Making the most of local timber

Transcription

1 The Robinwood LadyMarian report: Making the most of local timber Durability, treatability and adding value

2 This report has been produced as a result of the Robinwood Project, a 45 month European Interreg 111c Regional Framework Operation project a first for Wales and delivered by Forestry Commission Wales on behalf of the Welsh Assembly Government. It looked at how we should manage our trees and forests to provide solutions to hydrological issues, increase the amount of wood used in heat and energy and the key role they play in helping to regenerate rural communities across Europe. The Italian project leaders named the project after Robin Hood a deliberate play on the UK folk hero best known for taking from the rich and giving to the poor. Research carried out by the project now provides valuable new information on how forests can provide all kinds of opportunities for the future.

3 3 RobinWood (LadyMarian) final report: Wales Contents 1 Introduction 4 2 Description of the project 5 3 Durability of Welsh timbers Natural durability Wood Preservation Wood Modification 7 4 Welsh timber resource 8 5 Raw material requirements Timber supply Timber selection and preparation Genetic considerations Sawing and drying Storage Compression wood Dead knots Growth rate 15 6 Permeability of Welsh timber 16 7 Experimental study into movement of Welsh timber Timber species collected Methodology Results 19 8 Wood modification What is wood modification Chemical modification Acetylation Furfurylation Thermal modification Impregnation / polymerisation processes The Indurite process The Belmadur process Other impregnation systems Enzymatic modification Conclusions on wood modification 27 9 Conclusion and recommendations 29 References 30 Appendix 1 Presentation given at LadyMarian closing meeting, Italy, September 2007

4 4 RobinWood (LadyMarian) final report: Wales Introduction Within the RobinWood project, Bangor University and BRE will undertake a thorough evaluation of the durability and treatability of timber species sourced from Welsh plantations, based on existing knowledge. The work described herein is split into two key tasks and will provide a baseline from which further studies may be undertaken, mainly through identification of knowledge gaps. The aim will be to demonstrate material of known properties that may enter the commercial market for specified end uses, such that a minimum product Service life should be guaranteed, provided correct maintenance schedules are followed. The evaluation will provide a compilation of known durability and treatment data, along with data from new tests for liquid uptake. This will provide a compendium of treatment properties that may be used within the Welsh timber sector.

5 5 RobinWood (LadyMarian) final report: Wales 1 Description of the project Local timber in many of the regions within the RobinWood Project region represent an under-utilised resource. Much of the local demand is met through imported timber, especially within the construction sector. Exploiting the natural timber resource would provide considerable benefit to local economies, increasing the commercial viability of local forestry. Among the important facts that need to be considered is the suitability of the local resource. There are a range of critical elements, each contributing to the overall selection, including strength, movement, durability and appearance. The work in this project will provide a baseline from which further studies may be undertaken for Welsh resources, mainly through identification of knowledge gaps, as well as providing a platform for assessment of properties of timbers from other nations in the RobinWood project. Historically, there was a demand for local timber for local construction. As markets have progressed from local to international supply and demand, many of the timber species previously used in local construction have been superseded with imported materials. Often the local resource is still capable of providing material of sufficient quality within the construction sector, but is competitively priced out of the market. The use of such material does gain credence when considering whole life and sustainability issues, where reduced transport costs represent a key benefit. The ability to use a local resource is also gaining acceptance in many areas, especially in niche market developments. Today, there is increasing demand for affordable housing, where timber is favoured. The use of local resources would provide considerable financial benefit to regional forestry sectors, though there would need to be a method to proove fitness for purpose. Timber used in construction has to meet a range of criteria, including durability, treatability, appearance and strength, depending on the given use of the timber element. The local timber resource provides a wide range of species that may be considered within construction, but with wide ranging properties. The objective of this project is to critically assess the durability and treatability of selected timber species, in order to determine their suitability within a local construction sector when applied to affordable housing. Through such actions, it will be possible to create a demonstrable market opportunity for locally sourced timber, providing much needed financial return from local forestry. A main aim of this work is to better demonstrate material of known properties that may enter the commercial market for specified end-uses. The evaluation undertaken within this sub-project will provide a compilation of known durability with determined treatment data, based on the uptake of liquid by selected timber species. This will provide a compendium of treatment properties for locally sourced timber, which in this case, could be used for the Welsh timber sector. The results achieved could also be issued as a benchmark for these timber species, should they be abundant in other RobinWood regions. Similar comparisons of timber from other regions would demonstrate any regional variations.

6 6 RobinWood (LadyMarian) final report: Wales 2 Durability of Welsh timbers All timber species have a degree of durability. These have been categorised in the past and these values (in some cases over 40 years old) are still used in evaluating timber today. Whilst these represent general values for specific species, they do not take into account the current supply of timber from plantation stock, nor the effect of regional variation. These may play a significant part in deciding whether a particular species is fit for a given application. There are ways in which the durability of a timber species may be enhanced, such as wood preservation and modification. Traditional methods of treating timber are being re-defined due to environmental implications. This has led to a restriction in the use of mainstream preservatives such as Copper- Chromium-Arsenic based preservatives (CCA), with it use banned in housing construction. This has led to the introduction of many new treatments. Some of these are direct replacements within the preservation industry, whilst others are new forms of treatment linked to modification processes. The ultimate aim of all these methods is to increase the durability of the timber, making it fit for use within construction by increasing its service life. Both Bangor University and BRE have considerable experience within these fields. 2.1 Natural durability Whilst there is some knowledge on the general durability of Welsh timber, these do not account for regional variation, variations in genetic stock etc. A thorough evaluation of available information will demonstrate suitability of selected timbers, as well as identifying where experiments will be required to assess actual durability ratings. The correct selection of material could allow increased service life of various structural components. BRE manages the UK national database of wood durability, though we note that data for Welsh timber is very limited. This piece of work would not only allow a thorough evaluation of existing information, but identify knowledge gaps where future laboratory and field testing would benefit the Welsh timber industry. The compilation of this information would not only allow correct selection of untreated material for various uses in timber construction, but would provide a knowledge base for future work. 2.2 Wood Preservation The concern with CCA is mainly due to the presence of arsenic. Currently many of the alternative wood preservatives depend upon copper, boron compounds and/or organic biocides. A range of different treatment recommendations exist for different timber species in different classes of use. These can also vary in terms of the required service life of the timber. BRE can develop treatment schedules for selected timber species. Future work could demonstrate the level of preservation afforded from these recommended treatment schedules through laboratory testing. BRE also has access to a 70 year database of the durability performance of wood preservatives.

