Drying increases the strength of timber, its durability against fungal attack and makes it more stable. The objective of drying timber is to achieve a uniform moisture content, minimising seasoning degrade (splitting, ceil collapse, insect damage, staining etc), in minimum time. The required moisture content is usually the same as in the environment where the timber is to be used, to keep the finished articles stable in use. 

Drying costs about $200/m3 and adds more than this to the value of the wood. 

Rob Rule took us into his "deep theory land" for about half a day to teach us about the material of wood and its cells, where water is stored in wood and where timber's strength comes from (long wood fibres filled with minerals, increasing its density). He reckoned if we understand the reasons for doing things, we should be able to avoid mistakes (cell collapse, drying defects) and learn what to do better next time if we do dry wood too quickly. 

Free water is stored inside cells and water vapour is stored between cells. Once the free water is removed, the wood is at Fibre Saturation Point (FSP), typically 25% moisture content. If the free water in hardwood dries out too quickly, checks (small cracks and voids), splits and large cracks can occur, degrading the timber. At moisture contents drier than the FSP, we are removing bound water stored in cell walls. Drying down to 15% for structural timber or 12% for furniture and cabinet making timber takes time to remove the more tightly bound water. The time to reach equilibrium moisture content in passive air drying is usually 1 year per 25 mm of timber thickness To achieve 8% or-6% moisture content required for a very dry, inland or mountain environment such as the continental USA, requires energy (heat) as well. We were given information on suppliers of solar and other kilns to find out more. 

I learnt some practical things from understanding the growth and structure of wood. For example, there is no point saving branches for structural use. The bending stresses built into the wood when it grows result in "reaction wood", that changes shape when sawn. 

We learnt about stacking sawn timber to dry it. Barry Moon used his Lucas Mill to saw a big green ironbark log into boards in 20 minutes. We "block stacked" the wet boards solidly, as close together as possible. We wrapped them in coloured plastic (for six to eight weeks) to slow down the initial drying, in order to avoid surface checking. Backsawn red stringybark will surface check (small cracks visible on the surface, spoiling the wood's appearance and lowering its strength) in 20 minutes to half an hour on a hot. windy summer's day, If you have a choice, cut easy-to-dry softwood in summer. 

To avoid seasoning degrade, dry the timber in the slowest recommended way. This will however delay the return on your investment. but it does reduce the need to think and makes up for lack of experience. A 15% loss means you are doing well. Once you get very good at it (if you have a forest to practice on). you can reduce waste to 6%. It occurred to me that one of the reasons it is so hard to get large sections of Australian hardwood now is the drying difficulty. Acacia melanoxylon (blackwood) is available in 100 by 100 mm sections because it is easy and fast drying. Most of the eucalyptus species are intermediate. slow or very slow drying. as are arid zone casuarinas (sheoaks). 

When we stacked the Whitaker's cypress to air dry it, I was bowled over_ by the abandon with which lovely 100 mm by 100 mm cypress was cut into 1.2 m lengths for bearers at 900 mm centres to support the stack. We had to cut a lot of wood into 50 mm wide by 35 mm high strip sticks (at 450 to 600 mm maximum spacing) to go between each layer. We learnt that it is best to remove the bark when green ~and freshly cut (to reduce insect attack as they lay their eggs under the bark). 

It might be hard for a romantic timber. lover to remove substandard timber before drying, to save effort later. It seems that some timber is firewood grade and will become a greenhouse gas quickly. It helps to knowhow to maximise quality and yield. 

Instead of burning what might have become firewood, we can now turn trees on our farms into high quality Australian hardwoods. If we make furniture or a house, we might make it of a quality our descendants could keep as an antique in the future. 

Owen Whitaker gave a short talk about the benefits of biodiversity and multi purpose, multi species plantations. More species leads to more insect predator habitats, reducing damage ecause insect attack is usually then less intense. Mixing in wattles adds to the understorey and kick starts biodiversity. This leads to a more stable system than a monoculture of whatever we or the Forestry Commission thinks might give the best return 27 years into the future. 

DAVlD EDEN