- Site Admin
- Posty: 2193
- Rejestracja: 20 lut 2006 13:43
- Wpisz jaki mamy teraz rok.: 0
- Lokalizacja: Warszawa - Climate zone 6B
http://www.inbar.int/publication/txt/IN ... t_No20.htm
Technical Report 20
DESIGNING AND BUILDING WITH BAMBOO
Jules J.A. Janssen
International Network for Bamboo and Rattan
[Matter for Page 2 (second cover)]
International Network for Bamboo and Rattan
The International Network for Bamboo and Rattan (INBAR) is an intergovernmental organization established in 1997 by Treaty. As of January 2000, 21 countries (Bangladesh, Benin, Bolivia, Canada, Chile, China, Colombia, Cuba, Ecuador, Ghana, India, Indonesia, Malaysia, Myanmar, Nepal, Peru, The Philippines, Sri Lanka, Tanzania, Togo and Vietnam) have signed the Establishment Agreement. INBAR's mission is to improve the well being of producers and users of bamboo and rattan within the context of a sustainable resource base by consolidating, coordinating and supporting strategic as well as adaptive research and development. INBAR programs link partners from the government, non-government, academic and corporate sectors with knowledge and technologies that directly improve the well being of people in developing and developed countries.
INBAR publishes an ongoing series of Working Papers, Proceedings and Technical Reports, occasional monographs, reference materials and the INBAR Newsmagazine. It also provides an on-line library featuring relational databases on bamboo and rattan products, organizations, projects, experts and scientific information.
Financial support for INBAR's programs is provided by the Governments of China and the Netherlands, the International Development Research Centre (IDRC) of Canada and the United Nations International Fund for Agricultural Development (IFAD).
Anyuan Building No. 10, Anhui Beili, Asian Games Village
Chaoyang District, Beijing 100101, People's Republic of China
Tel: +86 (10) 64956961, 64956978, 64956982
Fax: +86 (10) 64956983
Branch Box 115, P.O. Box 9799, Beijing 100101, People's Republic of China
[Matter for title page. Please follow INBAR?s new House Style & Format set]
DESIGNING AND BUILDING WITH BAMBOO
Technical Report 20
Jules J.A. Janssen
Technical University of Eindhoven
Eindhoven, The Netherlands
© International Network for Bamboo and Rattan 2000
All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording or any information storage and retrieval system, without permission in writing from the publisher.
The presentation of material in this publication and in maps that appear herein does not imply the expression of any opinion on the part of INBAR concerning the legal status of any country, or the delineation of frontiers or boundaries.
Design and production
In the 26 years of working with bamboo, I have met several good people, working in the field of bamboo, from all over the world. Many of them have become my cherished friends. First among these are those from the National Bamboo Project (later Funbambu) in Costa Rica; I could list enough names to fill up this page. Apart from these Costa Rican friends, I will mention here only four people: Wim Huisman, my professor and first promoter; Walter Liese, who was a member of my Ph.D. committee and with whom I have spent many enriching hours working on bamboo in several places; Ramanuja Rao, with whom I have had as close a working relationship as two scientists can have; and Arun Kumar, who has done a tremendous editing work on the typescript of this book. I would also mention here that this book would never have been written but for the understanding and support of my wife Loek.
Over the past few years, several friends and peers had suggested that I write a book on building with bamboo. Each time such a suggestion was made, I used to recall the wise words of a professor who was famous for his lectures. Whenever pressured to write a book based on his brilliant lectures, he used to decline, saying: "If I present my lectures, my students will hear also my uncertainties, my doubts, the limits of science; but if I were to write them down, then these are exactly what would become invisible."
Then, why did I write this book now? There were some very persuasive arguments from certain quarters in favor of writing. One was that the insights and knowledge on bamboo collected during my 25 years of research, guidance of projects and visits to bamboo growing countries all over the world should not be allowed to go unrecorded. Another was that other areas ? timber, for example ? too started in a similar way with one author writing a book while the area was still small enough to be captured by the efforts of one. Finally, I thought that some information contained in my large collection of gray literature should be revealed to all interested researchers.
This book has its origin in an e-mail I received in December 1996 from the Hawaii Chapter of the American Bamboo Society, with an invitation to present a series of lectures on all aspects of bamboo. An exchange of ideas followed through several e-mails about the scope of the lectures, the topics to be covered and the time to be spent on each. It was decided an emphasis should be laid on bamboo?s mechanical properties, joints and structures. I spent a considerable part of January-June 1997 on the preparation of lecture materials and charting out the course.
I reached Hawaii in July, and spent the first two weeks presenting summaries of the lectures in three minor islands. On the third week, on the Big Island, the tempo really picked up. The event started with a demonstration on bamboo jointing to a large audience. This was followed by a three-day seminar, with six hours of lectures each day, involving a large group of participants whose enthusiasm and dedication were contagious. Over 150 people had assembled there, paying on their own for travel and accommodation, and listening to lectures on bamboo six hours a day for three days!
The effort that went into the preparation of that lecture series culminated in this book. It took some time to bring the lectures into the shape of chapters, but doing that has given me a great sense of satisfaction. I hope the readers will find this result of my endeavors useful and interesting. I thank the Hawaiian Chapter of the American bamboo Society without whose invitation to lecture this book might never have been.
Although the emphasis here is on designing and building with bamboo, I have included two chapters ? on Technology Transfer and Job Creation ? so that the publication provides a wider perspective on bamboo. I believe that this should be so because bamboo is not just a plant or just a material; in many part of the world, bamboo is a vital part of the living heritage that links yesterday with tomorrow.
Jules J.A. Janssen
The Bamboo Plant
Bamboo in its Setting
The Structure of Bamboo
Is Bamboo Economically Competitive?