7 7 RobinWood (LadyMarian) final report: Wales 2.3 Wood Modification An alternative method to conventional wood preservation is to change the characteristics of the wood. A range of techniques has been developed for doing this and they are classed as modification techniques, many of which are seen as environmental improvements on the use of conventional biocides. They also have the advantage of imparting excellent dimensional stability. Recently, the European Thematic Network for Wood Modification, of which BRE is co-ordinator and Bangor University was a key partner and work package leader, put forward a range of definitions outlining wood modification: A wood modification or technique is defined as the application of a substance or process to wood which results in a permanent change in the properties of the substrate. Permanent is defined as the design lifetime of a component made from the modified wood. Excluded from this definition is the application of a coating by painting, spraying or powder technique. The application of a biocide by painting, spraying or pressure/vacuum treatment was also similarly excluded. Once a series of Welsh timber species has been selected, the existing durability information for these may be reviewed, identifying any key gaps in the knowledge base. At this time, a decision as to the need to further test their durabilities will be taken.

8 8 RobinWood (LadyMarian) final report: Wales 3 Welsh timber resource The forestry sector has a long-standing position within the employment sector of the UK, though the majority of this is recognised through the larger Scottish forest coverage and associated companies. The Welsh timber sector, though not as advanced as that in Scotland, still represents a major financial and employment resource. When compared to other European countries, the forestry coverage within the UK appears to be fairly low, at 11.8% of the total land area (Forestry Commission 2002). The European context is shown in Figure 1 (Forestry Commission 2002). Figure 1: Overview of forest coverage within Europe (Forestry Commission 2002)

9 9 RobinWood (LadyMarian) final report: Wales Within Wales, there are approximately 288,000 hectares of forested land, split between Forestry Commission (FC) owned sites (39.2% of total forested area) and non-fc land (60.8%). Table 1 provides an approximate breakdown of the major species grown in Wales (Forestry Commission 2002). Softwood species Area (10 3 ha) Hardwood species Area (10 3 ha) Scots pine 5 Oak 43 Corsican pine 3 Beech 9 Lodgepole pine 6 Sycamore 7 Sitka spruce 84 Ash 19 Norway spruce 11 Birch 13 European larch 1 Poplar 1 Japanese / hybrid larch 22 Sweet chestnut 1 Douglas fir 11 Elm 0 Other conifer 6 Other broadleaves 18 Mixed conifer 0 Mixed broadleaves 8 Total softwood coverage 149 Total hardwood coverage 118 Table 1: Land coverage of major timber species in Wales (Forestry Commission 2002) Part of the remit of the Forestry Commission has been to ensure forest replanting and regeneration as part of the long-term commitment to providing a sustainable resource. To this end, Table 2 shows the planting dates for softwoods and hardwoods (Forestry Commission 2002). Softwood species Area (10 3 ha) Hardwood species Area (10 3 ha) Pre Pre present present 3 Total 149 Total 118 Table 2: Estimate of planting dates of Welsh timber resource (Forestry Commission 2002)

10 10 RobinWood (LadyMarian) final report: Wales Providing actual harvesting dates for the Welsh timber species is extremely difficult given factors involved, which include: Timber species Soil conditions Climate conditions (rainfall, sunshine, exposure to high winds) Required end-uses (i.e. level of maturity required for timber) For timber species with short rotational cycles (such as Sitka spruce) harvesting times within years may be possible. However where maturity is required (for example with oak), harvesting times of years may be possible. It is well documented that certain properties of timber may also improve as maturity increases. This is particularly so with natural durability. Thus, durability predictions for fast rotation grown timber may prove to be different from those conventionally quoted. However the older the timber, the greater the risk of heartwood decay, so reducing the value of the felled timber.

11 11 RobinWood (LadyMarian) final report: Wales 4 Raw material requirements The following sections cover some of the aspects that need to be considered when contemplating the processing and subsequent use of Welsh timber. 4.1 Timber supply In order to ensure a successful process, it is necessary to have a ready supply of material. Thus it would be recommended to base a process around a commonly grown timber species. Many studies have been carried out at university level using obscure timber species, often realising excellent results. However, there are no commercial prospects involved. Assuming a regular supply of material, it is prudent to base any treatment at a site close to the raw material. Modern methods of evaluation (such as Whole Life Costing) take into account transportation costs. Thus the transportation of material considerable distances will seriously affect the profitability of a given process. The need for timber processing equipment nearby to the treatment plant may also be a factor for consideration. Many treatments are more suited to treating processed boards rather than whole rounds. Smaller dimensions would also have faster treatment times, so reducing cost. There would be a balance between the volume capable of being treated at a given time and the actual treatment time. 4.2 Timber selection and preparation The raw material represents the limiting factor on any product. The properties of the material control the way products behave in service. It is necessary to ensure a high standard of starting material to ensure that quality products may be obtained. The main issues concerning timber quality are: Genetic considerations Drying and sawing material containing pith falling boards (thin boards sawn from the outside of the logs) Storage Compression wood Dead knots Growth rate

12 12 RobinWood (LadyMarian) final report: Wales Genetic considerations The use of genetically superior varieties of timber species is becoming more common, so that the speed of growth, reduction in branches and hence knots, straightness of trunk etc. can be fairly well controlled. In addition, modern forest management policies can provide a better quality timber Sawing and drying In order to achieve a good quality product, its conversion from the green state to timber ready for product manufacture is essential. Deformation of sawn timber during and after the drying process is the most important reason for down grading UK grown timber. Consultation with sawmills has indicated that between 10% and 12% of each kiln load is rejected due to excessive distortion occurring during drying. The deformation that occurs is related to the characteristics of the wood raw material (e.g. grain angle, density, juvenile wood content, compression wood and knots) and to kiln schedules, drying technology and the post-kiln conditioning treatments. New drying techniques (e.g. faster drying processes, top-loading) might assist in overcoming these problems. Pack design is a fundamental part of the kiln drying process. Correct stacking of packs will enhance the overall drying process and help to produce a high quality product, dried to a uniform moisture content, with very little or no distortion. This will make the product visually more acceptable to the buyer. Much of the distortion is found in pieces cut from close to the pith. It is envisaged that cladding is more likely to be produced from falling boards (thin boards sawn from the outside of logs). Falling boards are sawn far away from the pith and have less propensity to distort. However, they will also contain sapwood which is less durable. Analysis of data indicates significant variation of moisture content and distortion between mixed batches of wide (200 mm) and narrow (100 mm) pieces. Generally, wider pieces dry to a higher final moisture content than narrow pieces contained within the same load. It is therefore recommended that a kiln load be made up of parcels containing pieces with all the same dimension. If this is not possible then, wider pieces should be monitored for the desired moisture content, even if this means over-drying narrower pieces. Packs of timber containing pieces of different lengths may cause problems relating to stacking. Such packs are difficult to stack correctly and individual pieces are often un-supported at various points along their length, which increases distortion. If it is not possible to make up packs containing pieces of the same length, extra stickers should be incorporated to ensure each layer of pieces is adequately supported. To minimise distortion during the drying process, the stickers must be positioned at regular intervals across each layer of pieces, thus providing support to each successive layer. Pieces within a pack are therefore supported by those stickers above and below each layer as shown in Figure 2. In turn each pack should be supported by dunnage positioned below each column of stickers, supported by the kiln floor or bogie.

