Taking certain pre-conditions into account, almost the entire stem (trunk) of the coconut palm tree can be used to manufacture structural components, furniture and other utility articles.
The essential things that must be considered are:
- density group and wood structure
- the climate where it is to be used
- the woodworking conditions.
The three density groups discussed in the first chapter must be taken as a basic pre-condition in utilization. A list of recommended uses is given in Table 3.
Table 3: End-uses for coconut wood
|- studs, beams||X|
|- roof trusses||X||X|
|- gangnail trusses||X||X|
|- glulam beams||X||X|
|- floor joists||X||X|
|- internal members||X||X|
|Door and window frames||X||X|
|Wall-panelling (t & g)||X||X||X|
|Tool handles, tools||X|
|Crates, pallets, boxes||X||X||X|
|Transmission poles||round, hollow stem|
|Fence posts||quarter split, upper third of stem|
As can be seen in Table 3, wooden products are manufactured mainly from medium-density and high-density coconut palm wood. The low-density wood does not achieve adequate strength values and surface qualities and therefore has only a very limited range of uses.
Basically it is true to say that apart from a few exceptions (e.g. bentwood parts for furniture), all of the classical solid wood products can be processed from coconut palm wood. As with all other types of wood, it is necessary to take into account the fact that coconut palm wood must be dried down to a wood moisture content corresponding to the surrounding atmosphere (= a function of the prevailing air temperature and air humidity). For example this wood moisture content is about 8% for wood used in heated rooms. Such wood moisture content values are achieved only by kiln-drying of the kind described in Chapter 6.
A further criterion that must be taken into account when using coconut palm wood is its limited resistance to weathering. It is usable to only a limited extent for products in the outdoor area. In addition to design (structural) protection of the wood, chemical wood protection is indispensable when using palm wood out of doors.
The possibilities for using coconut palm wood will be demonstrated below with the aid of photographs from various areas of use.
Coconut wood has been successfully used to build houses of different standards (low-cost - Photos 2, 3 - as well as executive-type), for industrial and office construction as well as buildings for recreation (Photo 4) and worship (chapel) in Zamboanga and Davao, Philippines (Photo 5). In executive houses (Photo 6), e.g., all structural parts are made out of coconut wood. Where exposed to weathering, they have been treated before construction. The coconut wood framework is, on the inside, covered with tongued and grooved (t & g) coconut wood boards, the outside is covered with pressure-treated coconut wood panelling (Photo 7). Stairs and floors as well as door-and window frames (Photo 8) are made of high density coconut wood. The porches are ornamented with turned coconut wood balusters (Photo 9). Attractive furniture and accessories for offices, living-rooms and classrooms have been manufactured (Photos 10, 11,12,13, 14,15,16, 17). Tool handles of coconut wood are in use (Photo 18), as well as fence posts (Photo 19), house posts, transmission poles (Photos 20, 21) and crates (Photo 22).
- face veneer for plywood (coconut veneer sheets disintegrate during drying).
Technically feasible but uneconomical:
- manufacture of pulp and paper
- manufacture of chipboard and fibreboard (recovery too low due to high percentages of fines and high consumption of glue/resin).
Photo 2: Low-cost house
Photo 3: Handplaning of coconut beam for low-cost house construction
Photo 4: Coconut pavilion roofed with coconut shingles
Photo 5: Roof construction of coconut chapel in Davao, Philippines
Photo 6: Bungalow with coconut wood - the pillars are hollow cylinders
Photo 7: Detail of wall with bricks made of coconut sawdust and wall-panelling
Photo 8: Details of coconut wood house (window frames)
Photo 9: Turned balusters
Photo 10: Chair
Photo 11: Laminated table-top
Photo 12: Briefcase
Photo 13: Dining-room table and chairs (Pacific Green, Fiji)
Photo 14: Coconut wood - upholstered furniture (Pacific Green, Fiji)
Photo 15: Living-room furniture and accessories (Pacific Green, Fiji)
Photo 16: Coconut palm wood furniture exhibited at International Furniture
Fair in Cologne, 1994
Photo 17: Coconut palm wood furniture exhibited at International Furniture
Fair in Cologne, 1994
Photo 18: Tool handles
Photo 19: CCA-treated fence post
Photo 20: CCA-treated power pole
Photo 21: Fungal attack on untreated power pole
Photo 22: Crates
The machining of coconut palm wood is rendered difficult by the structure of the wood. For cost reasons these difficulties must aIready be taken into account during design (see also Table 4), otherwise processing may become uneconomic and the products do not have the required qualities. The effects of the properties of the wood on its processing during the machining operation are listed in Chapter 8.