Uses of Bamboo
Forests, Homesteads and Plantations
Ecological Aspects of Bamboo Plantations
3 DURABILITY AND PRESERVATION
Bamboo and Preservation
4 MECHANICAL PROPERTIES
Bamboo, a Hollow Tube
Nature?s Structural Design
Bamboo and Shear Stress
Wind Load on Bamboo
Bending vs. Shear
Rules of Thumb
5 MODELLING AND CALCULATIONS
The Art of Modelling
Design of Joints
Building on Tradition
Classification of Joints
Theory of Joints
7 INTERNATIONAL STANDARDS
The Relevance of Standards
Towards an International standard
8 BAMBOO AS REINFORCEMENT
Fiber Reinforced Cement Mortar
Bamboo Reinforcing in Concrete
Bamboo for Formwork
9 BAMBOO HOUSING
Guidelines for a Housing Project
10 TRANSFER OF TECHNOLOGY
11 JOB CREATION
Bamboo and Sustainable Development
Bamboo and Employment
12 COSTS AND BENEFITS
The Bamboo Plant
In their natural habitat, bamboo plants grow from seeds or rhizomes. The rhizome system is very important to bamboo. As bamboo does not have a central trunk as in trees, the rhizomes provide the foundation. McClure (1966) has described the bamboo rhizome as a segmented (with nodes), complex subterranean system. Bamboo rhizomes can be broadly classified as pachymorph (sympodial) or leptomorph (monopodial). In pachymorph rhizome system, the apex of a rhizome gives rise to a shoot that grows into a culm, the woody stem of bamboo. Such culms grow close together as a clump. In leptomorph rhizome system, the lateral bud from each internode develops into a culm or a rhizome. As the apex of the rhizome grows horizontal to the ground, the clump of monopodial bamboos has a spreading habit, with each culm growing at a distance from the other.
Fig. 1: A young bamboo shoot ? outside (left) and inside (right)
(From CIBA review, 1969, No. 3, p. 7; by permission of the Company Archive of Novartis AG, Basel, Switzerland)
Fig. 1 shows on the left a young shoot, protected by a series of sheaths, which will fall off as the shoot grows into a mature culm. In many cases, these protective culm sheaths are covered with tiny hairs sharp enough to pierce human skin and, in several species, toxic enough to cause skin irritation. Most bamboos are hollow, as can be seen in Fig. 1 (on the right). In the hollow inner area, some horizontal partitions called "diaphragms" can be seen (towards the bottom on the right-side picture). On the outside, these partitions are denoted by a ring around the culm. A diaphragm and the ring on the outside together form a "node". Branches grow from these nodes. The part between two nodes is called an "internode". The internodes of most bamboos are hollow; that is, they have a "cavity". The wall of the culm is called simply the "culm wall" (Fig. 2).
Fig. 2: The parts of a culm
(1 = diaphragm; 2 = ring; 3 = node; 4 = internode; 5 = culm wall; 6 = cavity)
In general, bamboo species have luxuriant foliage: the plant is one of the top producers of biomass, producing about 10 tons per hectare. According to an estimate, bamboo accounts for one-quarter of the biomass in tropical regions and one-fifth in sub-tropical regions.
Bamboo in its Setting
Fig. 3: Bamboo in landscaping (Japan)
Bamboo has the remarkable ability to create an "ambient", in the artistic sense of the term. Fig. 3 shows how bamboo can set the tone of a landscape. It forms a marvellous contribution to the beauty and an improvement to the environment (bamboo?s role in the environment will be discussed in detail in Chapter 2). The beautiful composition of leaves and culms, often in rich colors, has inspired poets and painters from the ancient to the modern times. In many modern shopping centers and office buildings around the world, bamboo?s stately elegance makes it a cherished component of architectural design. A harsh winter can severely harm bamboo because it is a plant for tropical and sub-tropical environs. But even in countries with cold climates ? such as the Western European nations and the US ? bamboo can be found in many gardens and parks as the bamboo lovers in these places seem to have developed an instinct for growing species that can survive cold winters.
A bamboo grove or plantation can be looked at as the production site of a building and engineering material; but it is also a haven for the living. Many birds build their nests on bamboo, and one can easily meet among bamboos animals like an iguana or an armadillo, or the smaller ants, snakes and scorpions. In a forest setting, larger animals such as panda, orangutan and elephant frequent bamboo stands. Some rare flowers, herbs and mushrooms can be found inside bamboo groves, the edible "princess fungus" that contains 21 amino acids being one example.
Fig. 4: The root system of bamboo (the white scale is 150 mm long)
One must not forget to adequately emphasize bamboo?s role as a means for erosion control, riverbank protection, landslide prevention and land rehabilitation. Bamboo?s extensive network of rhizomes and roots binds the top one foot of soil, which is critical for land productivity (Fig. 4), and effectively resists erosion by forces of nature such as wind and water. There are cases reported wherein bamboo was planted to successfully prevent the erosion of a riverbank and thus protect a village from being washed away. When the bamboos had grown, not only the village was safe but also the villagers were able to sell the culms and make a profit (Singh 1995).
Fig. 5: Sasa bamboo, the green cover
There are some species of bamboo that can very effectively provide a green cover for the earth and protect the soil. Sasa bamboo (Fig. 5), for example, is about 100-200 mm high and is ideal for covering an area to protect it from erosion and sunburn. Its numerous roots keep the soil together, while its leaves protect the soil against the sun. It will also improve the soil through the biomass produced: the blanket of fallen leaves is effective mulch to keep the moisture in and an organic fertilizer to rejuvenate the soil.
Fig. 6: A field in Costa Rica being readied for bamboo propagation
While most plants are multiplied by seeds, bamboo is an exception. In general, plants flower at least once a year to produce seeds. But most bamboos flower rarely ? once in a period varying from 15 to over 100 years. It is not practical to wait that long for propagation and therefore, bamboo is propagated mainly through cuttings. One place where green culms are extensively used for cuttings is Costa Rica (Fig. 6). Here, green culm lengths, with branches trimmed, are put horizontally on the soil. After 2-3 weeks, new sprouts start to grow at nodes, where a branch has been trimmed. Each sprout will have a root growing downwards and a shoot upwards. After some time, the original culm can be cut into pieces and all young sprouts replanted in a nursery. In Asia, culm cuttings are two or three internodes long. These are planted vertically into the soil, with one node deep into the soil. Roots will start growing from the lower node, and branches will sprout from the upper ones. Other methods that are in practice in different parts of the world include offset method, rhizome method, layering, macroproliferation and tissue culture.
The Structure of Bamboo
The microstructure of culm wall can be seen in Fig. 7. The outside of the culm wall (left side of the picture) is dense, as can be seen from the dark color, and only about a quarter of a millimeter thick. This layer contains much silica, a good material to protect the plant, but a nuisance for tools as silica blunts their sharp edges within a short time. The dark spots, decreasing from left to right in the cross-section, are cellulose fibers together with vessels. Cellulose acts as reinforcement, similar to steel bars in reinforced concrete or glass fiber in fiber-reinforced plastic. These fibers are concentrated near the outside. The stiffness (the resistance against bending) that this distribution pattern creates is ten percent more than the one that a more even distribution pattern could offer ? an excellent example of the structural design acumen of Mother Nature (imagine a steel tube with high tensile steel on the outside and normal mild steel on the inside!). The vessels take care of the transport of liquids during the life of the bamboo. The material between the dark spots is called "parenchyma", and it is the matrix in which the fibers are bedded (like the concrete between the steel bars). Approximately, a bamboo culm has 40% fibers, 10% vessels and 50% parenchyma.