13 13 RobinWood (LadyMarian) final report: Wales Figure 2: Good stacking system for kiln drying Storage Once timber has been sawn and dried, storage may be necessary prior to its modification or its transportation to processors or end users. During this stage it is important that no re-wetting occurs. Whilst this is of reduced effect for modified timber, there is still a risk of the onset of biological degradation over long periods of time. In addition, re-wetting may increase the risk of warping coupled with irregular loading, which may in turn lead to material rejection. It is recommended that timber should be stored in a dry, well ventilated area, carefully stacked in packs, similar to those in correct kiln drying procedures. These have an even weight distribution, so reducing the risk of warp or creep during storage Compression wood Compression wood is a type of reaction wood which is produced by the tree in response to changes in its environment (e.g. constant wind damage). It is more common in fast-growing trees, where susceptibility to environmental changes is more pronounced and when exposed to prevaling winds. If a tree comes under an external force affecting its natural equilibrium position, compression wood is produced. This takes the form of promoted growth. The result is an eliptical growth pattern (Figure 3). Compression wood may form in any timber species and in any location. However, when exposed to prevailing coastal winds there is a greater tendency for compression wood to form.

14 14 RobinWood (LadyMarian) final report: Wales Figure 3: Formation of compression wood Compression wood results in instability in the longitudinal direction, such that warping and splitting may occur. When green compression wood dries, shrinkage of 5-8% is often commonplace, which is much higher than for normal wood. Thus the combination of both compression wood and normal wood will result in boards warping. The term warp refers to any deviation of the wood from its original plane, i.e. crook, bow, twist, spring and cup (Figure 4). The problems due to compression wood may be reduced by timber selection, sawing practices and by improved drying conditions. Figure 4: Bow and spring in wood Dead knots Knots are common features of timber. Dead knots are formed when an expanding trunk envelopes branch stem regions that have previously died, i.e. the trunk grows around a dead site. Dead knots often fall out during processing as they do not form a continuous part of the wood. They may also provide a focus for biodegradative attack.

15 15 RobinWood (LadyMarian) final report: Wales The presence and size of knots (especially dead knots) will play an essential part within timber selection. Some UK grown species such as Sitka spruce commonly have a lot of small knots. The presence of these smaller knots may not prove too problematic during wood modification processes. There is a greater risk of sound knots becoming loosened as a result of thermal treatment compared to chemical modification processes. Larger knots may need to be removed, as they will have a greater tendency to split or become loose. The production of clear engineered boards by jointing several smaller pieces of clear (defect free) material will provide a final product with better properties Growth rate The growth rate may be measured by the width of the growth ring. Usually the width of the growth rings increases as the cambium gets older and, after reaching a maximum width, it starts to decrease until the tree becomes very old. Changes may be possible from this typical scenario through silvicultural practices. In order to achieve a more accurate indication of changes to growth rate an index may be used, determined from the cambium age and apical age. Within a tree species, the basic wood density varies between genotype, stands and individual trees. Most of that variation is due to variation in wood basic density within individual trees between earlywood and latewood, from pith to bark, from ground level upwards and due to growth rate. The wood basic density usually increases with the age of the tree, often linearly. However, there is also a decrease of wood basic density with increased growth rate. In general, the fast growing species and, more specifically, younger specimens may not be suitable for use where strength is important (strength is reduced with faster grown and less dense timber). However for cladding, where the timber is only present as a non-load bearing product, this would not pose such a problem.

16 16 RobinWood (LadyMarian) final report: Wales 5 Permeability of Welsh timber Wood is an extremely complex material in its moisture characteristics. In the growing tree, the organisation and function of the different cells is designed to ensure efficient transport of water and mineral solutions upward from the roots to the leaves. Because of its anatomy, timber is highly anisotropic in its moisture transmission characteristics. The rate of movement of moisture axially, i.e. along the grain direction, is many times higher than the rate of movement in the lateral directions (Table 3). There are also smaller differences in moisture transmission rates in the principal lateral directions, again for anatomical reasons. The rate of moisture movement in the radial direction is usually rather higher than that in the tangential direction, because of the presence of the radially aligned ray cells. Species Pine sapwood Pinus sylvestris Pine heartwood Pinus sylvestris Norway spruce Picea abies Western red cedar Thuja plicata Douglas fir Pseudotsuga menziesii Beech Fagus sylvatica Lime Tilia vulgaris Uptake g/m 2 in 30 mins Axial penetration Lateral penetration Table 3: Typical uptake of liquid water for different wood species, obtained using Initial Surface Absorption Test (ISAT) measurements Moisture absorption rates vary considerably between different species. Again, there are often obvious anatomical reasons why a particular species shows high moisture absorption or moisture resistance. Spruce, for example, is relatively resistant to moisture penetration because the pits the connecting pathways between adjacent cells become blocked during kilning or drying. The details of the drying process can thus greatly affect the permeability of the dried timber. Within a given species, the heartwood

