Timber
| Infobox on Timber | |
|---|---|
| Example of Timber |  |
| Facts | |
| Origin | This table shows only a selection of the most important countries of origin and should not be thought of as exhaustive.
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| Stowage factor (in m3/t) | See text |
| Humidity / moisture |
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| Ventilation | If the product is dry for shipment, ventilation is not normally required. However, if there is a risk of drying or moisture damage, ventilation should be provided. The following ventilation measure is then recommended: air exchange rate: 6 changes/hour (airing) |
| Risk factors | Mechanical damage(s) may occur (see text). |
Timber
Contents
Description
Lumber (also known as Timber) is supplied either rough or finished. Besides pulpwood, rough lumber is the raw material for furniture-making and other items requiring additional cutting and shaping. It is available in many species, usually hardwoods. Finished lumber is supplied in standard sizes, mostly for the construction industry, primarily softwood from coniferous species including pine, fir and spruce (collectively known as Spruce-pine-fir), cedar, and hemlock, but also some hardwood, for high-grade flooring.
Commercial timbers fall into two main categories, softwoods and hardwoods. The distinction is botanical and does not indicate hardness, e.g. Balsa is a hardwood. As a generalization, softwoods are coniferous (evergreen) and hardwoods are deciduous (broad leafed). There are exceptions. After conversion by sawing to useable sized, it is necessary to remove the inherent moisture (seasoning). This makes the timber more stable, resistant to decay and insect attack, lighter, stronger and easier to work and finish.
Moisture content over approximately 21% and lack of ventilation can lead to mould and fungal growth, which can result in permanent staining and decay. Drying timber is effected by stacking and separation of the tiers of pieces with dry square sticks to allow ventilation by ambient air or heated air in a kiln. Timber which has become wetted in transit should be dried by similar methods. Shrinkage, twisting, splitting, etc. take place as drying below approx. 21% moisture content occurs, and this operation may result in a proportion of degrade. Care should be taken to ensure that what is claimed to be wetting in transit is not confused with excess inherent moisture, due to insufficient seasoning. This may be determined by the extent to which the whole parcel has high moisture content and the degree to which discolouration has occurred in comparison with what effect exposure to rain, etc., might have.
Wood is a hygroscopic material, which means it naturally absorbs and releases water to balance its internal moisture content with the surrounding environment. The moisture content of wood is measured by the weight of water as a percentage of the oven-dry weight of the wood fiber. The key to controlling decay is to control moisture. Once decay fungi are established, the minimum moisture content for decay to propagate is 22 to 24 percent, so building experts recommend 19 percent as the maximum safe moisture content for untreated wood in service. Water by itself does not harm the wood, but rather, wood with consistently high moisture content enables fungal organisms to grow.
Lumber may be divided into the following water content classes:
| Water content | Designation |
| 0% | Kiln dry lumber |
| 6 - 10% | Room dry lumber |
| 10 - 12% | Very dry lumber |
| 12 - 15% | Air dry lumber |
| 15 - 20% | Slightly dry lumber |
| 20 - 25% | Green lumber (forest dry) |
| 30 - 33% | Fiber saturated lumber |
| > 33% | Water saturated lumber |
Fiber saturation means that the cell walls (microsystem) are maximally filled with water, while water saturation means that all lumens (micro- and macrosystem) are maximally filled with water.
Boules
Logs sawn into thick planks, sticked, reformed and secured into their original round form (see Logs).
Logs
Hardwood logs are generally shipped in their round form, for conversion by sawing into timber or peeling/slicing into veneers in the country of destination. They can dry out, giving off moisture causing condensation and split at ends during this process. They may also be infested with wood boring insects.
Softwood logs are normally squared for use in large constructional sizes; these and pit props and scaffold poles, shipped in the round, may also contain high levels of inherent moisture.
Timber sheet materials
Chipboard/Flakeboard/Particleboard. Fragments of timber of graded sizes mixed with adhesive and pressed into boards of various standard trade dimensions. All are susceptible to breakage and wetting and claims may be disproportional due to high sorting and trimming costs and/or lack of residual values.
Hardboard/Medium Density Fibreboard (MDF). Boards made of macerated timber fibre, in other respects similar to chipboard.
Blockboard/Laminboard. Boards of standard timber trade dimensions, constructed from square timber core sticks, sandwiched and glued between outer sheets of veneer to produce a very stable board. The outer veneers may be of decorative quality. The glue is usually only moisture resistant (MR) and wetting may be very detrimental.
