases of farmers being misled to purchase poles which do not comply with SABS standards. 7. Publications 1. SABS 457:1994 - Wooden poles, droppers, laths, guard rail posts and spacing blocks. 2. SAWPA. Understanding wood preservation - A guide to timber and its treatment against biological degradation. 3. SALMA. Introducing wood.

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