17 17 RobinWood (LadyMarian) final report: Wales tends to be less permeable than the sapwood, partly because the pits can also become blocked as the heartwood is formed. In the heartwood especially, further restriction of moisture movement can result from the deposition of waste materials around the pits. In hardwood species, axial flow is often very high because of the presence of long open cells known as vessels, which can behave like capillaries. The following represent literature estimates for the permeability of the major timber species grown in Wales. Given the heterogeneous nature of timber, these values can vary considerably from tree to tree and in cases within a single tree (depending on the nature of timber being tested, i.e. the presence of compression wood). The permeability values quoted refer to those noted for preservative treatment, though similar values should be noted for other liquid treatments of similar viscosity. In terms of permeability ratings, there are four recognised classifications: Permeable this classification is for timbers that may be completely penetrated under pressure without any difficulty. This means they may be heavily impregnated using an open tank process. Moderately resistant these species are relatively easy to treat, often to lateral penetrations of up to 1.9 cm after a period of 2-3 hours under pressure. Resistant this classification is for species difficult to impregnate under pressure, thus requiring long treatment periods. Lateral penetration is usually to a maximum of 0.6 cm. Extremely resistant - this final classification is for species that are virtually incapable of taking up treatment, even after long pressure schedules. There is virtually no lateral penetration. Table 4 gives an overview of the expected permeabilities of the heartwood of major Welsh timber species, with most sapwoods being rated as permeable. Softwood species (Henderson 1956) Permeability Hardwood species (Farmer 1972) Permeability Scots pine Moderately resistant Oak Extremely resistant Corsican pine Moderately resistant Beech Permeable Lodgepole pine Resistant Sycamore Permeable Sitka spruce Resistant Ash Moderately resistant Norway spruce Resistant Birch Permeable European larch Resistant Poplar (hybrid) Not available Japanese / hybrid larch Resistant Sweet chestnut Extremely resistant Douglas fir Resistant Elm Moderately resistant Table 4: Overview of permeability of heartwood of major Welsh timber species

18 18 RobinWood (LadyMarian) final report: Wales 6 Experimental study into movement of Welsh timber In order to assess permeability of currently available Welsh timber, a study was undertaken whereby a range of sourced species were tested according a series of soak dry analyses. 6.1 Timber species collected Table 5 provides a list of the species considered during this study, showing that the majority of the timber originated from South Wales. Species Latin name Origin of sample Oak Quercus robur Usk, Monmouthshire Spelted Beech Fagus sylvatica Usk, Monmouthshire Heat treated Beech Fagus sylvatica Tregynon, Powys Beech Fagus sylvatica Usk, Monmouthshire European Larch Larix decidua Tregynon, Powys European Lime Tilia vulgaris Cardiff European Ash Fraxinus excelsior Monmouth, Monmouthshire Sweet Chestnut Castanea sativa Monmouth, Monmouthsire Sycamore Acer pseudoplatanus Merthyr, Rhonda Cynon Taff Elm Ulmus procera Nelson, Rhondda Cynon Taff Walnut Juglans regia Monmouth, Monmouthshire Holly Ilex aquifolium Cardiff Yew Taxus baccata Monmouth, Monmouthsire Alder Alnus glutinosa Newport, Gwent Douglas fir Pseutotsuga menzieii Tregynon, Powys Hybrid poplar Populus spp Tregynon, Powys London plane Platanus hybrida Cardiff Western red cedar Thuja plicata Cardiff Cherry Prunus avium Cardiff Red oak Quercus rubra Monmouth, Monmouthshire Cedar Cedrus spp Cardiff Sitka spruce Picea sitchensis Wentwood, Gwent Table 5: Overview of Welsh timber species tested 6.2 Methodology The following test methodology was employed during this study: The following work needs to be carried out. 1. Code all samples using the lettering code in the table above, with a number identifier. For example for spruce S1, S2, S3 etc.

19 19 RobinWood (LadyMarian) final report: Wales 2. Weigh and measure all samples under laboratory conditions. Measurements to be done on all three directional faces of the timbers (length, breadth, depth usually this would be longitudinal, radial and tangential, some samples may not be cut in correct fashion). Record information. 3. Place samples in an oven at 103 o C for a period of 16 hours (overnight) 4. Remove from oven, allow to cool in a dry atmosphere (e.g. in desiccators). 5. Weigh and measure (as described in (2) above). Record all information. Calculate moisture contents from ambient conditions, and dimensional changes. 6. Place in conditioning room (65% relative humidity, 20 o C), for a period of 3 weeks, weighing and measuring samples twice per week. Record all information from each series of measurements (conditioning 1, conditioning 2, conditioning 3 etc.) 7. After 3 weeks place in oven at 103 o C for a period of 16 hours (overnight). 8. Remove from oven, allow to cool in a dry atmosphere (e.g. in desiccators). 9. Weigh and measure (as described in (2) above). Record all information. Calculate moisture contents from ambient conditions, and dimensional changes. 6.3 Results Table 6 provides an overview of dimensional and weight changes noted as a result of experiments carried out. It is important to consider that not all samples were prepared with directions perpendicular to surfaces. This resulted in angular grain structure across some of the samples, which would have a considerable effect on the radial and tangential dimensional movement noticed. Results obtained seem to show greater degrees of movement for several of the softwood species compared to literature evidence (Henderson 1956), whilst hardwood samples resulted in samples closer to literature values compared to the softwoods. This may be further explained through: (i) (ii) (iii) quality of timber used many of the timber species tested were individual trees felled as a result of silvicultural practices by local councils number of replicates tested a full dimensional movement test would require approximate 20 replicates per species. Typically a maximum of 5 samples were tested, owing to material restriction. Heartwood / sapwood mixture in samples being tested. The literature samples (Henderson 1956) refer to heartwood samples, whereas material tested may have varying proportions of heartwood and sapwood (again due to material restrictions).

20 20 RobinWood (LadyMarian) final report: Wales Species Weight change (%) Dimensional change (%) Longitudinal Radial Tangential Oak Spelted Beech Heat treated Beech Beech European Larch European Lime European Ash Sweet Chestnut Sycamore Elm Walnut Holly Yew Alder Douglas fir Hybrid poplar London plane Western red cedar Cherry Red oak Cedar Sitka spruce Table 6: Results of dimensional movement experiments Given the level of dimensional movement noted for the samples tested, it would be wise to consider methods capable of increasing the stability of the wood substrate. An emerging technology dealing with this is wood modification, and will be dealt with specifically in the next chapter.