Plywood. Always constructed from an odd number of veneers, bonded together with adhesives, which may be water and boil proof (WBP) or moisture resistant (MR). Both glue lines are resistant to moisture, and whilst wetting should not detrimentally affect the construction of the boards, sanded or decorative finish of board surfaces will be significantly affected and result in substantial claims. Breakage/impact damage of edges will also result in claims.
Machined timber
Planed boards (PAR), mouldings, turned and many other items are now shipped internationally and many are as susceptible to the same damage as timber. Reconditioning may prove impossible because of their ‘finished article’ nature.
Veneers
Peeled. From round hardwood or softwood logs, usually for use in the manufacture of plywood.
Sliced. From quartered hardwood logs for decorative purposes. Usually packed in cases, crates or palletised. Breakage and staining are less of a problem with peeled veneers, which are normally produced oversize and trimmed after manufacture. Sliced veneers are detrimentally affected by staining/breakage and additional claims may be made due to loss of ‘run’ or ‘matching’. Moisture content is critical.
Softwood. If wetted should be stick-piled as soon as possible and allowed to dry out. Loss quite often is then limited to costs of sticking.
Softwood or Hardwood. Discolouration, provided this has not penetrated too deeply, can be planed out; this will result in a reduction in thickness but the timber remaining will be perfectly sound.
Sawn Softwood. Mould or fungus growth through the tissues of timber causes discolouration and incipient rot. Kiln drying should arrest this. Staining of a very dark character may indicate contact with water prior to shipment.
Boxboards. Usually originate from Romania or Portugal and are used for the construction of vegetable boxes, both retail and wholesale. Usually shipped on pallets with the boxboard bundled into individual units of 200 or 400 slats, and bound with wire.
Damage by water can cause mould to grow between closely packed slats. Damage by breakage usually occurs during stowage. Because of the low value, sorting and cleaning charges usually exceed the landed value of the units.
More information on softwood and hardwood timber
Part of the following report was produced by the Carefully to Carry Committee – the UK P&I Club’s advisory committee on cargo matters.
Softwood timber
The main areas from which softwood timber is shipped are the Baltic and North America. Very few claims arise from the Baltic or the East Coast of North America trades, but large claims have occurred on shipments or timber from the North West Coast of North America mainly due to the very wet climate in this area.
Softwood timber is commonly shipped in bundles or packages of planks of various lengths and sizes, secured with flat metal strapping bands. The timber is usually unprotected unless it has been kiln dried, when it is normally protected by a loose plastic wrapper.
Softwoods, and especially pine woods, carry a great deal of sap and are therefore very susceptible to fungal growth known as sap staining. This sap staining is of relevance only where strength or appearance is of prime importance. In this respect it should be borne in mind that clean timber is always a more attractive product. Blue staining occurs mainly in hardwoods and can be prevented by dipping the timber in chemicals. This must be don within one day of sawing the timber into planks or it may not be effective and may not prevent blue staining. The timber may also be stored in the open, exposed to inclement weather, so that water may destroy the effect of the chemicals. Fungus development is purely associated with the moisture content of the timber and therefore kiln dried timber that has been properly dried is normally not affected by fungal growth.
There is so much rain in the British Columbia area of the NorthWest Coast of North America that timber is often loaded during pouring rain and is wet before shipment in most instances. The problem is further exacerbated because the rain enters the ship’s hatchways and the tanktops can become partially flooded. Apart from the bottom packages of timber becoming thoroughly soaked, the water may stain the timber with rust marks picked up from the ship’s structure. It is therefore recommended that provision be made to keep the bilges pumped dry at all times when loading during rain. A further problem occurs in that the metal strapping bands securing the bundles of timber become rusty and the rust runs into the timber with resulting stain.
It is important to emphasize that many thousand of tons of softwood timber have been shipped over the years in a thoroughly wet condition on long voyages, with no ventilation between the planks or packages in the stow and with the timber remaining saturated for the entire voyage, without developing any defects as a result. Invariably, bills of lading are signed ‘clean’, as it is a well known fact that timber shipped from the British Colombia area is, in most instances, shipped in a wet condition. However, claims can arise as a result of blue staining, rust staining or, in some rare instances, rotting. Claims may also arise after discharge for drying the timber. It is therefore recommended that bills of lading should be claused with appropriate remarks to reflect the condition of the timber as shipped such as ‘timber stained with blue marks’, ‘strapping bands rusty’, ‘timber rust stained’, and ‘wet before shipment’.