Fig. 7: The structure of bamboo (specimen size is 6 x 6 mm)
While inspecting the structure of bamboo, one aspect readily catches our attention: bamboo does not have any "rays" like the ones present in wood (best seen in woods like beech as dark spots on the surface of a sanded plank). Rays are places for the transport and storage of food, mostly sugar, but they weaken the material. Consequently, bamboo is stronger than wood, especially in shear (this will be discussed in detail in Chapter 4).
Is Bamboo Economically Competitive?
There are several plantations in bamboo-growing countries where bamboo is harvested just like timber (Fig. . However, can one expect bamboo to be as economically competitive? A simple calculation will explain this. Assume the approximate price of an 8-meter bamboo culm to be US$ 1.50. If the volume of woody material in the culm ? taking into account only the culm wall and not the cavity inside ? is calculated, this price would be US$ 105 per cubic meter. It has been verified that because of its hollowness, bamboo's effectiveness as a beam is 1.9 better than a wooden beam. Hence, for wood to be economically as competitive as bamboo, it should not cost more than US$ 105 ¸ 1.9 = US$ 55 per cubic meter. However, wood used for beams costs much more than this, emphasizing the competitiveness of bamboo in structural use.
Fig. 8: Harvested bamboo culms in a plantation in China
In most of the bamboo-growing countries, trade in bamboo culms is well established. For example, about 25 million bamboo culms arrive every year in the dock seen in Fig. 9 from the northern part of Bangladesh. These come as rafts floating down the river, a transportation process that lasts about three weeks. During this time, the transportation crew lives in the hut set up on top of the raft. Fig. 10 shows a regular wholesale market where the bamboo culms traded. Here, culms are segregated according to their thickness, straightness, etc. for sale to building contractors and others.
Fig. 9: A dock near Dhaka, Bangladesh, from where bamboo culms are transported
Fig. 10: A wholesale bamboo market near Dhaka, Bangladesh
When considering a material for structural use, the first question that arises is about its safety. Fig. 11 shows a comparison between bamboo, timber, steel and concrete in terms of their behavior under stress. The stresses, with the symbol " " (pronounced "sigma"), are plotted on the horizontal axis. To make stresses between these different materials comparable, the value of the stress in the material when the building is in normal use is taken as the unit. This is indicated by the term " use" (also called the "allowable stress") and is about 140 N/mm2 for steel and 10 N/mm2 for timber. In each of the three diagrams in Fig. 11, a formation like a hill can be seen. This is the area of stresses at failure during tests, the middle part of the "hill" indicating the mean stress at failure (denoted by " mean"). Each hill also shows an "s" value, which is the standard deviation indicating whether the results of a test are widespread or not. Technicians consider the stress under which 5% or 2.5% of the specimens fail as the limit, and the allowable stress shall be at a safe distance below this limit. These limits are indicated as 5% or 2.5%. On the vertical axis, we see the value "p", which is the chance that a stress will occur. If a hill is wide and flat, the "p" is low; if a hill is narrow and steep, the "p" is high.
The lowest diagram is for steel, a material that is produced using a very controlled process and hence, bad specimens are very rare. It shows a narrow and steep hill, indicating that failure under stress occurs in a narrow range indicated by a small value for "s". This means that the allowable stress (" use") can be at a short distance from the stress at failure. The diagram in the middle for wood and bamboo, which are natural materials, shows a wide variety of stresses around the mean stress at failure. In these materials, specimen quality varies widely from very bad to very good. Because of this uncertainty, one finds a large distance between the stress at failure and the allowable stress. The top diagram is for concrete, which is between the other two as far as safety is concerned. In normal circumstances, the use of steel is economical because of the short distance between allowable stress and stress at failure, signifying the optimum use of the material. The use of timber and bamboo, on the other hand, is less optimal since the allowable stress is very low compared when with stress at failure.
Fig. 11: A comparison of safety of bamboo and other materials
In the case of a disaster like a hurricane or an earthquake, however, the stresses will get multiplied. They may become double the allowable stress. In such cases, stresses in steel will come into the area of failure, but not in timber and bamboo. This means that steel structures will suffer much damage, while most structures of timber or bamboo will remain in good condition. A bamboo house is a good place to stay during a hurricane or an earthquake (provided the house has been built with proper care).
Fig. 12: Strength and stiffness per weight
Another comparison between the materials is shown in Fig. 12. Two questions are dealt with here ? how much strength and how much stiffness (resistance against deformation) does concrete, steel, timber or bamboo give? The diagram shows that, as far as strength is concerned, concrete is the worst, followed by timber (the green bars in the diagram are calculated as the strength divided by the mass per volume or the density). Steel is the best and bamboo the second best. In terms of stiffness, the fourth place is for concrete, third for timber, second for steel and the first place is for bamboo (the brown bars in this diagram are calculated as the E-modulus divided by the mass per volume or the density).
Mechanical properties will be dealt with in detail later, and the following is only a short introduction. The most important mechanical property is the mass of the material per unit volume (which is the density) expressed usually in kg/m3. For most bamboos, the density is about 700-800 kg/m3, which varies with the quality of the site of growing, the species, the position in the culm, etc. Why is this property important? The greater the mass per volume, the heavier the bamboo because more molecules are present in unit volume. In other words, the greater the mass per volume, the denser the material. Evidently this results in properties that are desirable in most situations. This relation between mass per volume and strength gives some rules of thumb. For instance, the bending stress at failure (in N/mm2) can be estimated as being 0.14 times the mass per volume (in kg/m3).
Fig. 13: Bending tests for bamboo (Technical University of Eindhoven)
A notable feature is that failure in bending of bamboo is not a failure. This seemingly illogical statement needs an explanation. If a bending test is performed on a beam of timber or any other building material, first a "crack" develops and then the beam breaks into two pieces ? a real failure. Bending tests, such as the long-term bending test shown in Fig. 13, were performed at the Technical University of Eindhoven from 1981 till 1988. The tests showed that "creep", which is increasing deformation on the long term, does not occur in bamboo, while most timbers are well known for this.
