Coconut wood is classified as non-durable. In order to prevent any attack of fungi, mould or insects during drying, a dip treatment previous to stacking is necessary. Timber used in the interior, e.g. for wall-panelling or furniture, should only be treated if it is of low density. In this case a boron treatment against insects is advisable. All timber exposed to weathering conditions as well as timber in ground contact needs an additional long term treatment after seasoning and machining.
In construction and housing, ground contact of timber should be avoided in order to prevent the transfer of moisture or insects from the soil. Equally, direct contact with concrete foundations should be avoided. It is advisable to place a layer of tar-paper between the foundation (bricks, concrete foundation, pillars) and the coconut wood. If on pillars, additional protection against termites can be provided by placing “termite shields” between the wood and the pillar. These are thin pieces of galvanized sheet metal bent at an angle of about 45° downwards (Figure 44).
Fig. 44: Termite shield
Ground
Water pockets create an ideal environment for fungi to develop. The possibility of water pockets developing should therefore be eliminated, especially at window sills, which should have a protruding “dripping edge”. No low density timber should be taken for exterior use. For fence posts, which are usually quartered or split, the low density inner part should be carved out with an axe (Figure 45), All round poles should be cut off at an angle on top to facilitate water run-off. The top then has to be sealed or covered by sheet metal to protect the fastest decaying low density pith of the pole.
Fig. 45: Manufacture of coconut fence posts
Source: PCA, 1977
Wood preservatives are chemical compounds used to protect timber against fungi and insects. Dependent on the solvent, we distinguish:
- oil-borne
- water-borne and
- organic solvent-borne preservatives.
The preservatives most commonly applied are (Willeitner and Liese, 1992):
- Creosote
- NAPCP
- CCA
- CCB/CCF
- CC
- AAC
- CU-HDO
- Methylen-bis-Thiocyanate
- Boron
- Borax
- Captafol/Chlorothalanil/Timbafol.
Creosote(coaltar) is an oil-borne derivative of coal, which in the past has been widely applied for preventive treatment of timbers in ground contact or exposed to weather conditions. It protects the timber both against fungal and insect attacks. Creosote gives the timber a blackish colour and exudes a pungent smell, which makes it unwanted for inside use.
NAPCP(Sodium-penta-chloro-phenate) is a water-borne preservative used to prevent fungal growth. It may have side-effects on humans and is therefore banned in a number of countries. Although it is an excellent fungicide, its use is discouraged due to its potential toxicity for man.
CCA(Chromium-Copper-Arsenate) is also water-borne and exists in various formulations with different kinds of chemicals. CCA has been widely and successfully used in the tropics, since it gives an effective and longlasting protection against a wide range of wood destroying organisms including termites. In ground contact the protection is limited, however (Willeitner and Liese, 1992). The retention required is 5 – 12 kg/m3.
CCB/CCF(Chromium-Copper-Boron and Chromium-Copper-Fluorine) are water-borne preservatives in which the arsenic has been replaced by Boron or Fluorine. These salts show less intense fixation and are less effective than CCA (Willeitner and Liese, 1992). The retention required is 5 – 15 kg/m3.
CC(Chromium-Copper) salts are highly effective against soft-rot, but less against brown - and white rot fungi, and insects. The retention required is 10 – 20 kg/m3.
AAC(Alcyl-Ammonium Components), also called Quaternary Ammonium Com pounds a re organic water-borne preservatives which give only little protection to timber in ground contact. They show hardly any penetration if applied without pressure. The retention required is 5 – 10 kg/m3.
CU-HDO is an expensive new Organic Copper Compound giving good protection against fungi and insects, also in ground contact. No experience exists so far for termites, however (Willeitner and Liese, 1992). The recommended retention is 4 – 20 kg/m3.
Methylen-bis-Thiocyanate (MBT) is a substance effective mainly against blue stain fungi and moulds. It is available as a 5 % solution and should be further dissolved to 1 – 2 % for use. MBT has a very low toxicity for humans and animals.
Boron is an element giving good protection against some insects, and to a limited extent, against fungi. It is usually applied as salt (Boric Acid, Borax) and applied in the diffusion process.
Captafol/Chlorothalanil/Timbafol are water-borne agricultural fungicides.
The preservative successfully used for dip-treatment is a 5% aqueous solution of sodium pentachlorophenate (NAPCP) and 2 % Borax during rainy season or 2.5 % NAPCP and 2 % Borax during dry season. However, due to its high toxicity, it is banned in various countries. Of various alternatives tested a 1% solution based on the active ingredient Methylen-bis-Thiocyanate has proved most successful. Another preservative, although less longlasting in its efficacy, is a Captafol/Chlorothalanil mixture which has a low toxicity rating for humans. It is available as a compound in powder form (e.g. Timbafol C) and is applied as 4 % aqueous solution. For timber in ground contact, especially power poles and fence posts, creosote can be used. However, it can not be painted over, smells strongly, and on the whole is in many countries more expensive than waterborne preservatives.
Exposed timber should be pressure-treated, preferably with water-borne preservatives. These are usually available in powder form (salt) and are dissolved in water. The most commonly used salt-type preservative in the tropics is copper-chrome-arsenate (CCA), which is very efficient against termites. Some brands are Tanalith C, Boliden K33, and Celcure AP. Other toxic salts are copper-chromium-boron and copper-chromium fluorine. CCA is not advised for roof shingles, where the roof is used as catchment for drinking water.
Timber scheduled for treatment should be free of defects. All machining, i.e. borings, recesses etc. have to be carried out before preservation. The timber has to be seasoned in order to achieve adequate penetration of the preservative and its uniform distribution.
The simplest method applied, which does not require any preservative is the charring of timber. However, it only provides termporary protection.lt is particularly applied for cheaper timber in ground contact, e.g. fence posts (Figure 46, 4 – 7).