Hardwood timber
Although hardwoods and semi-hardwoods are shipped from many tropical and semi-tropical countries in the world, much of this timber, especially from West Africa, is shipped as logs. Shipments of logs do not usually generate any cargo claims and therefore are not dealt with in this article.
Hardwoods and semi-hardwoods shipped from South East Asia, especially to Europe, are commonly shipped as planks in bundles or packages secured by metal bands. Most are unprotected. The following are some common types of timber from this part of the world.
Meranti is a relatively light semi-hardwood suitable for general construction, interior fittings and furniture. The sub-groups include, meranti bakau, dark red meranti, light red meranti, white meranti and yellow meranti. This timber is not durable under tropical conditions and is difficult to treat with preservatives. However, it is easy to work and seasons without trouble. It is shipped into Europe in large quantities and used extensively for doors, window frames and other outside uses.
Merbau is a heavy, hard, fairly strong and durable wood used mainly for heavy construction. It is bronze or red/brown in colour, weathering to dark red brown.
Ramin is a moderately hard, moderately heavy utility wood, easily treated with preservatives. It seasons quickly but is very liable to blue stain and it is therefore advisable to dip the timber in anti-stain chemicals after sawing. The timber is white in colourand usually free from quality defects. It is used extensively in the furniture trade and is highly susceptible to claims. There are of course many other species of timber but most shipments into Europe from S.E. Asia include some of the types above.
Applications
Lumber is wood in any of its stages felling to readiness for use as structural material for construction, or wood pulp for paper production.
Shipment / storage / usage
Loading and care of timber cargo
It is of paramount importance that cargo holds are thoroughly cleaned before timber cargo is loaded, of whatever type. Any grease and oil should be removed from the vessel’s structure, as contact can stain the timber. Remnants of previous cargoes should be removed from the overhead beams and the underside beams of hatch panels, as claims have arisen as a result of remnants of previous cargoes contaminating the timber. For example, iron ore dust when made wet by condensation can turn into a red liquid which can stain the timber; and ores or sand of an abrasive nature, such as ilmenite ore, can damage the saws in sawmills, if the timber has been contaminated. If the steel work of the hold is rusty, the timber should be kept clear of the rust by use of dunnage. Ship sweat developing during the voyage and dripping on the timber may also result in rust stains, therefore, correct ventilation and dunnaging is of great importance.
Bad stowage often results in the bands securing the bundles breaking. This is usually as a result of not keeping the stow level or crossing the bundles in stow, or a combination of the two. It is not unknown for the stevedores to work fork-lift trucks on top of the timber in the square of the hatch in bulk carriers, when the stow has reached about half the length of the hold. The surface of the timber in contact with the trucks usually becomes damaged by scuffing and through oil dripping from the trucks. If this method of loading is to be used, then steel plates should be carefully laid over the timber to protect it.
Care should always be taken during loading and discharge to use the correct equipment. Wire slings tend to score the lower corner planks in the bundles, especially when the slings are overloaded; therefore, rope or webbing slings are preferable. Fork-lift truck damage, caused by the forks of the truck being driven into the planks, is common. This results in deep score marks in the timber and, in many instances, splitting of the timber.
Careful supervision by the ship’s officers can prevent much of this type of damage.
Stowage factor
The stowage factor of the various species of wood is directly related to their density. A distinction is drawn between theoretical density and apparent density. Theoretical density is calculated purely on the basis of solid lumber, i.e. as if all cavities within a slab of lumber had been obliterated by compaction. Theoretical density is identical for all species of wood and is 1.50 g/cm3. Apparent density or bulk density is calculated from the weight and the volume of the lumber and differs from species to species in accordance with their differing structure. Comparisons can only be made between types of lumber with an identical water content. Fixed points are a water content of 0% (kiln dry lumber) and 15% (air dry lumber). Lumber is divided into the following categories by density:
| Very light species | < 0.40 cm3 |
| Moderately light species | 0.41 - 0.50 cm3 |
| Light species | 0.51 - 0.60 cm3 |
| Moderately heavy species | 0.61 - 0.70 cm3 |
| Heavy species | 0.71 - 0.80 cm3 |
| Very heavy species | > 0.80 cm3 |
Balsawood with a density of 0.14 - 0.44 g/cm3 is the lightest lumber, while quebracho (1.12 g/cm3), ebony (1.18 - 1.33 g/cm3) and guayac (1.20 - 1.30 g/cm3) are among the very heavy species. When suitable for such loading, cut lumber is also carried as deck cargo (up to approx. 50% of cargo volume or approx. one third of total cargo).