21 21 RobinWood (LadyMarian) final report: Wales 7 Wood modification Wood modification has progressed from the original laboratory based experiments of the 1920's and 1930's to being commercially viable processes today. Much of this has been due to a greater understanding of the science and engineering required for the processes. There are a range of possible wood modification methods, chemical, thermal, impregnation / polymerisation and enzymatic, with most of the technological advances having been in the first three modification types to date. This paper will provide an overview of the methods and processes involved, as well as demonstrating where work has been carried out to date on the bonding capacity of such treated materials. Timber, by its very nature, is degradable, with the rate of degradation dependent on the species and its use. The majority of European timber species (especially softwoods) are classed as slightly durable or nondurable, making their use, especially in-ground contact uses (Use or Hazard Class 4), limited. This could often be achieved in the past through preservation techniques. However, increased environmental awareness by the general public, combined with increasingly stringent legislature in recent years has led to greater restrictions in the use and disposal of many of the conventional preservative systems. This has led to three possibilities: Moving away from the use of timber in certain cases The development of new wood preservation systems The creation of new protection methods The first of these has been a key marketing strategy of non-wood materials, focussing on the perceived failings of timber, especially given the restriction of use of selected wood preservation systems (such as Chromated Copper Arsenate (CCA)). However the timber industry has begun fighting back through activities in the second and third points listed above. Indeed, the development of new protection methods has led to a whole new area of research, development and commercialisation, namely wood modification. Wood modification has been well documented in recent years (Hill 2006), and to attempt to cover all aspects of wood modification within this paper would not be possible. Instead, this paper will summarise some of the key modification processes, where commercialisation has occurred or is about to occur. Furthermore, emphasis will be placed on adhesive properties, where they have been reported to date. 7.1 What is wood modification Hill (2006) provided an all-encompassing definition for wood modification: Wood modification involves the action of a chemical, biological, or physical agent upon the material resulting in a permanent change to the polymeric chemical composition; with such a change leading to a desired property enhancement. The modified wood should itself be non-toxic under service conditions and furthermore, there should be no release of any toxic substances during service, or at end of life following disposal or recycling of the modified wood.

22 22 RobinWood (LadyMarian) final report: Wales Such a definition discerns wood modification from wood preservation, where substances recognised for their toxicity to invading organisms tend to be used. The acceptance of wood modification may be noted when the International Research Group on Wood Preservation changed its name to the International Research Group on Wood Protection in Whilst the commercialisation of wood modification is a fairly recent event, several wood modification processes have been in development for several decades. It is only through increased environmental concern, greater understanding of chemical and engineering processes and financial factors that wood modification has become commercially viable. The following sections deal with some of the more common wood modification processes. 7.2 Chemical modification Whilst the definition of wood modification is generic, the definition for chemical modification (Rowell et al 1988) is more specific: "Chemical modification is any chemical reaction between some reactive part of the wood cell wall component and a simple single chemical reagent, with or without catalysis, that forms a stable covalent bond." There are two major chemical modification processes commercially available; acetylation and furfurylation Acetylation The acetylation of wood with acetic anhydride has been studied intensively and shown to be one of the most promising methods for improvement of the technical properties of wood products. During the reaction of the wood with acetic anhydride hydroxyl groups of the cell wall polymers are converted into acetyl groups (Figure 5). wood + acetic anhydride ----> acetylated wood + acetic acid Figure 5: The acetylation process During the reaction, acetic acid is formed as a by-product that can be converted into acetic anhydride again. Like untreated timber, the modified wood consists only of carbon, hydrogen and oxygen and it contains no toxic elements.

23 23 RobinWood (LadyMarian) final report: Wales Research has shown that acetylation of solid wood can improve certain properties of this material considerably: The durability of the wood is improved to durability class 1 (better than teak wood) The wood will gain a reduction in swelling and shrinkage of 70-80% compared to untreated wood due to a lower uptake of water An increase of 30 % of the hardness of the material can be reached The treatment has no impact on strength properties of the material The treatment has no impact on the appearance of the material The UV-resistance of the wood is improved considerably Commercialisation has been achieved by TitanWood in The Netherlands (Figure 6), with the launch of Accoya for solid wood, whilst activities continue in Sweden (Figure 7) for the commercialisation of fibre acetylation. Figure 6: Acetylation in Netherlands Figure 7: Acetylation in Sweden Furfurylation Furfurylation is a process based on the reaction of wood with a bio-based chemical, furfuryl alcohol (FA) at the cell wall level. The result is a new material, that has been recognised as an environmentally friendly polymer. FA is a bio-based chemical processed from bagasse (sugar canes), corn cobs or other agricultural rest products. The WPT process is based on traditional impregnation equipment, followed by a curing step.

24 24 RobinWood (LadyMarian) final report: Wales The modified wood enhances the properties of wood in several areas: Protection against decay, as a result of reduced moisture and altered wood chemistry Increased dimensional stability, as a result of permanent swelling of the cell wall Increased hardness as a result of polymer in the cell lumens Golden brown appearance Decreased hygroscopicity The development of furfurylated wood has been led by WPT in Norway (Figure 8), who is currently promoting three technologies based on this technolgoy; VisorWood, Kebony and Kebony Dark. Figure 8: Furfurylation plant in Norway 7.3 Thermal modification In addition to the general review of thermal modification as a single area of wood modification (Hill 2006), there has also been a comprehensive review of thermal modification (Rapp 2001). Whilst non-durable softwoods have been the principal focus of heat treatments in Europe, there have also been examples of other species being treated, including albizzia (Sudiyani et al. 1999) and eucalyptus species (Santos 2000). The development of a heat treatment process at industrial scale using a mild pyrolysis process and other heat treatments have been developed in France where the process of heating dry wood to temperatures above 200 C in an inert atmosphere is called retification and the product is called retified wood (Vernois 2001). There are four plants manufacturing this product in France and more are expected to come on stream in the next few years. Heat treatments have also been developed in France where the process of heating wet wood to 230 C provides a saturated steam atmosphere for protection of the wood (Vernois 2001), similar to the process developed in Finland. The process developed in Finland in the 1990s uses water vapour derived from the timber moisture content as the shielding gas to prevent deleterious breakdown of the wood structure. The product is called ThermoWood. The timbers are typically pine, birch and sometimes spruce species that can be treated