Fig. 14 shows a bamboo after "failure". If the specimen was a timber beam, it would have cracked and broken into two. In bamboo, however, all fibers along its length still exist without any damage. The only thing that has happened is that the bond between the fibers has broken down and, consequently, the circular form of the cross-section has lost its strength. Remarkably, if the load placed on it is taken away, the bamboo specimen will return to its original straight form. This phenomenon has great practical importance. If a bamboo house has suffered from a heavy earthquake, some bamboo elements in it might show damage like this. But the house will still be standing and habitable! Some temporary repair measures ? such as winding a rope around the damaged bamboo ? are all that would be required till the damaged posts or beams can eventually be replaced.
Fig. 14: Failure in bending for bamboo (Technical University of Eindhoven)
It was mentioned earlier in this Chapter that bamboo is stronger than wood in shear. Fig. 15 shows a test on shear, performed in Costa Rica, according a test method developed at the Technical University of Eindhoven in the 1970s. Shear is important in joints to connect one bamboo with another. Nails, bolts, pins and similar fasteners are used in such joints. In all these joints a hole is made in the bamboo, and the fastener is put trough this hole. When in use, a tensile force from this fastener will be applied towards the end of the bamboo joint, resulting in shear. The test method in Fig. 15 has been selected as the best after a long series of comparisons among different test methods (it is also an excellent example of North-South technical cooperation!).
Fig. 15: Test on shear (Technical University of Eindhoven)
Uses of Bamboo
Bamboo can be put to thousands of uses. Since most of the trade in bamboo articles happens on the informal market, annual value of the global trade in bamboo products is difficult to determine. However, a conservative estimate puts it at US$ 10 billion. This section will examine some of the major uses of bamboo.
Fig. 16: Bamboo scaffolding on a building in Shanghai, China
Bamboo scaffolding is a rich tradition in many Asian countries such as China, India and Thailand. Bamboo scaffolding is well known for its capacity to resist hurricanes. Cases are known wherein bamboo scaffolds survived hurricanes that blew away steel ones as if they were matchsticks. Bamboo scaffolding now is suffering from competition with steel scaffolding, because the latter is an industrial product with standardized dimensions, which make it quick to erect and dismantle. In this respect, bamboo scaffolding needs some technical upgrading. There are some aspects that resist development. For instance, in most cases, the labor force that puts up scaffoldings is organized in guilds that are closed to people who do not belong to certain families. This structure is a guarantee for good transfer of traditional knowledge but a major obstacle for bringing in modern developments.
Bamboo is a superb option for good and cheap housing. Fig. 17 shows one of the 1987 prototypes of the National Bamboo Project in Costa Rica. It is an example of good design: overhanging roof, a structure of bamboo culms, walls of panels of split bamboos with cement mortar on both sides, and ventilation through the upper part of the walls (this building method was later simplified and improved). The use of bamboo in housing is discussed in detail in Chapter 11.
Fig. 17: A prototype bamboo house in Costa Rica
The capacity of people to invent their own solutions for difficult problems plays an important part in development. Fig. 18 shows an example of such a solution. Everybody knows bamboo should not have any prolonged direct contact with the soil, particularly wet soil. But a bamboo column needs to be anchored securely to the foundation in order to keep the house down during strong winds. The staff of the Costa Rican National Bamboo Project invented a prefabricated foundation. The bamboo column is extended at the lower end using concrete, which penetrates the bamboo for about 400 mm (the length of an internode) and extends outside the column for over 700 mm. The concrete is poured into the bamboo culm kept in upside-down position. A piece of PVC tube, cut lengthways and wrapped around the bamboo is being used as formwork. This solution is commendable because it is a simple and effective answer based on a sound analysis of the problem.
Fig. 18: Prefab concrete foundation for bamboo column
If bamboo is considered for mass housing, then it becomes necessary to look into prefabrication options. Fig. 19 shows a panel factory in Costa Rica. Imagine a situation where 1 200 houses have to be built annually, and each house needs 17 panels. This means that one panel has to be produced every six minutes, given an 8-hour shift per day and 250 working days ? really an industrial process. Most people think of bamboo as a rural commodity for the small farmer and his family. While this is true to a large extent, there is an industrial side for bamboo as well. More such industrial processes need to be developed if bamboo is to contribute towards housing the one billion homeless people in the world. It must also be mentioned that industries provide large-scale employment.
Fig. 19: Panels being prefabricated for mass housing
The last statement leads to the role of bamboo in job creation. Bamboo is a material that provides several job creation opportunities because many products can be made from it with low capital investments. The precondition for this is a social structure, mainly in the villages, that fosters cooperatives, and education and training in making bamboo products. Fig. 20 shows a chair, a good example of furniture that can be made at village level. Only simple tools are needed; more essential is a good design that takes into account not only the aesthetic value but also the way the product can be made, its durability and, most importantly, its marketability. In most cases, the last item is the bottleneck. In Europe and elsewhere some people do buy products made in developing countries, but this can never amount to structural support for the economy of bamboo-growing countries. For that, there has to be bamboo products that can compete with products made from wood or even plastic. The chair shown in Fig. 20 does not meet the standards of the markets in Europe or the United States. Unfortunately, there is a long way to go to design and develop bamboo products that meet export requirements. Fig. 21 shows a more simple item, a piece of handicraft to be sold to tourists. This really is a promising area, provided there are tourists around. Here too a good design is essential but the quality level can be lower, as tourists buy items with a less critical mind and more for souvenir value. A sound system of cooperatives is needed to ensure sure that the profit does not remain in the shop in town but reaches the people in the village who create the artefacts.
Fig. 20: Bamboo furniture (Costa Rica)
Fig. 21: Bamboo handicrafts (Japan)
Plybamboo, which is plywood made of bamboo, provides a good avenue for job creation at village level. Weaving of split bamboo strips is a fairly long tradition and in the case of plybamboo, it takes the road towards a modern industry. One unique appeal of the process is that it can still start at the village level, but end in a modern factory.
Fig. 22: Weaving of bamboo mats (India)
Fig. 23: Production of plybamboo (India)
Fig. 22 shows a group of villagers, mostly women, involved in weaving bamboo mats. They can do this on days they cannot work on their land, or during their leisure. An organization in the form of a cooperative is needed to effectively manage the work and ensure equitable distribution of profits. From a social point of view, work like this is very good for community health ? people of a disadvantaged group (women) are working together in a relaxed atmosphere to earn cash income, leading to both social and economic empowerment. Typically, at the end of the day, the woven bamboo mats are brought to a cooperative-owned factory, where the mats are glued together with an inner layer of cheap wood to make plybamboo boards (Fig. 23). This whole process will be examined more closely in Chapter 10 on job creation.