Fig. 46: Charring of pole
Source: PCA, 1977
Fig. 47: Charring of larger number of poles
Source: PCA, 1977
In order to protect the timber during seasoning, the boards have to be dipped in a preservative solution immediately after sawing (Photo 42). The dipping tank can be welded out of half-cut oil drums, or out of a wooden box lined with plastic sheets. The tank should be placed between the resaw and the seasoning sheds to allow an unimpeded workflow. The boards should be free of sawdust and remain in the preservative for at least a minute before being removed and stacked. The solution has to be exchanged at intervals to sustain its toxicity.
Photo 42: Dip treatment of coconut boards
The minimum solution strength of the preservative applied by this method is 3%. Depending on the moisture content of the timber and the roughness of its surface, 1 to 3 coatings have to be applied. However, this method has limited effect only.
The timber to be treated can be soaked in a 3 – 5 % solution for up to 8 hours (depending on use and thickness). Soaking provides better protection than brushing or spraying (Figures 48, 49).
Fig. 48: Vessel for soaking
Fig. 49: Soaking of poles in hot preservative
Source: PCA, 1977
Two open tubs of appropriate length and volume are required to accommodate the timber sizes to be treated. They should be made of stainless steel in order to withstand the corrosive effects of the preservative. One of the tubs should be equipped with a heating source (Figure 50, Photo 43).The timber is submerged in the preservative (e.g. pentachlorophenol in heavy petroleum, or creosote) and heated for 2 – 3 hours up to 100° C. Then the timber is transferred to the other tub filled with the same preservative but cold. Here it is again kept for 8 – 24 hours. In both tubs the timber should be totally immersed. During the hot bath, air in the wood expands and is forced out. During the cold bath, the residual air in the wood contracts, thus creating a partial vacuum which allows the preservative to penetrate. Brion (1984) suggests another hot and cold bath treatment, where the hot bath contains boiling water and the cold bath a 3 – 4 % CCA solution (Table 19).
In both cases the timber has to be stacked after treatment under shade with stickers in between for at least 48 hours before use.
Fig. 50: Hot and cold bath for impregnation of power poles
Source: PCA, 1977
Photo 43: Hot and cold bath
Table 19: Soaking time for hot and cold bath (water/CCA)
| Board thickness mm | Soaking time (hours) | |
| Hot bath | Cold bath | |
| 12 | 1 | 8 – 12 |
| 25 | 2 | max. 12 |
| 50 | to be determined during process | 18 |
| thicker | 24 | |
Sap displacement method
The simple sap displacement method using caps (Boucherie method) has not proved to be successful with coconut wood. However, patchy to complete penetration was achieved when injecting 10 % CCA solution into the logs at a pressure of 800 kPa (Palomar, 1979).
Simple diffusion process
The sawn timber is dipped into a 20% solution of boron heated up to a temperature of 40° C. The immersion time should last at least 20 minutes After dipping, the timber is stacked closely and covered with polyethylene sheets in order to avoid evaporation of moisture during storage. The storage time, during which diffusion occurs, shouId take at least six but preferably 10 weeks. After this period an overall retention of boron of about 3 % of the oven-dry wood weight can be achieved (Palomar, 1986). After diffusion, the treated timber can be used for most purposes in construction. However, it should not be exposed to weathering or used in ground contact in order to avoid hazardous leaching. This method is simple but time consuming.
Double diffusion process
The double diffusion process has given good retention values and is recommended particularly for power poles. It can be applied to green timber, which reduces the processing time as well as the danger of fungal or insect attack during seasoning. However, the poles have to be debarked to allow proper diffusion to take place. The timber is immersed into a hot (80° C) copper sulphate solution for 3 – 6 hours (depending on thickness) and cooled overnight (FAO, 1985). The next day the timber is transferred to a tank containing a cold solution of sodium dichromate and arsenic pentoxide, where the timber is kept for up to two days. Afterwards it is stacked for seasoning in a suitable place (Figure 51).
Fig. 51: Debarked poles stacked for drying
Source: PCA, 1977
The application of pressure to force preservative into the wood in a pressurized cylinder is still the most efficient way of treating timber and obtaining good absorption values. It is done in a commercially supplied pressure plant equipped with pressure cylinder, gauges, storage tank, vacuum and pressure pumps (Photo 44). Various processes have been developed. The most common are the full-cell-process (Bethell), and the empty-cell-process (Rueping). For pressure treatment, the coconut wood has to have a maximum moisture content of 30% (according to Sulc, 1983, the fibre saturation point for coconut wood lies at 24 %).
The following (full-cell-process) schedule has been successfully applied for coconut wood in Zamboanga (Table 20):
Table 20: Preservation schedule
| Use | Material | Size mm | Solution %CCA | lnitial vacuum-85 kPa | Pressure vacuum 1400 kPa | Final vacuum-85 kPa | Minimum absorption l/m3 |
| (min) | (min) | (min) | |||||
| exposed | sawn | 25 | 2 | 20 | 45 | 10 | 250 |
| exposed | sawn | 50 | 2 | 20 | 60 | 10 | 250 |
| ground contact | round | 6 | 30 | 120 | 10 | 200 |
Source: FAO, 1985
| Remark: | exposed: | • | to weather, not in ground contact |
| absorption: | • | depends on density, e.g. minimum of 250 litres/m3 for high density timber | |
| % CCA: | • | for structural or high value components, 3 – 4 % recommended. |
However, it has to be borne in mind that the initial as well as the maintenance costs for such a pressure plant are substantial. For operations on a smaller scale, the hot and cold bath method is therefore recommended.
| Caution!! Most preservatives are toxic |
|
Photo 44: Pressure plant