Table 4: Design guidelines for industrially manufactured products
|Problemetic:||To be Preferred|
|Designs and jointing techniques that require a large proportion of manual work||Designs and jointing techniques that can be carried out by the use of machinery|
|Mortise and tenon joints||Dowelled joints, if strength is sufficient|
|Profiles with a large material removal volume/large profile depth||Profiles with a small material removal volume/small profile depth|
|Dovetail joints/Finger joints||Dowelled joints|
|Frames with a counter profile||Frames with mitre joint|
|Edge radius < 5 mm||Edge radius > 5 mm|
|Highly profiled lathe-turned components with a profile base narrowing to a point||Lathe-turned components with small profile projections and a profile base narrowing to a rounded shape (circular rods, hollow cylinders)|
|Absolutely to be avoided:|
|Highly profiled cross-grain wood||Non profiled cross-grain wood with rounded edges|
|Finger joints||Longitudinal wood joints with dowels or tongue|
The fact that the strength properties of coconut wood are lower compared to other wood species of the same density classes must be taken into account in the design and jointing techniques for a product. This is especially true for all wood joints in which there are glue bonds between the connecting longitudinal and transverse wood surfaces. The dowel led joint, which has distinct advantages in its manufacture, is especially critical here unless adequate precautions are taken to avoid the known negative factors. Even with coconut wood, however, the dowelled joint can achieve the strengths required in the construction of furniture, windows and doors provided that appropriate precautions are taken.
With regard to strength properties, the mortise and tenon joint, especially the double mortise and tenon, is superior to the dowelled joint. The reasons for this are the large glued areas and the fact that it involves mainly an adhesive bond between the longitudinal surfaces of the wood. However, the mortise and tenon
joint has significant manufacturing technology disadvantages compared to the dowelled joint (in this connection see Chapters 8.6.6 and 8.6.8).
The dowelled joint is a simple and universally usable joint. It is used as a frame corner and box corner joint. When using coconut wood, adequate strength values are achieved if the glue is adjusted to a high viscosity and/or the glue is applied several times, especially in the cross-grain wood region, so that excessive absorption of the glue does not occur (starved glue line). This also applies to dowel holes, which have a high proportion of cross-grain wood, depending on the position of the drilled hole. In addition, in the case of jointing surfaces in the cross-grain wood region, special care must be taken to ensure that there are no raised vascular bundles that prevent an accurate, tight joint fit. Figures 5,6 and 7 show the principle of dowelled joints. The dowel spacing distances should not exceed 120 mm.
Fig. 5: Principle of a dowelled joint
Fig. 6: Butt-dowelled frame corner
Longitudinally profiled components are particularly suitable for mitred corner joints.
Source: Nutsch, 1983
Fig. 7: Dowelled mitred frame corner
Source: Nutsch, 1983
Tongue and groove joint
The tongue and groove (t & g) joint is simple to machine. An inserted tongue (extraneous tongue, lamello) should be used in the construction of tongue and groove joints in coconut wood to avoid pronounced splintering. The same points as in the case of the dowelled joint apply in regard to glue adjustment and application rate and the joint fit (raised vascular bundles). Figures 8 and 9 show the principles of tongue and groove joints.
Fig. 8: Principle of a tongue and groove joint
Fig. 9: Tongue and groove joint with inserted tongue
Source: Nutsch, 1983
It is possible to design furniture of panel construction with coconut palm wood by means of solid wooden panels (glue-laminate wood panels). The panels are manufactured by gluing wood strips together in the width (see Figure 10). Gluing the strips in the length using finger joints is a problem with coconut palm wood (see Section 8.6.9). The dowelled or tongue and groove joint in the cross-grain wood region is recommended as a jointing principle for longitudinal joints. Strict adherence to the density class is necessary when selecting the wood. Otherwise the panels warp or dissimilar shrinkage and swelling effects occur between the bonded wooden strips. In addition to using the same density class in a single glue-bonded component (panel, squared timber, beam), attention should be paid to uniformity of colour among the individual elements (strips) that are to be glued together. It is also advisable to pay attention to the number of vascular bundles in a surface unit, since these affect the optical and strength characteristics (see also the following section 2.2.2).
Laminated beams of the kind used to achieve load-bearing building structures and rather large spans or structural component lengths can be manufactured using coconut palm wood (see Photos 23 – 26). Because of their poor weathering resistance, they are usable only in a protected environment (in this connection see Chapter 7).
Fig. 10: Glue-bonded profile for full-width bonding
Photo 23: Laminated and bolted coconut boards
Photo 24: Laminated roof trusses joined by a nail plate
Photo 25: I-beam with plywood webbing
Photo 26: Laminated and bolted roof construction
A further design alternative is offered by sections of coconut palm trunks lathe-turned circular on the outside and centre-bored to an internal diameter of approx. 170 mm. These hollow cylinders (tubes) can be used structurally and decoratively, either as a whole or divided lengthways. Examples of their use include: cheeks and side-pieces for shelves or wall units, side-pieces for the supports of chairs and tables, posts, beams or trusses for wooden structures of all kinds (see also Photos 6,14, 15, 16). As a result of this tube principle, high strengths can be achieved, far exceeding the strengths of the massive material (the trunk as a solid cylinder). Another advantage is that drying cracks are prevented, which occur when drying material with different density areas.
In addition to its colour, the texture of coconut palm wood is also a conspicuous feature (see Figure 11). The intensity of the vascular bundles stands out to an extent that varies depending on the position in the trunk. They decrease towards the centre of the trunk and towards the top. In a longitudinal section the vascular bundles are as a rule seen as lines running more or less parallel. In a cross-section they appear as dark points in the light-coloured parenchyma tissue. In a diagonal section they appear as short, thick lines. Depending on the arrangement of the different graphical forms of the vascular bundles in the product, an aesthetic image is formed that contrasts with the inherent simplicity of the coconut palm wood.
Fig. 11: Vascular bundles in longitudinal, transverse and diagonal section
Source: Rossmann, 1994