The discussion so far had focused on the suitability of bamboo both as a traditional and modern material. One important aspect that prevents the wider utilization of bamboo is its depleting resource base. Even in countries like China and India, two countries that have the largest bamboo resource base, lack of availability of the material is being acutely felt. The situation is not very different in other bamboo-growing countries. Hence, before any serious attempt to industrialize bamboo processes can be made, the resource situation needs to be improved. It has become very evident that natural propagation is not adequate to regenerate the resource to the extent needed. Active and systematic plantation programs are required if bamboo is to ever reach a utilization level that does justice to its potential.
Forests, Homesteads and Plantations
Bamboo can usually be seen growing in natural forests, homesteads and plantations. In many parts of the world, the largest stock of bamboo still grows in natural forests, the primary habitat of bamboo. The extraction of forest bamboos raises some important questions regarding resource ownership and management.
Historically, the people living in and around a forest had the customary right to harvest the bamboo growing in that forest for their use and in pursuit of their livelihood. But this custom has come to pass in most parts of today?s world. Now, almost all forests are state-owned, and agencies like a State Forest Departments have taken control over the forests with the intention of protecting them.
The taking over of forests by the state was a setback for the forest-dependent people as it meant that harvesting "their" bamboo was now restricted or, in many cases, forbidden. In some regions, a management system was put in place so that the people can obtain a permit to harvest a fixed number of culms per year from the forest. This permit was issued on payment of a fee and, as reported in several places, bribes for the forest department staff as well. A "free" resource thus became a controlled and expensive one, making bamboo-based occupations unattractive.
A major problem for bamboo stand management is that people prefer to harvest the culms at the shortest possible distance from their village. This leads to over-harvest of clumps at forest edges, while the clumps in the inner parts of the forest grow so thick that mature culms towards the center of the clump become totally inaccessible. Since "state-owned" also translates into "nobody?s property", none feels responsible for the maintenance and management of forest bamboo. One need not emphasize how detrimental such a situation is for bamboo, and for the forest as a whole.
The relationship between bamboo and the natural forest deserves special attention. For many people, this relationship might hold negative aspects as bamboo is related to human disturbance of pristine forests. As Stern (1995) says: "Chusquea scandens was significantly ubiquitous on transacts in forests with the greatest degree of human disturbance. This result was qualitatively supported by the abundance of bamboo at trail heads and near the entrance of the reserve." Zhang (1995) reports bamboo in Xishuangbanna, China, as secondary vegetation after removal of the original primary forest. Bamboo stands can extend to cover up to 70-80 % of the area below an altitude of 1 000 m.
The destruction of the primary forest is caused by shifting cultivation, or the increasing need of a growing population for farmland, fuel wood or building area. Another minor cause is the harvest of timber for export. A lack of "fair trade" plays a role as well. For example, in the Costa Rica of the old days a tractor could be paid for with 50 bags of coffee; now the same tractor requires 2 000 bags of coffee. No wonder if more forestlands come under coffee plantation!
Unregulated extraction of forest products by forest-dependent communities for their subsistence living has been ascribed as a factor for the destruction of forests. Any strategy to remedy this should be based on grassroots participation and an understanding of the basic needs and aspirations of the said communities. As most of us tend to think, they are not a minority. The indigenous groups living in or bordering tropical rainforests numbers about 700 million, while the tropical forests, bush lands and Savannah measure about 2.9 billion ha. As Stiles (1994) puts it: "Together, indigenous peoples and their traditional lands would constitute the third most populous country in the world and the eighth largest in area." Bamboo occupies an important place in this extraction system because of its wide utility to forest-dependent communities. With appropriate management, it can become a natural resource that can be used forever.
Homesteads (Fig. 24) are small areas on the lands of small farmers where some bamboo is grown for their own use. Evidently, the farmer will maintain the bamboo stand well as it is considered a part of the capital asset. The farmer family uses most of the harvest and only a minor part is sold on the local market. Bamboos from homesteads rarely reach the formal market. Preservation is an area of concern, as only traditional preservation methods can be afforded by the farmer. A local cooperative might be a solution, as it would have the capital to own the equipment required for modern methods. In most regions, however, the needed social structure is absent and consequently, modern preservation is not an available option.
Fig. 24: A bamboo homestead in Burundi
The economics of homesteads would bear a glance at this point. The following data come from an unpublished survey in Bangladesh in which the author had participated (SDC 1991). In the homestead mode of production, bamboo is calculated to give a net return of US$ 1 285 per ha, as compared with US$ 1 860 for banana and US$ 8 000 for jackfruit. In the plantation mode, however, bamboo yields a net return of US$ 2 285 per ha, as compared with sugarcane at US$ 1 430 and jute at US$ 340.
It must be mentioned here that the homestead mode turns out to be less profitable only if the farmer wants to sell the bamboo on the market. The real value of homestead bamboo lies in its utility to the farmer and his family.
An ideal place for a bamboo homestead would be the narrow strip of land along a road, a railway line or places like that. Normally such places are not put to any good use, and a row or two of bamboo (clumping type, not runners!) can provide a fair income to the family that nurtures the plant. However, the rights of property and harvest need to be well formulated before this could happen.
Growing bamboo as a plantation crop hardly comes into the realm of an individual farmer; it is a large-scale commercial activity. Plantations are owned by either companies or cooperatives. In the first category, there are several pulp and paper companies that grow and use bamboo as a raw material. These companies need huge quantities of bamboo and hence large plantations, preferably along a river connecting the plantation with the factory downstream. Allocation of such huge areas for non-food agro-industry is something that most bamboo-growing countries cannot afford. Harvesting of plantation bamboo and its processing do create several jobs in the area, but it is an unstable occupation since all people in the area will be working for one single company and there might not be another avenue for income. Unless the production of bamboo equals or surpasses consumption, such a plantation will not be viable. Then there are other probabilities such as gregarious flowering, especially when overgrazing hampers the regeneration of bamboo, which could swiftly put an end to the plantation-based local economy.
If this is compared with a plantation owned by a local cooperative, one can see a better equilibrium between the plantation on the one hand and the needs of the local population and the environment on the other. Even a large-scale plantation for pulp can be made sustainable and profitable on the long term. This requires an in-depth analysis of the needs and the opportunities of each of these four components in the process ? the management of the cooperative, the shareholders, the local population and the environment. Here too politico-legal issues about the use of public land for private income may have to be resolved, this can be a cumbersome process.
