J.D. Brazier and C. Webster
J.D. BRAZIER and C. WEBSTER are with the United Kingdom's Princes Risborough Building Research Establishment.
For more efficient utilization of forest resources, especially in the tropics
Widespread use of tropical hardwood developed in most industrialized countries in the post-Second World War period and since that time has steadily increased. Thus, in the past decade, exports of tropical hardwood have multiplied threefold, with by far the greatest volume increase coming from the southeast Asian countries. Today, three territories, Malaysia, Indonesia and the Philippine Islands, produce almost 80 percent of the world's tropical hardwood exports and together have increased their export volume of roundwood from 6.6 x 106 to 29.5 x 106 m³ in the last decade. Hardwood, and especially tropical hardwood, cut for industrial use represents only a small proportion (27 percent) of the total hardwood felled, with by far the greatest volume being used for fuel. However, the industrial cut is a highly selective one, dominated in many countries by a few well-known and commercially accepted timbers. Thus, the extent to which the forest is worked over is out of all proportion to the volume of timber removed for industrial use; this, in itself, might not matter, but commercial extraction, even on a highly selective basis, often makes the forest accessible to the farmer or crop planter and leads to its further degradation or destruction.
Concern has been expressed, and rightly so, on two main counts. First, that the rate of forest loss must be slowed and, second, that the policy of highly selective species exploitation must be modified, if both long-term botanical and commercial interests are to be respected. How can this be done? One answer is to utilize a far greater proportion of the forest which means a much greater number of species of timber. This is an answer which has been given on numerous occasions and over many years, but with a few noteworthy exceptions has yet to be realized. Why?
Clearly, there is a complex of practical considerations which have contributed to the situation, but there is an underlying philosophical aspect which is believed to be important and which perhaps has not received the consideration and discussion it warrants. Timber selection for use is species oriented, sometimes on the basis of traditional use, but more frequently on considerations of availability, cost, size and performance. The relative importance of these four factors is arguable but performance or, more strictly, an appropriate combination of technical properties is often among the last to be considered.
When a timber is no longer used, usually because of cost or difficulties of supply, another is sought often on the basis of comparability with that formerly used and most frequently from among those already commercially known. This is commonly a matter of expediency but even when promotion of a timber is extended over a period of time, its acceptance is far from certain and the costs involved are often considerable. This stems from the need to integrate the unknown with the current species in use, where it must be shown to perform at least as well and perhaps even more favourably and at an acceptable-which usually means lower-cost compared with the preferred timbers. This is a difficult task in the face of a determination by many users to persist with the known rather than risk the unknown.
A further contribution to an emphasis on species selection has been the form in which much timber information has been presented. Handbooks giving information on world or national timbers invariably follow a species classification. The publication of such handbooks detailing the results of systematic testing of physical and technical has undoubtedly contributed to the more efficient and economic use of many timbers, but it has contributed also to the perpetuation of a system where species is compared with species and substitution sought in terms of comparability between species. It is this emphasis on species description and selection for use - and many major user countries have produced such information - which has favoured the known compared with the less familiar and obscured the need to provide guidance on property needs appropriate to end use.
In complete contrast to the volume of information about timber species is the very limited information available on the property requirements for end use, and yet this must be the only sound technical basis for timber selection. Currently we are, at Princes Risborough Building Research Establishment, attempting to remedy this need so far as the United Kingdom is concerned and, in so doing, provide a guide on species selection for the benefit of all concerned with timber, whether producers, specifiers, processors, or users.
An end-use property classification defines for each type of timber product the properties of significance and their levels such that timbers meeting these property requirements can be expected to give a satisfactory performance both in manufacture and use. The properties selected and levels proposed are a matter of judgement, based on experience of the factors affecting performance, and guided by specifications or standards where these exist for an end product.
In developing the Princes Risborough classification, emphasis has been directed in the first place mainly to timber products used in building and, at the time of writing, property requirements have been defined for various types or parts of window joinery, door frames and doors, cladding, flooring and cabinet work. As an example of the classification and its format, the section dealing with windows is reproduced in Table 1.
