TIMBER SEASONING

Seasoning is the reduction of moisture content of timber to that of the-surrounding air - Sydney area approx. 12.3%.Timber is seasoned to dry out the timber to bring it to a usable and workable condition. More than half the weight of freshly cut timber consists of moisture or sap. Before the timber can be used a large part of the moisture must be removed.

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Reasons for Seasoning

Air - natural circulation of air around & through timber stacks. --- Time - 3-9 months, sometimes years. - Kiln - forced drying of timber stacks in large containers called kilns - Time 1-3 weeks. - Combination of Air & Kiln - combines advantages of both air and kiln. - Solar kilns – rely on solar energy to aid the drying process - Time 1-3 weeks For more information on seasoning of timber go to Drying timber in Australia.Seasoned timber has many advantages over unseasoned timber, such as: improved strength and hardness

To prevent shrinkage, splitting, checking and warping.
To achieve greater stiffness and strength.
To allow penetration of preservatives
To obtain a surface that will accept paint, polish or glue.
To protect against decay.

Methods of Seasoning

Air Seasoning
The timber is stacked on foundations to keep it off the ground. Strips of wood (about 38 x 19 mm) are placed between the layers of boards to allow air to circulate. Ends of boards may be painted to retard drying and prevent splitting. A waterproof covering is placed over the stack to protect the timber from the sun and the weather. Air seasoning is slow, taking up to a year for a piece 25 mm thick and considerably longer for thicker pieces. But the timber produced is well suited to outdoor work.

Kiln Seasoning

Kiln seasoning is done in a large oven-like structure in which air circulation, humidity and temperatures are controlled. The timber is stacked on the trucks in the same way as for air drying. The trucks are on rails so that they can be moved into the kiln. Care must be taken to see that the drying process while removing the free water is not too rapid, as at this stage the timber is susceptible to degrade (damage) by checking and collapse. Many types of softwood, such as Radiata Pine, can be kiln dried easily and fairly cheaply from the green condition. But many of the Australian hardwoods are so slow in drying that their kiln drying is uneconomical. It is, however, satisfactory and economic to season them by the combined process of air and kiln drying mentioned below.

Seasoning defect

Defects in Timber

Quality drying of lumber depends on numerous factors. This section describes some of the simpler aspects of stacking that can be more readily implemented and will yield immediate results. .

Sticker Thickness

A common sticker thickness is 3/4 inch. The typical thickness for stickers in industry can vary from 5/8 inch to 1 inch thick. It is unfortunate, however, that some individual kilns will have even more variation. While variation in sticker thickness at an operation isn’t a problem by itself, it becomes a problem when the stickers of various thickness appear in the same lumber course or same kiln charge. The easiest way to avoid this problem is to have only one sticker thickness and as near to 3/4 inch thick as possible. By keeping only one sticker thickness, it is impossible for stickers of various thickness to get mixed. Sticker thickness is important because uniformly thick stickers will block airflow during drying and result in warp and nonuniform drying. Thick stickers can be resurfaced to the target thickness, and thin stickers are best used at the next hot dog and marshmallow roast, if there is no wood-fired boiler.

Sticker Straightness

Crook and kink in stickers can often cause problems in sticker feeding automatic stackers and also in sticker alignment in semiautomatic or hand stacking. Discard stickers with more than 3 inches of crook or kink or 3 inches shorter than the width of the stack.

Bolster Thickness

Another common source of problems when stacking lumber are the bolsters used between lumber stacks. As was the case with sticker thickness, the chances also increase for the lumber to warp if bolsters are of uneven thickness. The uneven thickness of the bolsters can block airflow in adjacent lumber stacks in a kiln. Some kilns that have experienced airflow blockage have solved the problem by using bolsters that are the same thickness in both directions. It is important that the bolsters be nearly the same length of the lumber stack, but a problem arises when the rectangular bolsters are of uneven dimension in the other two directions. Therefore, if a bolster is turned the wrong way, this will have a similar effect as thick and thin bolsters.

Sticker Placement

Stickers serve two main purposes. First, they separate the courses of lumber so air can move through to dry the lumber. Second, they distribute the weight of the lumber vertically from top to bottom—through the stickers and bolsters down to the kiln truck or load supports. Stickers out of alignment, on edge or missing can be costly to lumber quality by causing kink, twist, skitipped ends and other forms of warp. Sticker alignment is seldom perfect, especially with manual sticker placement. The ideal is to have all stickers vertically aligned in a column. The stickers should at least be placed so they overlap the ones above and below. If a sticker is missing, the courses above the space will sag down into the open space. The weight of the wood above bearing down on the unsupported board will place a very large bending force on the board, causing it and several boards above to warp. Stickers placed on edge will have the same effect as thick stickers. The board above will tend to warp or, in softer species, the sticker may actually indent the board above and below the turned sticker. If a sticker is missing, the courses above the space will sag down into the open space. The weight of the wood above bearing down on the unsupported board will place a very large bending force on the board, causing it and several boards above to warp. Stickers placed on edge will have the same effect as thick stickers. The board above will tend to warp or, in softer species, the sticker may actually indent the board above and below the turned sticker. Stickers should be within one sticker width of the end of the stack. One primary purpose of the stickers is to hold the boards flat. If either end sticker is significantly removed from the pile end, there will be no support on the lumber ends. This can lead to warp, twist, cup and splitting of the unsupported ends. It is commonly stated that an end split will extend up to the first point of good sticker contact.