The profit is much better in the case of bamboo plantations. Dhanarajan et al. (1989) quote the following data on the profitability of a bamboo plantation in Thailand:
Year 1 2 3 4 5
Cost (US$/ha) 255 167 190 255 330
Revenue (US$/ha) - - 160 710 1880
The situation remains stable from the 5th year onwards. This profit may be compared with that of other crops to get an idea as to where bamboo stands in terms of profitability: crops such as cotton, oil palm, sugarcane and cassava give a revenue of US$ 575 per ha. At a discount rate of 13% the benefit-cost ratio is 1.90. The higher profit offered by bamboo is more from shoots (85%) than culms (15%).
Take a close look at the plantation in Fig. 25. If someone asks for a description of a factory that absorbing carbon from polluted air, you can show this picture. For this plantation is such a factory. Carbon is being absorbed from the air and stored in the bamboo, a process called "carbon sequestration". The Guadua plantations in Costa Rica were calculated to absorb 17 tons of carbon per hectare per year. One could easily recommend bamboo groves for all lung spaces in our polluted cities.
Fig. 25: A bamboo plantation in Costa Rica
The working of carbon sequestration is very simple: bamboo is composed of cellulose and lignin, and both contain much carbon. In other words, bamboo needs to take in a lot of carbon to grow. But the effect of carbon sequestration will be nullified if bamboo is used as fuel-wood, as burning will release the stored carbon back into environment. Long-term uses of bamboo, such as in housing and furniture, are ideal to ensure that the carbon stays locked in for a long period.
Ecological Aspects of Bamboo Plantations
In 1990, a thorough study was made on the environmental impacts of the National Bamboo Project in Costa Rica (Billing and Gerger 1990). They classified the impacts of bamboo on the environment as follows.
Impact of major positive magnitude
· Erosion: Bamboo grows fast, and in a short time develops an extended root system, supporting the soil and preventing it from being washed away by heavy rains (for a more details on bamboo and erosion, see Chapter 1 and Singh 1995). The dense roof of branches and leaves protects the ground from forceful tropical rains. In a bamboo plantation clear-cutting does not happen; only the adult culms are taken away, leaving the plantation intact. Bamboo is a lightweight material, without a need for heavy machinery for felling and transportation.
· Physical soil structure: The root system (Fig. 26) loosens up the soil, which was made hard and compact by exposure, machinery and cattle. The leaf roof protects the soil from further exposure.
· Ground water level: Bamboo consumes water, but this is more than compensated by the reduced evaporation created by the leaf roof, and by the layer of fallen leaves. Due to the increased permeability of the soil, water run-off is reduced, allowing more water to penetrate the soil and to remain in the area.
Fig. 26: The root system of bamboo
· Soil fertility: This is improved by protecting the soil from exposure, and by fallen leaves providing organic material. Soil fertility can be diminished by extraction of certain nutrients; this depends on the fact whether the bamboo lives in the wilderness as a monoculture or with other plants. In a plantation many culms are harvested which is likely to cause the use of fertilizers.
· Drainage by the root system and the layer of fallen leaves.
· Soil micro fauna.
· Ground water quality.
· Micro and local climate: Stabilization of humidity and temperature.
· Feeding area and habitat for fauna: Bamboo provides a rich environment for insects, birds and some mammals. Insects find sufficient food in the bamboos, and they in turn act as food for birds. For mammals in need of fruit, access to other types of forest is necessary.
· Soil micro flora, regional and global climate, fire hazard, species diversity in flora.
· Laterization of soil (pH). Bamboo Guadua is found to have a slight negative effect on the pH-level; the soil is already slightly acidic in these areas.
Another important aspect of bamboo is the biomass. The biomass of bamboo depends on the botanical species, the site quality, the climate, etc. Data vary between 50 and 100 ton per ha, divided into 60-70 % for culms, 15-10% for branches and 15-20% for foliage (Liese 1985). More detailed information is in the following table for natural stands of Gigantochloa scortechnii bamboo in Malaysia (Abd. Razak 1992):
Part Biomass (in tons/ha)
Culms 82 53
Branches 20 10
Leaves 17 9
Total 119 72
The dry matter density, the dry biomass divided by the mean height, is 72 tons/ha ¸ 13.3 m = 0.54 kg/m3.
The data given below are for Phyllostachys spp. in Japan (five different sets of data are from five different authors):
Culms (dry t/ha) 88 49 61 55 37
Branches (dry t/ha) 13 9 14 12 7
Leaves (dry t/ha) 5 4 6 5 4
Total (dry t/ha) 106 63 81 73 48
Other data are:
Density (kg/m3) 0.80 0.47 0.57 0.44 0.52
Leaf index (ha/ha) 12 9 - - 8
Density is the dry matter density, the dry biomass divided by the mean height (Suzuki 1987). These data clearly indicate the importance of bamboo in biomass generation.
Before this discussion on plantations is concluded, it is necessary to answer the question whether a bamboo plantation constitutes a monoculture. This is a matter that calls for an educated opinion. Evidently, if one compares a bamboo plantation with a natural forest, there is no doubt that a bamboo plantation is a monoculture. The richness of a rainforest is the maximum attainable. But if the comparison is with another crop plantation (bananas, for instance) or grassland, then one can see that a bamboo plantation is much more diversified. As mentioned earlier, many herbs and flowering plants thrive in bamboo plantations, which also play host to many species of birds, insects and other living beings (Fig. 27). This situation owes much to the fact that application of herbicides and similar chemicals does not form part of the normal management regime for an adult bamboo plantation.
Fig. 27: A hummingbird?s nest in a bamboo plantation in Costa Rica
The management of a new plantation starts with a market survey, the selection of appropriate species and the selection of a site. The market survey is mainly to identify the end uses to help select the appropriate bamboo species, as well as to determine the quantity requirement. The local climate also forms a factor in species selection. The site has to be selected with regard to soil quality, water, transport, labor force, etc., and there has to be a species-site matching.