Using the information on property requirements for a product it becomes possible to identify, from among the timbers for which detailed technical information is available, those which have the appropriate properties to the required level and can be expected to be suitable for the product. As part of the current study a sorting system, using edge perforated cards, has been developed to select timbers with required combinations of properties. It is used to select timbers appropriate to a purpose and these are listed for each of the products for which property requirements are defined; only a selection of the timbers currently available in the United Kingdom and suitable for window joinery is given in Table 2. Any such list can be added to as new timbers come on offer, always provided that adequate technical information is available to enable the selection procedure to be followed; alternatively such a property classification highlights properties for which information is needed if a timber is to be considered for a particular purpose. The end-use property classification provides the means, for the first time, for the timber producer, specifier or user to make an objective assessment of the fitness or otherwise of a timber for a particular purpose.
In a consideration of Table 1, there are a number of points which warrant comment. The properties for which levels are quoted are those usually assessed in a physical and technical appraisal of timber; the descriptive terms used for levels of performance, in most instances, correspond to those adopted in the British literature, notably the handbooks and other publications issued from the Princes Risborough Laboratory. The properties of significance and the levels within them are summarized briefly as a note to Table 1.
A second and very important point concerns the levels of performance quoted. As the classification system developed, it became evident that it is both unrealistic and unhelpful to base the requirements for each property on a single performance level, thereby creating, in effect, a single performance specification. Clearly there is a need for a specifier or manufacturer to have a freedom of choice, bearing in mind the conditions and duration of use for a product and the facilities available for its manufacture. Thus, qualification is needed in two ways. In the first, the preferred level of performance is obtained but only with some additional processing requirements; thus acceptability depends on the combined cost of the selected timber and additional processing compared with the cost of a timber where the additional processing is not required.
In selecting for windows, an example is the choice between a timber rated moderately durable or better for which preservative treatment is not necessary and one of lower durability and requiring treatment; another example is between a timber which does not rapidly blunt high-speed cutters and one which is abrasive and for which tipped cutters are needed. In these examples if the cost of preservative treatment or of using tipped cutters can be justified in relation to other costs, then a more perishable timber in the one case and a more abrasive timber in the other can be accepted. In these examples there is no lowering of performance in use but in other instances a less exacting standard can be accepted and this is the basis for the second qualification to the proposed levels of performance. To meet this option, the "preferable level" for a property is varied to give an "acceptable level" which, though lower, is nevertheless considered to give an adequate performance for many conditions of use.
In adopting such a system, the listing of a timber for a particular purpose must indicate for each property whether it is met at the preferable level, at the preferable level after some modification in processing, or at the acceptable level. An example is given in Table 2 where timbers are listed which are suitable for windows. Each reaches the preferable level for all properties except those indicated by a code number; for these the preferred level is met with modified processing if the number is in brackets and the remaining numbers indicate properties reaching an acceptable level.
Properties of significance and property levels are quoted with respect to the conditions prevailing in the United Kingdom. Clearly considerable differences can be expected in preferable levels, especially for properties affecting performance, for a product used in a tropical as distinct from a temperate environment, and some difference could well occur in requirements for such properties between use in the maritime U.K. and parts of continental Europe. It is a matter of some interest, therefore, to examine on an international basis the effect of differing national standards or requirements with respect to performance and processing on property needs and levels. For this purpose an agreed terminology for defining levels within a property becomes essential.
AT AN INDONESIAN SAWMILL - putting the end first makes sense economically
Further, it should be stressed that the system, by defining property levels, provides a means of selecting species for a particular purpose. On occasions it has been described as end-use grading but end-use classification is a preferred descriptive term as it in no way replaces or dispenses with the need for conventional grading requirements. The two procedures, end-use classification and timber quality grading, combine for end-use marketing, when, it is to be expected, quality grading will be such as to meet the special needs of the end product.