Board Placement in Packages

Providing adequate sticker contact and board control at the ends of a package is critical to good drying as discussed. Even ends on all packages are needed to provide optimum sticker placement and sticker contact on board ends. Most hardwood lumber is manufactured and sold random length, and many mills do not double-end trim. A method of stacking called “box piling” can provide even-end packages. Unfortunately, stacking machines do not box pile. Instead, most even end at one end of the stack, letting the other end take up all the uneven lengths. The maximum length lumber to be stacked will determine the pile length. Full-length boards are selected for the edges of each course. Boards in between are alternately pulled to each end. Consideration must be given to the best mix of package lengths relative to kiln size when the pile lengths are established. Failure to consider the kiln dimensions could lead to mixes of packages that will not fit in the kiln without leaving open areas.
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Seasoning defect photo

Timber stacking

Timber, before seasoning, should be stacked in yards free from weeds and debris.
The yard should have big shady trees to protect the timber from direct sun.
Ends of logs should be protected against splitting by applying anti-splitting
compositions and stacked on foundations in closed stacks in one or more layers.
Stacks should be protected against direct sun by providing a covering if needed.

Precautions to be Taken in Stacking Timber

Stacks of not more than 100 sleepers are recommended to be made

Poles are stacked either in closed heaps or with crossers. If stacked in closed heaps, then there should be alternate layers of butt ends and of top ends so that the two ends of the stack are level. Poles themselves could be used as crossers, which should not be spaced more than three metres.

Fence posts should be stacked in open crib fashion in which successive layers of posts are at right angles to each other and there is a gap of about 8 cm between adjacent posts in the same layer. Centre to centre distance between crossers should not exceed 1.5 m and the height of stack should not exceed 3 metres.

Horizontal stacking of sawn timber is done on vertical pillars of treated timber, brick masonry or of cement concrete 30 cm square in section and 30 to 45 cm high. The pillars are spaced 1.2 m centre to centre along the length and the breadth of the stack. The length of material to be stacked decides the length of stacking unit. Long beams of cross-section 10cm × 10cm and above are placed on the foundation pillars to form a framework for stacking timber.

Scantlings and squares should be stacked with crossers 5 cm × 4 cm in section and spaced 2.5 m to 3 m apart. The ends should be protected with moisture proof coatings.
Planks should be stacked on level platform with crossers of uniform thickness and section, which should be in vertical alignment in a stack. Longer planks should form the bottom of the stack and the shorter one’s the top. Heavy wooden beams should be placed on the top to prevent top layers from warping. A gap of about 2.5 cm should be left between adjoining planks for free circulation of air in the centre of stack. The stack should be protected against rain and sun by providing a shed over it.

Type of stacking

HORIZONTAL STACKING

Most Common Method of stacking Suitable for All Forms Of Sawn Timber From small Veneers To Big Poles It vary with species , thickness of sawn material And climatic condition of the locality.

VERTICAL STACKING

Mainly used in rapid surface drying of non refractory wood The two precaution should be taken in vertical stacking @ the planks stacked for seasoning should be turned frequently at least twice a day expose both the sides to the sun otherwise warping may occur @ the lower of the planks should rest on some waste to prevent the fungal and insect attack and also prevent it from direct contact with the earth after partial drying better to stack in horizontal manner.

CLOSE CRIB METHOD

In this method, reduced air circulation slows down the pace of seasoning. This method is recommended for staking heavy structured timbers like sal in hot and dry localities.

OPEN CRIB METHOD

This method is a modification of the close crib method and because of more air circulation taking place it is more akin to the one and nine method in its effects.

ONE IN NINE METHOD

This method of stacking timbers is best suited for moderately heavy coniferous timbers in hot climate and for heavy timbers in moist climates.

PRESERVATION OF TIMBER

Timber has to be protected from the attack of insects, e.g. white ants etc., and from internal decay due to dry and wet rots.

Perfect seasoning is the most effective means of preservation. Timber should be

so used that either it is wholly dry and well ventilated or is wholly under water. It will not decay when kept under water but it will become soft and weak.

Proper damp proofing of the building and providing free circulation of air around the built in portions of timber are essential for the preservation of the timber used. However, when these conditions cannot be obtained then preservatives have to be applied for preservation.

Timber should be well seasoned before the application of preservatives as otherwise the preservatives would block the pores of timber thereby causing its decay due to the entrapped moisture.

Direct contact with lime mortar should be avoided while using preservative with masonry.

Methods of Preservation of Timber

Following are some of the common methods of preservation adopted

(i) Charring

(ii) Tarring

(iii) Painting

(iv) Creosoting

(v) Wolman salt

(vi) Ascu treatment

(vii) Fire proofing of timber

Charring

Lower ends of the posts that are to be embedded in ground are generally charred with a view to prevent dry rot and attack of worms. It is done by quenching the ends of posts in water after they are charred on wood fire to a depth of 1.5 cm.

Tarring

It consists in coating with tar or tar mixed with pitch. Embedded portions of timber fence posts, ends of door and window frames, battens and beams built in wall are usually tarred. Tarring is not done in case of those portions of structural members that are open to view, because of unsightly black colour.

Painting

A paint when applied to timber acts not only as a good preservative but also it enhances the appearance of the surface so treated. Only well seasoned timber should be painted as otherwise the moisture entrapped in the timber, because of the closing of timber bores by paint, would cause decay. Paints however, protect seasoned timber against moisture thereby prolonging its