The plantation work starts with clearing the site off shrubs and other unwanted vegetation, and the construction of access roads and sheds. Planting material (plants, cuttings or offsets) may be obtained from a bamboo forest, another plantation or a nursery. It is advisable to obtain planting material from different sources to insure against the possibility of losing the entire plantation to gregarious flowering. The following data from Costa Rica give the daily labor requirement for a new plantation that has 220 plants per hectare (Venegas 1996):
Clearing of land 4.3 laborers/ha
Collection of planting material 3.0 laborers/ha
Preparation of planting material 2.0 laborers/ha
Digging holes and planting 3.7 laborers/ha
Total 13.5 laborers/ha
Fig. 28: Preparing culms for producing culm cuttings (Costa Rica)
As previously mentioned, there are several propagation methods. One of the methods, used widely in Costa Rica, is the culm cutting method (Fig. 28). Whole fresh culms with branches cut off are buried in the soil to stimulate alternating buds. After two or three weeks, shoots will appear above the ground where branches have been cut off, and rooting also takes place to produce plantlets. After some months, the young plants can be removed (Fig. 29) and replanted in another place. In the span of six months, a young plantation will be flourishing (Fig. 30).
Fig. 29: A plant with well-developed roots and shoots
Fig. 30: A Costa Rican plantation after 6 months (foreground) and 12 months (background)
The daily labor requirement for the maintenance of the plantation in the first year is as follows:
Clearing shrubs, etc. 9 laborers/ha
Other work 4 laborers/ha
Weed control 3 laborers/ha
Fertilizer application 2 laborers/ha
Total 18 laborers/ha
Two liters of herbicides and four bags of fertilizer are used per hectare. The herbicides are needed only in the first and second years; in the third year, the bamboo can compete with other shrubs on its own (Figs. 31, 32).
Fig. 31: The effect of herbicides to give space for the young bamboo plants
Fig. 32: Young culms after two years
In the 3rd, 4th and 5th years, maintenance needs become much less. Harvesting starts in the 5th or 6th year. Only adult culms are harvested and the younger ones, constituting about 80%, remain. There is no clear-felling as with tree plantations. This keeps the microclimate and the environment in good shape. A well-managed plantation yields 20-30 tons (air-dry) of bamboo per ha per year; and the plantation keeps on going and growing (Fig. 33). This means that a sound marketing plan needs to be in place before first yield.
Fig. 33: A well-maintained, open plantation in China
As people become more and more environment conscious, plant nurseries have started coming up in many places. A nursery might be the easiest source for the planting material for a bamboo plantation. It would also be a good idea for an established plantation to have its own nursery. Schlegel (1994) gives the data for a Bambusa blumeana nursery in the Philippines. The assumptions are:
· Planting distance is 7 x 7 meters, 225 plants per hectare.
· For plant propagation, 270 two-node cuttings are needed (225 plus 20%).
· 23 culms have to be harvested from 3-4 different clumps; 12 two-node cuttings can be collected from one culm.
The number of workdays needed for setting up the nursery is:
Nursery construction 7 days
Collection of planting material 2 days
Preparation of planting material
(135 cuttings per day) 2 days
Soil collection and potting
(40 pots per day) 7 days
Nursery care and maintenance
(10 days/month, 4 months) 40 days
Field layout, planning holes digging,
hauling and transplanting 20 days
Care and maintenance in the first 2 years
(6 months/year, 10 days/month) 60 days
Care and maintenance for the remaining
years until harvest 60 days
Materials like plastic bags, farm tools,
fertilizer, etc. costed as equal to 27 days
Total workdays required 225 days
S.D. Thatte (1997) gives similar data for a plantation in India, with bamboo as an intercrop. Expenses in the first year are US$ 1 195 per year per hectare (price level 1996), diminishing to US$ 688 in the second year and to US$ 45 from the third year onwards. Beginning the fourth year, the harvest is 3 700 culms per hectare. With each culm selling at US$ 0.22, the total profit per year per hectare is US$ 800.
3 Durability and Preservation
The main concern of any actual or potential user of a bamboo house or product is the short durability of the material. The service life of bamboo is generally considered as being too short for any worthwhile investment. This, unfortunately, is true to a large extent. Bamboo has less natural durability than most woods, owing to a shortage of certain chemicals that occur in most woods but are absent in bamboo. Information on the natural durability of different bamboo species is still sparse. Research on the differences among various species would allow for the selection of species with better natural durability. Whether the extent of natural durability of such a selected species will meet the expected service life requirement for a particular product, however, will remain an open question.
A problem that compounds the low natural durability is the hollowness of the bamboo culm, particularly when compared with the end-to-end massive cross-section of wood. If fungi or insects attack and destroy the outer layer of wood, say to a depth of 2 mm, most of the cross-section will still be in good condition. In the case of bamboo, a loss of 2 mm may mean the loss of one-quarter of its thickness. The hollowness also offers a relatively safe hiding place for the agents of destruction.
In most tropical countries, the high relative humidity of the air adds to durability problems. A high moisture content in the bamboo ? which makes complete drying difficult and thus provides an opening for fungal attack ? poses uncertainties in its application in housing, furniture, etc.
A rough guideline on the service life of untreated bamboo is:
· 1-3 years in the open and in contact with soil;
· 4-6 years under cover and free from contact with the soil; and
· 10-15 years under very good storage/use conditions.
Preservation can improve these periods considerably.
Fig. 34: Deterioration of bamboo (the white scale is 150 mm long)
The consequence of the low durability of bamboo can be seen in Fig. 34: the wall of a hut in Bangladesh has started crumbling just after six months. The woven bamboo mat used for the wall was made from unpreserved bamboo, and the clay foundation of the hut kept the bamboo always wet. One can easily see how much the quality of the walls has deteriorated in such a short time. The fact that such bamboo houses are those built by low-income groups compounds the gravity of the problem.
Data on natural durability are scarce (Kumar et al. 1994), with most authors providing only general statements. Some reports identify a certain species as having a better durability than another, but such data are still insufficient for a classification similar to timber. People in villages know by experience the durability of the bamboos in their homesteads. The lower part of a culm is said to be more durable, and so is the outer part of the culm wall. The starch in the bamboo makes it attractive to fungi and beetles. It has been observed that the culms harvested during the dry season have a better durability than those felled in the rainy season. Also, bamboo is more resistant to insects after flowering, owing to starch depletion. The correlation between natural durability and the phases of the moon is difficult to establish; presumably, it is based more on culture and tradition than on physical reality (Kirkpatrick and Simmonds 1958).
The remedy for insufficient natural durability is preservation, be it traditional or chemical. However, the following fundamental rules can help save much trouble (and money).
Harvesting in the season when the starch content is low.
Selecting only those species that the local people have identified as better suited for the intended purpose.
Sound management in storage ? keep dry and free from the soil. Store the culms under roof, protected from rain, and in horizontal layers with sufficient room in between for air movement.