25 25 RobinWood (LadyMarian) final report: Wales green or kiln dried. The three stages are the temperature rise, the treatment stage and the cooling phase which are all carefully controlled in relation to the core temperature of the timber. The process liberates small amounts of acetic acid and phenolics which requires acid resistant stainless steel vessels to be used for treatments (Jämsä and Viitaniemi 2001). Temperatures between 180 C and 250 C are used to alter the physical and chemical properties of wood permanently. The changes that occur on heating wood and producing the modified product can be monitored using Fourier transform infra red spectroscopy (FTIR). Kotilainen et al. (2000) provides an introduction to the handling of the FTIR data by principle component analysis. A summary of research on heat treatments in Finland is provided by Syrjanen (2001) and the effect of heat treatments on the properties of spruce has also been published. The properties of timber that are changed by heat treatments include: colour, which changes to dark or mid brown, but is not UV stable the equilibrium moisture content, which is reduced by 50% the shrinking and swelling, which are also reduced by 50-90% the biological durability out of ground contact, which is improved the mechanical properties, which are reduced by up to 30% (Jamsa & Viitaniemi 2001). Whilst ThermoWood represents the most commercially advanced thermal modification, there are a range of other treatments that are, or are about to become commercially. Among these are New Option Wood and Perdure (France), Lignius and Lambowood (Netherlands), Barkett (Germany / Russia), WTT (Denmark) and Huber Holz and ThermoHolz (Austria). Developments are continuing with other companies in these and other countries. In addition to conventional thermal modification treatments, high temperature treatment in the presence of steam may be regarded as hydrothermal treatment. Steaming or heating wood in a compressed state improves hardness but results in slight decreases in other mechanical properties. It also produces a slight darkening in colour and no recovery of set (Inoue et al., 1993). The compression of wood while heating (170 o C) causes lignin flow (in effect a rearrangement of the cementing material between the cellulose fibres) to relieve the internal stresses. This greatly reduces the tendency of wood to swell when wet and increases the strength. This product (Staypak) is used commercially for tool handles, mallet heads, jigs and dies in the United States (Rowell and Konkol, 1987). Heating wood under vacuum without compressing it still causes lignin flow and increases in stability, though the strength decreases. This product (Staybwood) is not commercially used (Rowell and Konkol, 1987). The Plato-process developed in the Netherlands for thermal modification of nondurable timber species involves a hydrothermal treatment followed by a drying and curing stage (Boonstra et al. 1998). This process produces a material with greater dimensional stability and improved durability aspects (Tjeerdsma et al. 1998). In the "Plato-process" the hydrothermal treatment is a two stage process, firstly the green wood is heated in aqueous solution to 200 C, where the pressure reaches 20 bar and selective depolymerisation occurs. In the second stage the aldehydes and phenols react once more with each other creating a polymer network (Hekhuis 1996). Characterisation of thermally modified wood including the cross linking and rearrangements at molecular levels that occur upon heating during the Plato-process are reported by Tjeerdsma et al. (1998) and Boonstra et al (2007). Heat treatments have also been conducted in combination with a conventional wood protection chemical and the report of biological resistance of steam compressed wood that had been pre-treated with boric acid. Though the added value through performance improvements of these composite treatments is not known.

26 26 RobinWood (LadyMarian) final report: Wales Using oil to transfer heat to the wood and protect it from damaged at high temperatures has been used in a number of simple treatments, an example is fence posts treated in hot tall-oil (complicated mixtures of natural pine oils extracted from forestry waste) baths in Finland. Promising results have been achieved using these tall oils but this work is hindered by the vast number of derivatives that could potentially be used and the quality control and performance of treated batches of material. On the other hand it is a very simple and accessible way of treating timber to generically enhance timber durability, perhaps with an application in more remote communities. A hot-oil treatment has been commercially developed and patented by Menz Holz in Germany using vegetable oils, such as rape seed oil, as the heat transfer agent (Rapp and Sailer 2001). Oil-heat treatment of Scots pine and spruce improved the dimensional stability and biological resistance of the product (Sailer et al. 2000). Natural plant oils lend themselves to the oil-heat improvement of wood from an environmental point of view and because of their physical and chemical properties, and as renewable raw materials they are CO 2 neutral. 7.4 Impregnation / polymerisation processes The use of impregnation / polymerisation processes is potentially a more simple wood modification system than chemical modification (e.g. acetylation) as the technology involved can be considered more closely associated to the impregnation processes employed by traditional wood preservation methods, followed by a high temperature process. The furfurylation process already described within chemical modification, may be considered an impregnation / polymerisation process. The major difference between an impregnation / polymerisation process and a chemical modification process is that the chemical bonding of the agent to the wood cell wall constituents does not occur, or has not yet been proven. In many cases, the agent can be considered a cell all bulking agent. There are two main impregnation / polymerisation processes at commercial level, namely the Indurite and Belmadur technologies The Indurite process The Indurite process developed from a comprehensive survey of possible reactions of wood cell wall analogues with polymer systems. As such, starch, cellulose, hemicelluloses and lignin-carbohydrate complexes were considered, along with maltodextrin. Laboratory evaluations led to the implementation of maltodextrin with melamine resins to yield a water-based treatment system. The original concept for Indurite was undertaken in New Zealand, in a successful attempt to upgrade home-grown radiata pine (Pinus radiata), in terms of surface hardness, performance in service and durability. The Indurite process has led to several spin-off treatment processes, using different wood component analogues. At the same time, the Indurite process is being commercialised by Osmose The Belmadur process The Belmadur process has been commercialised by BASF, with technology transferred from the treatment of non-wood systems. This development uses 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU), whose use is commonplace within the fabric and textile industries in the production of wrinkle-free fabrics. From some of the earliest examples of the use of DMDHEU in wood treatment (Militz 1993), the process

27 27 RobinWood (LadyMarian) final report: Wales has undergone considerable evaluations (for example Krause et al. 2003, Xie et al. 2005), from which commercial application has been achieved Other impregnation systems Other methods that have been evaluated at laboratory scale include the use of vinyl monomers (styrene, methylstyrene, methyl methacrylate, diallyl phthalate, acrylonitrile, acrylamide and N-methylolacrylamide) which result in a wood hardening (Beall and Witt 1972, Smith and Sutton 1971), and the use of phenolformaldehyde resins in a method based on the Impreg process (Stamm and Seborg 1955). 7.5 Enzymatic modification The use of enzymatic modification represents an emerging technology better suited to fibre treatment, given the size exclusion factors affecting enzymes entering the wood cell wall structure. The aim of enzymatically treating fibres is to create activated fibres capable of improved binding in composite manufacture. Much of the work carried out to date has considered glueless systems, where the activated sites in the fibres are capable of self-bonding, though the use of adhesives is also possible. The most common enzyme used is laccase. The process of enzyme catalysed bonding of fibreboards is based on the reaction of lignin with the enzyme at the fibre surface. These activated lignins can then act as an adhesive, i.e. they undergo fibre to fibre cross-linking. This is due to the laccase forming stable radicals, which are capable of reacting during the hot pressing stage in fibreboard manufacture. The enzymatic treatment of beech fibres has been carried out on a pilot plant scale. Results for self-bonded boards showed that comparable results to UF-glued boards could be achieved. There was also evidence of increased molecular weight of the lignin. ESR/EPR studies have proven the presence of long-lived phenoxy radicals in the lignin, indicating that it might be possible to treat fibre and store for considerable time before their use in board manufacturing. 7.6 Conclusions on wood modification Wood modification, after several decades of research and development, has finally reached commercial status, with several forms of modified wood now available. The choice of treatments will continue to increase as more treatments progress from laboratory scale to industrial scale production. Depending on the final use of the timber, a range of treatments are now possible. On a general conclusion, the availability of treatments is summarised in Table 8. A survey in Sweden predicted an interest by local companies in modified wood in the following areas (Table 7), along with the anticipated treatment of interest. The last line (referring to furniture manufacture), represents an assessment of current methods available.