Seasoning of timber
Reduction of the moisture content of timber is achieved by either air drying or kiln drying. Timber is fully seasoned when the moisture content has dropped to the equilibrium moisture content of the local climate. This, in most cases, would be between 15% and 18%.
Air dried timber
As the name implies, air dried timber is timber that has been allowed to dry naturally, usually by stick piling the sawn planks in covered storage allowing natural air circulation between the planks. The time required for this process will depend on the type of timber and the climate. Once seasoned, the planks are secured in bundles with a number of flat metal strapping bands and are ready for shipment.
Often these bundles are stored in the open and exposed to the elements, resulting in moisture infiltrating the individual planks. Although this may result in the planks on the outside of the bundles having a higher moisture level than expected, these planks will quickly dry naturally. The condition of the internal parts of the bundles will depend on how long free moisture has been trapped within the bundles and also the nature of the timber, i.e. its resilience to the effects of wetness. In the worst situation, the planks will be mouldy, still wet and severely black stained.
In general, high moisture contents for air dried timber, without staining, do not provoke claims. However, if the moisture content is excessive, it is not unknown for receivers to claim the costs of stick piling to re-dry the timber. If such timber is not dried and remains in store, mould may develop and could lead to staining of the timber.
Air dried timber is often carried on deck with shippers’ approval, without protection. It is therefore obvious that wetness and high moisture content are of no real concern in shipments of this nature. In most cases, air dried timber has not been properly seasoned and has moisture contents well above the optimum levels which might be expected from the country of origin.
Kiln dried timber
Because seasoning takes a long time when timber is allowed to dry naturally, and because the process is therefore expensive in terms of storage costs, the technique of drying timber in ovens has been developed.
The timber, after treatment, is generally referred to as kiln dried timber. Sometimes, bundles of kiln dried timber are protected by plastic wrappers, and have a stencil on the outside of the bundle denoting the fact that the timber is kiln dried.
Kiln drying certificates usually specify to what degree the timber has been dried. The usual parameters are 8-12%, 14-16% or 16-18%. Provided the timber has spent sufficient time in the kiln and has been properly treated, the moisture content at the heart of each plank should show the correct degree of drying within one or two percent, even though the surface of the plank may show a higher level of moisture through natural absorption after the kiln drying process. Sometimes, the moisture content reading at the heart of the plank shows a higher reading than the outside of the plank and much higher than the drying certificate. This is a clear indication that the timber has not been properly dried. These points should be taken into consideration if receivers claim for redrying costs on wet timber. When granting allowances for redrying it should be recognized that stick piling for air drying may be all that is necessary if the outer surfaces of the planks only are affected. Stick piling is normally considerably cheaper than oven drying.
Claims for redrying of kiln dried timber represent a large proportion of claims on timber cargoes. It is often alleged by cargo interests that to stow kiln dried timber in the same cargo hold as air dried timber is tantamount to not caring properly for the cargo. Provided the air dried timber has not been exposed to rain before shipment and become saturated, any allegations of this nature should be rejected. Whether timber is air dried or kiln dried it will eventually adjust to the optimum moisture level compatible with its equilibrium relative humidity, developed in due course, through contact with the ambient air. Therefore, loading of air dried and kiln dried timber in the same ambient air will not effect the kiln dried timber to any noticeable degree during the voyage. Naturally, if dry timber is stowed in the same hold as saturated timber, the moisture content of the outer planks of the dry timber will increase through absorption.Experience has proven that in these circumstances the inner planks within the bundles are not affected during the course of a normal sea voyage. It is also true that wet timber, or timber with too high a moisture content, will not dry, irrespective of how well the bundles are ventilated in stow. On a normal sea voyage the timber will not deteriorate. However, if the timber is not dried when discharged, it will eventually decay.
If timber is kiln dried too quickly or the moisture level reduced too far, this can result in the timber cracking. Usually , any damage of this nature will not be seen at the time of shipment. Claims for this type of damage should be rejected.
Risk factors
- Mechanical influences
- Shrinkage/Shortage
- Insect infestation / Diseases
- Fungal attack