PROPERTY CLASSIFICATION FOR WINDOW FRAMES, SILLS, CASEMENTS AND SASHES
TABLE 1 (Property requirements and levels)
|
Property of timber |
Preferable levels |
Acceptable modifications |
Concerning the properties * |
|
1 Natural durability (i) |
Moderately to very durable or perishable or non-durable treated according to Preservation table (ii) |
- |
1. DURABILITY. Based on the life of heartwood when in contact with the ground in temperate climates and classified in the following five grades. Very durable (more than 25 years); durable (15-25 years); moderately durable (10-15 years); non-durable (5-10 years) and perishable (less than 5 years). All sapwood is classed as perishable. |
|
2 Density |
Softwoods averaging not less than 450 kg/m³ |
Softwoods averaging 70 kg/m³ (iii) |
2. DENSITY. At a moisture content of 12 percent. |
|
3 Dimensional movement |
Small |
Medium |
3. DIMENSIONAL MOVEMENT. Classified as small, medium or large. |
|
4 Grain |
Typically straight or shallowly interlocked of which the general direction is straight |
Typically interlocked of which the general direction is straight |
4. GRAIN. Classified descriptively as typically straight or interlocked etc. |
|
5 Drying rate |
Rapid to moderate |
Fairly slow to very slow (iv) |
5. DRYING. Drying rate is classified as rapid, fairly rapid, moderate, rather slow, slow, or very slow. |
|
6 Tendency to checking during drying |
Absent or controllable |
- |
6. TENDENCY TO CHECKING DURING DRYING. Classified as absent, or controllable or present. |
|
7 Tendency to distortion during drying |
Absent or slight |
Moderate (v) |
7. TENDENCY TO DISTORTION DURING DRYING. Classified as absent, slight, moderate or severe. |
|
8 Blunting effect on cutters |
Slight to moderate or severe if tipped cutters in use |
- |
8. BLUNTING EFFECT ON CUTTERS. Classified as slight, moderate or severe. |
|
9 Machining |
Satisfactory or satisfactory with modified cutting angle |
- |
9. MACHINING. Includes sawing, planing and other cutting operations and classified as satisfactory if an acceptable surface for the utilization can be obtained. |
|
10 Tendency to resion exudation |
Absent or infrequent after drying |
See Note (vi) |
10. TENDENCY TO RESIN EXUDATION. Classified as absent, infrequent or present. |
|
11 Tendency to corrode metals |
Absent or present only if adequately protected fixings are used |
- |
11. TENDENCY TO CORRODE METALS. Classified as absent or present. |
|
12 Staining contact with metals |
Absent or present if avoidable |
Present if visually acceptable |
12. STAINING IN CONTACT WITH METALS. Classified as absent or present. |
|
13 Staining of adjoining materials by leaching of colour |
Absent |
Present only if not objectionable in particular situation |
13. STAINING OF ADJOINING MATERIALS. Classified as absent or present. |
|
14 Texture |
Fine to medium |
Coarse (vii) |
14. TEXTURE. Classified as fine, medium or coarse. |
(i) Classifications refer to durability of heartwood and exclude all sapwood.
(ii) Preservation Table.
(iii) Timber of average density below "Preferable levels" especially tropical hardwoods of wide density range and softwood below 420 kg/m³, should be used only with careful attention to screw-thread length and automatic screw driving techniques, it is not recommended where frequent careless usage may occur.
(iv) Not included in "Preferable levels" because of risk in commercial practice of uneven drying through thick cross-sections; with strict application of correct drying techniques, performance will equal that of more rapid drying timbers.
(v) In conjunction only with "Small movement" classifications.
(vi) Acceptability depends on finish to be used and visual standards required.
(vii) For exterior use, timbers with very coarse texture are the least satisfactory for painting and varnishing; an exterior wood stain is the most appropriate treatment.
This table provides general guidance on suitable methods of preservation for timbers of low durability to improve their service performance to the required level.
|
Natural durability |
Treatability |
|||
|
Permeable |
Moderately resistant |
Resistant |
Extremely resistant |
|
|
Perishable or non-durable |
Immersion (soft - wood only) |
Double vacuum |
Double vacuum |
Not acceptable |
Alternatively to what is indicated in the above Tabby, any species of timber pre-treated by the boron diffusion process gains in durability.
*For a more complete treatment of these properties, see the introduction to Handbook of Hardwoods 2nd ed. (Her Majesty's Stationery Office, London 1972) and the Handbook of Softwoods (Her Majesty's Stationery Office, London 1957).