28 28 RobinWood (LadyMarian) final report: Wales Product range Garden Wood Window Companies Exterior Door Companies Flooring Companies Wet Room & Façade Panels Building products etc. Automotive / Nautical industry Architects /Gov. organizations Furniture manufacture Possible treatment process Thermally modified wood Acetylated wood / Polymer impregnated Acetylated MDF Modified wood / MDF / Polymer impregnated Acetylated fibres Acetylated / Heat modified wood Furfurylated wood Acetylated /Heat modified wood Acetylated / Furfurylated / Polymer impregnated Table 7: overview of perceived modification techniques in various uses. Table 8 provides an evaluation of current and imminent availability of modified materials. Modification Likelihood of availability Solid wood Veneers Fibres Acetylation Yes Yes Yes Within 1-2 years < 5 yrs <10 yrs Furfurylation Yes Yes Possible Current <10 yrs DMDHEU Yes Yes Possible Within 1-2 years <5yrs Heat treatment Yes Yes Possible Current <5 yrs <10 yrs Table 8: Availability of modified wood

29 29 RobinWood (LadyMarian) final report: Wales 8 Conclusion and recommendations Whilst the total land coverage of forests in Wales in low compared to many European countries, the timber industries and those affiliated to them represent key employment and financial sectors. There are two main species grown in the region, Sitka spruce (softwood) and oak (hardwood), though there are also several other species that may represent commercial viabilities, depending on the scale of production aimed for. Many of these lower volume species represent excellent stock for small and medium sized enterprises (SME s) within the region and beyond. Literature evaluations of the permeability of the major Welsh timber species have been compiled, from which a test programme for a range of samples of Welsh hardwoods and softwoods was compiled. Results appear to vary from those reported within the literature, though there was no observed correlation (i.e. whether results were typically higher or lower than those quoted in the literature). Results would seem to suggest the need for a more systematic series of tests, where samples would be derived from several trees. Obtaining materials from a range of localities might also help identify a regional effect, should it exist. The use of Welsh timber is growing, though there is the need to ensure the correct material is used in a given use. It is important to assess the properties of a timber before using it, not only in terms of its mechanical performance, but also its durability and dimensional stability. Many Welsh (and European) timber species (and especially those of commercial importance) exhibit moderate to high dimensional movement and only moderate durability. Thus considering ways of improving the behaviour of the timber might prove advantageous. One method for doing this would be through the use of wood modification technologies.

30 30 RobinWood (LadyMarian) final report: Wales References Beall, F.C. and Witt, A.E. (1972). Polymerisation of methyl methacrylate by heat-catalyst and gamma irradiation methods. Wood and Fiber, 4(3), Boonstra, M.J., Tjeerdsma, B.F., and Groeneveld, H.A.C. (1998). Thermal modification of non-durable wood species. 1 The PLATO technology: thermal modification of wood. International Research Group on Wood Preservation-No IRG/Wp/ , 13. Farmer R.H. (1972). Handbook of Hardwoods. Building Research Establishment Princes Risborough Laboratory. HM Stationery Office. SBN Finnish ThermoWood Association (2003). ThermoWood Handbook. Forestry Commission (2002). Forestry Statistics A compendium of statistics about woodland, forestry and primary wood processing in the United Kingdom. ISBN Henderson F.Y. (1956). A handbook of softwoods. Forest Products Research Laboratory. HM Stationery Office. ISBN Hekhuis, H.J. (1996). Plato: populier als tropish hardhout. ; Plato: poplar as a tropical hardwood. Netherlands Bosbouwtijdschrift, 68(4), Hill, C.A.S. (2006). Wood Modification chemical, thermal and other processes. Wiley Series in Renewable Resources, 260pp. J. Wiley and Sons. ISBN-10: Inoue, M., Norimoto, M., Tanahashi, M. and Rowell R.M. (1993). Steam or heat fixation of compressed wood. Wood & Fiber Science, 25(3) Jämsä, S. and Vittaniemi, P. (2001). Heat treatment of wood Better durability without chemicals. In Review of Heat Treatments of Wood. Ed. A.O. Rapp (2001). ISBN Kotilainen, R.A., Toivanen, T.J. and Alen, R.J. (2000). FTIR monitoring of chemical changes in softwood during heating. Journal of Wood Chemistry and Technology, 20(3) Krause A., Jones D., van der Zee M. and Militz H. (2003). Interlace Treatment Wood Modification with N- Methylol Compounds. Proceedings of the First European Conference on Wood Modification ISBN Militz H. (1993). Treatment of timber with water soluble dimethylol resins to improve their dimensional stability and durability. Wood Science and Technology 27, Rapp, A.O. (2001). Review of Heat Treatments of Wood. ISBN Rapp, A.O. and Sailer, M. (2001). Oil heat treatment of wood in Germany State of the art. In Review of Heat Treatments of Wood. Ed. A.O. Rapp (2001). ISBN