The period when the material/product is in transit from one place to another is crucial. The climate in a container during transportation by sea is perfect for most fungi and insects (Fig. 35). Hence, furniture and similar export items need to be treated before transportation. In most cases, brushing or spraying the bamboo material/product with a preservative like borax-boric acid might be adequate.
Fig. 35: Mold growing on untreated bamboo
When used in building construction, one cardinal rule is to ensure that the bamboo is kept dry. This means that it should be kept free from splashing rainwater by a watertight foundation and by an overhanging roof. Correct design of all building details is a must; no chemical treatment will be good enough to solve the problems caused by incorrect design (Fig. 36).
Fig. 36: Concrete foundation for a bamboo building, but the bamboo gets wet enough
to invite fungal and insect attacks
Despite these precautions, the bamboo used in a building might get wet. To address such a possibility, the design of the building should be one that allows unrestricted airflow to facilitate quick drying. This might be a burden on the creativity of the designer, but the effort would pay on the long term.
Only after these rules have been observed can one consider preservation in its technical sense.
Bamboo and Preservation
Bamboo is not made up in a way that facilitates preservative treatment. The outer skin, with its high silica content, forms a good raincoat and resists insects but also prevents preservative from entering the culm. The inside is covered with a waxy layer that is impermeable as well. So, a preservative can enter only through the conducting vessels, which are not more than ten percent of the cross-section. They close forever within 24 hours after harvest ? which means that preservation has to be carried out within this short time limit.
In the case of timber, preservation is carried out nearly always on sawn timber. A result of sawing is that numerous vessels and cells open up, considerably easing the penetration of any preservative. Also, timber has rays that provide cross-connections between the vessels. Bamboo is unlike timber in both these aspects.
Bamboo preservation methods fall into two categories: traditional and chemical.
In many places, traditional preservation methods ? such as curing, smoking, soaking and seasoning, and lime-washing ? are used. The real effect of these methods is not known. However, these methods are popular as they can be applied without any capital investment and with low skill levels.
For curing, the harvested bamboo culms are left in the open, with branches and leaves intact. Transpiration process, which continues even after felling, causes the starch content to fall. Smoking, treatment of the culms over fire, is effective against fungi and insects. Soaking and seasoning involves immersing the culms in stagnant or running water for a few weeks to leach out the sugars. After this, the wet bamboos are air-dried under shade. Lime-washing ? literally washing with lime water ? is reported to protect against fungal attack.
A notable example of soaking is the use of bamboo permanently under water, as in floating restaurants. Fig. 37 shows such a floating restaurant, the floor of which is made with four layers of bamboo, placed crosswise. The top layer has a service life of less than a year, but the other three are permanently under water and their lifetime is very long.
Fig. 37: A floating restaurant in the Philippines
If bamboo is to be used in modern industry or in large-scale projects for housing or other buildings, chemical methods of preservation are unavoidable. It is better to avoid preservatives with chemicals like arsenic as they pose a risk to the environment as well as to the health of those handling them. Effective and safe chemicals are based on the element boron, such as copper-chrome-boron (CCB). Chemicals like boric acid, borax and boron are cheap and effective. Good preservation has been obtained in Costa Rica with a boron-based fertilizer, disodium octoborate tetrahydrate (chemical formula Na2B8O13.4H2O), with 66% active boron content. A big advantage of using this chemical is that there is no waste at all. Once it has been used in the preservation process for some time and is mixed with starch and sugar from the bamboo, it can be applied as a fertilizer!
Two methods are available to introduce chemicals into the bamboo: modified Boucherie process for whole green culms and dip-diffusion for split culms.
Modified Boucherie process
In this method, the preservative is passed under pressure through the culm vessels till it comes out at the other end of the culm. This can be applied only to fresh bamboo, within 24 hours after the harvest. As the preservative is passed through the vessels, the remaining 90% of the cross section does not get any contact with the preservative.
The preservative liquid is kept in a closed drum, which is connected to one end of the bamboo with rubber tubes and sleeves tightly clamped around the end of the bamboo (Figs. 38, 39). An air pump provides the pressure. Air in the upper part of the sleeve has to be removed; otherwise, the upper part of the culm will remain unpreserved, resulting in badly treated culms. At first, sap will start dripping from the lower end (Fig. 40) without preservative in it. As the process continues, the concentration of preservative in the sap will increase. The process has to be continued till the whole length of bamboo gets sufficient quantity of preservative. To determine end of process, the concentration of the solution dripping from the lower end must be checked. If it nearly equals the concentration of the preservative in the tank, the process is complete. The liquid passing out of the culm may be recycled (Fig. 41) after cleaning and adding chemicals to achieve the original concentration. After treatment, the culms must be stored under shade to dry.
Fig. 38: Modified Boucherie treatment equipment: the rubber tubes and air outlets
Fig. 39: Modified Boucherie treatment in progress
Fig. 40: Sap beginning to drip from the lower end of the culm during treatment
Fig. 41: The liquid coming out at the lower end may be collected for recycling
An alternative Boucherie treatment method is to scrap the inner wall surface of the bottom-most internode of the culm, then hang the culm vertically and fill the prepared internode with the preservative. Scraping the inner wall gives the preservative access to the culm wall tissue.
In this method, the culm is first immersed (or dipped) in the preservative so that a slow penetration process (diffusion) takes place. This method can be applied only to split or sawn bamboo strips since whole culms will not allow the preservative to penetrate.
Split bamboo pieces of required size are immersed in a bath with the preservative solution, and weighed down with bricks to keep them immersed. After about 10 minutes of soaking, the bamboo pieces are taken out of the bath (wear gloves!). Excess preservative is drained into the bath. The bamboo pieces are wrapped in plastic sheets and left for one week. The sheets are removed, and the bamboo seasoned in a vertical position for one week.
The preservatives should be prepared carefully, following all instructions to the letter. This may sound as a needless remark, but it is a point that can never be over-emphasized. The author had once been involved in a preservation project in which the preserved bamboos were much more infested with fungi than the unpreserved ones. An investigation revealed that the person who carried out the process did not understand the implication of the preservative being heavier than water, and did not stir the preservative and the water well enough. Consequently, the preservative was lying at the bottom of the bath through out the "preservation process" and then just drained out. The chemicals never got a chance to get into the "
Kto jest online
Użytkownicy przeglądający to forum: Obecnie na forum nie ma żadnego zarejestrowanego użytkownika i 2 gości