How, it might be asked, does such a development lead to the more efficient use of the world's timber resource? The answer is by its contribution to the development of a system of marketing timber for end use rather than by a commercial name. It has been emphasized that an end-use classification recognizes timbers appropriate to particular end uses and when combined with specifications concerned with timber quality and size, the technical requirements for end-use marketing are met. With end-use marketing a consignment may comprise a single species, and indeed would need to where appearance is a matter of importance. But for many timber species appearance is of little significance and mixed species, provided that they meet certain common requirements with respect to performance and processing, could then be marketed together. It is the prospect for marketing mixed species which offers scope for the more effective use of the tropical forest resource.
A common problem in the marketing of many tropical timbers is their sporadic occurrence necessitating a sorting and collecting procedure if an adequate consignment is to be obtained, and even then unless a regular supply is forthcoming promotional activities can come to nothing. Too often in the past technically promising timbers failed to become established because adequate supplies could not be maintained. Now, with the-introduction of end-use marketing, such timbers can be grouped with others-that have the same combination of properties and the deterrent to their being cut and the problems in making available regular supplies are much reduced. But there is a further advantage in end-use marketing in that for many purposes botanical identity could cease to matter to the timber specifier or user; propaganda or promotional activities by the timber supplier to establish a "new name" - often a frustrating procedure - no longer arises in the knowledge that timber shipped for a purpose is appropriate to that use. The concept of mixed species used for an end purpose is not such a novel idea as it might appear at first sight and a number of examples of its application can be cited: for example, marine ply to British Standard 1088 is made from a range of species meeting a required natural durability level and much general purpose plywood from Malaysia and some from west Africa is marketed according to face colour (red or white) and not species, with commonly different and often a wide range of species in the core. Mixed west African redwoods have been used for parquet flooring, and mixed hardwoods, often of Malaysian origin, for such purposes as upholstered parts of furniture. Current ideas on the use of both softwoods and hardwoods for structural purposes are directed toward the development of strength groups and marketing to performance levels.
TABLE 2. - Timbers suitable for window joinery
|
The following timbers available in the United Kingdom are among those suitable for window frames, sills, casements and sashes. No timber meets the preferable level with respect to every property given in Table 1. Those where attention is required are indicated by numbers corresponding to the property list. Numbers in parentheses indicate a process modification to reach a preferable level and numbers not in parentheses indicate acceptable modifications as given in Table 1. Afrormosia (Pericopsis elata) 4, 5, (9), 12 |
It is emphasized that classification and marketing for end use make the need for reliable technical information on a species more rather than less important, unless it is to be used for a non-demanding purpose. This is because the sawmiller, or other processor, must ensure that the timbers he markets for a particular purpose have the required technical properties. This point is made because in many and probably most of the tropical hardwood forest areas much remains to be determined concerning the properties of the so far little-used or unused species and this is a first priority for more efficient exploitation and the introduction of end-use classification and marketing.
Finally, the concept of end-use marketing has to be seen in the light of likely developments in timber production and supplies. Marketing for end use and a shift in responsibility for timber selection to the primary processor are in accord with the likely development and demands for increased processing in the countries of timber production. As this develops, so clearly does the need for a greater awareness of the end uses to which the timber is to be put and the property requirements for these end uses. And, although it may take some time, sooner or later wooden components, manufactured for overseas markets and to performance levels demanded by those markets, will be produced. It is not, after all, such a far cry from blockboard to flush doors and if flush doors why not other joinery, windows, etc. and parts of furniture?
Such changes in commercial practice are some way off and, in the meantime, there is an increasing awareness that current practices with respect to the production and supply of timbers must be moderated if the forest is not to be destroyed at an unacceptable rate, especially in those regions of the world supplying a large part of the international trade in tropical hardwood. There is no simple or single way to reduce the rate of destruction of the forest, but it is suggested that the proposals made here represent a contribution to its more effective use.
Firstly, defining property needs for different end uses contributes to a more effective selection and to economy of timber in use, and secondly, by developing end-use marketing, species currently unused or under-used, instead of being left in the forest and thereafter commonly destroyed, might be brought into use and so reduce rates of forest exploitation and loss.