31 31 RobinWood (LadyMarian) final report: Wales Rowell, R.M. and Konkol, P. (1987). Treatments that enhance physical properties of wood. United States Department of Agriculture, Forest Service, Forest Products Laboratory general technical report FPL-GTR- 55. Sailer, M., Rapp, A. O., Leithoff, H and Peek, R.-D. (2000). Vergütung von Holz durch Anwendung einer Öl- Hitzebehandlung. Holz als Roh- und Werkstoff, 58, Santos, J.A. (2000). Mechanical behaviour of Eucalyptus wood modified by heat. Wood and Science Technology, 34(1), Smith, R.M. and Sutton, H.C. (1971). Studies on wood-plastic materials made from New Zealand woods. 1, Pinus radiata methyl methacrylate. Report INS-R-90. DSIR, Wellington, NZ. Stamm, A.J. and Seborg, R.M. (1955). Impreg, Compreg. Forest Products Laboratory, USDA Forest Service, 1380, Sudiyani, Y., Takahashi, M., Imamura, Y. and Minato, K. (1999). Physical and biological properties of chemically modified wood before and after weathering. Wood Research, 86, 1-6. Syrjanen, T. (2001). Production and classification of heat treated wood in Finland. In Review of Heat Treatments of Wood. Ed. A.O. Rapp (2001). ISBN

32 32 RobinWood (LadyMarian) final report: Wales Appendix 1 Presentation given at LadyMarian closing meeting, Italy, September 2007 Options for Welsh timber Dr. Dennis Jones Woodknowledge Wales / BRE Wales Welsh timber Mainly Sitka spruce (picea sitchensis) Planted for use in coal industry Fast growing Knotty Hard to harvest (terrain, climate) Better material from other countries Scandinavia Baltic region Need to find better outlet Innovation Best use

33 33 RobinWood (LadyMarian) final report: Wales Timber availability Softwood species Area (10 3 ha) Hardwood species Area (10 3 ha) Scots pine 5 Oak 43 Corsican pine 3 Beech 9 Lodgepole pine 6 Sycamore 7 Sitka spruce 84 Ash 19 Norway spruce 11 Birch 13 European larch 1 Poplar 1 Japanese / hybrid larch 22 Sweet chestnut 1 Douglas fir 11 Elm 0 Other conifer 6 Other broadleaves 18 Mixed conifer 0 Mixed broadleaves 8 Total softwood coverage 149 Total hardwood coverage 118 Permeability of Welsh timber Softwood species (Henderson 1956) Permeability Hardwood species (Farmer 1972) Permeability Scots pine Moderately resistant Oak Extremely resistant Corsican pine Moderately resistant Beech Permeable Lodgepole pine Resistant Sycamore Permeable Sitka spruce Resistant Ash Moderately resistant Norway spruce Resistant Birch Permeable European larch Resistant Poplar (hybrid) Not available Japanese / hybrid larch Resistant Sweet chestnut Extremely resistant Douglas fir Resistant Elm Moderately resistant

34 34 RobinWood (LadyMarian) final report: Wales Evaluating movement of timber Look at variety of species in Wales Material from towns and countryside Assess how much samples shrink and swell under extreme conditions Oven dry to water soaked Will help determine possible uses of timber Small movement better for products in varying humidity conditions Species used in test English name Oak Latin name Quercus robur English name Holly Latin name Ilex aquifolium Spelted Beech Fagus sylvatica Yew Taxus baccata Heat treated Beech Fagus sylvatica Alder Alnus glutinosa Beech Fagus sylvatica Douglas fir Pseutotsuga menzieii European Larch Larix decidua Hybrid poplar Populus spp European Lime Tilia vulgaris London plane Platanus hybrida European Ash Fraxinus excelsior Western red cedar Thuja plicata Sweet Chestnut Castanea sativa Cherry Prunus avium Sycamore Acer pseudoplatanus Red oak Quercus rubra Elm Ulmus procera Cedar Cedrus spp Walnut Juglans regia Sitka spruce Picea sitchensis

35 35 RobinWood (LadyMarian) final report: Wales Results of movement tests (1) Species Weight change (%) Dimensional change (%) Longitudinal Radial Tangential Oak Spelted Beech Heat treated Beech Beech European Larch European Lime European Ash Sweet Chestnut Sycamore Elm Walnut Results of movement tests (2) Species Weight change (%) Dimensional change (%) Longitudinal Radial Tangential Holly Yew Alder Douglas fir Hybrid poplar London plane Western red cedar Cherry Red oak Cedar Sitka spruce

36 36 RobinWood (LadyMarian) final report: Wales Upgrading timber Improved treatments for wood Modifications Use of new preservatives Incising techniques Methods cannot work miracles Need basic grade of starting material, inferior wood cannot be made fantastic Manufacture of composites for the construction industry Wood modification: Why modify wood Improving the performance of wood by modifying its molecular structure Potential property improvements Durability Moisture resistance Dimensional stability Paint adhesion Colour End of life!! Create new markets for local timber Hope to compete against imported hardwoods Promote sustainable timber sources

37 37 RobinWood (LadyMarian) final report: Wales Acetylation Reaction with acetic anhydride Commercially available Titanwood (Accoya) Over 40 years laboratory results Furfurylation Treatment with furfuryl alcohol Recognised as environmentally friendly Commercially available (WPT)

38 38 RobinWood (LadyMarian) final report: Wales Thermal treatment Range of commercial operations Heat in absence of oxygen Severity of treatment affects looks and properties Impregnation / polymerisation Belmadur Based on DMDHEU Used in textiles industries Developed in Germany Commercialisation by BASF

39 39 RobinWood (LadyMarian) final report: Wales Impregnation / polymerisation Indurite Developed in New Zealand Starch-based treatment Bought out by Osmose Regarded as wood into wood Enzymatic treatments Mainly based on laccase Activate sites on lignin Auto-adhesion of fibres Suited to composite manufacture C C C Laccase. O O(Me) O OH. C C C O. O(Me)

40 40 RobinWood (LadyMarian) final report: Wales Timber Cladding Maintaining its position within mainland Europe Increasing in popularity in the UK One day conference September 2005 attended by 250 persons Current trend use timbers of higher natural durability Imported Western red cedar High quality larch Opportunities for modified wood Opportunities for new coating systems Benefits of coatings Increase service life Extend service life of lower DC species Reduce moisture uptake Provide a barrier to biological decay Aesthetics A product that keeps its looks 35 Effect of coating on Sitka spruce (north Scotland) Effects of coatings considered as part of BRE project on cladding Moisture content (%) Demidekk Uncoated

41 41 RobinWood (LadyMarian) final report: Wales Wood Modification Several possible systems may be used Heat treated Furfurylated Acetylated Untreated Mini-clad system Uncoated Long term material performance All affected by weathering Reduced m.c Increased stability Green gluing Recognised way of removing defects from timber More uniform product No limitation to number of joints or overall length Inside out beam