From the Forest to the Floor
We all connected to timber flooring everyday – whether it’s manufacturing, selling or installing, whether you sell timber, adhesive or finish – it all starts with a tree. We will trace the steps from the forest, sawmilling, drying, manufacturing through to the product being used on the floor.
INTO THE WOODS
History of forests in Australia
Australia has just over 147 million hectares of native forest and about 1.82 million hectares of plantations. With an estimated 4% of the global forest estate, Australia has the world’s sixth-largest forest area and the fourthlargest area of forest in nature conservation reserves.
Australia’s forests play an essential role in biodiversity conservation, the global carbon cycle, the supply of fresh water, and the maintenance of many cultural, social and environmental values. Forests also provide the resource base for economic activities that employ thousands of people across Australia, particularly in rural and regional areas.
The distribution of forests is broadly determined by climate and soil properties, although other factors such as fire regimes are also important. By far the most common forest in Australia is eucalypt forest, which comprises 78% of Australia’s total forest estate, followed by acacia, melaleuca, rainforest, casuarina, mangrove and callitris. Plantation forests comprise just over 1% of Australia’s forests and are mostly composed of eucalypts and nonnative pine species, especially radiata pine (Pinusradiata ).
16% of Australia’s forest is now formally protected in public nature conservation reserves. Multiple-use public forests, where timber harvesting is generally permitted, cover 9.43 million hectares, or about 6% of Australia’s total native forest estate.
A comprehensive legal, institutional and economic framework designed to achieve the conservation and sustainable management of forests is in place at the state, territory and national levels.
There has been rapid growth in forest certification as a means of verifying the quality of forest management and maintaining access to markets. In addition, most multipleuse public forests and some private forests are now managed in accordance with codes of forest practice and externally accredited environmental management systems, which provide a structured approach to the planning and implementation of measures to protect the environment.
MAKING LITTLE BITS OUT OF BIG BITS
Saw Milling – a very old industry
The Hierapolis sawmill, a Roman water-powered stone saw mill at Hierapolis, Asia Minor (modern-day Turkey) dating to the second half of the 3rd century AD is the earliest known sawmill. It is also the earliest known machine to incorporate a crank and connecting rod mechanism.
A sawmill’s basic operation is much like those of hundreds of years ago; a log enters on one end and dimensional timber exits on the other end.
Sawmills come in large variety of sizes, everything from portable plants that fit on a trailer to large softwood mills that take in a 100 semi trailer loads of logs every day.
Normally, sawmill size is measured in the volume (cubic metres) of logs that the mill will process in a year. Commercial hardwood sawmills that produce boards for flooring vary in size from around 7000m3 to 100,000m3.
Cutting Hardwood logs in dimensional timber also produces sawdust and waste products. The rule of thumb for recovery is a third of the log is produced into dimensional lumber, a third is produced into waste products like woodchip and pallets and the final third is sawdust.
IT TAKES TIME TO DRY OUT
Immediately after the sawmill cuts the timber it has a high moisture content of between 40 – 70%, as it is unseasoned (or commonly referred to as “green”). This high moisture content needs to be reduced to 9 – 14% (the Australian standard for Flooring) to achieve an acceptable flooring product.
Green timber has two different type of moisture – “free” moisture, which is around the edges of the cells and “bound” moisture which is in the cell walls.
As timber dries, the free water evaporates first, and the effect produced is principally a loss of weight. As the bound water is removed, the properties of the timber become noticeably change, the most noticeable being the dimensional size reducing.
As the free moisture leaves the cell cavity, it will eventually become empty, leaving the cell wall still saturated. This is such an important stage in the drying that it is given a special name, and the term is “fibre saturation” point
Stripping timber
To provide efficient circulation of air to all parts of the timber being dried in the stack, the layers of boards are separated from each other by suitable small sections of timber called strips, or stickers.
Size of strips – In thickness, the strips vary from12 mm to 25 mm. The use of thinner strips results in slower drying which might be required for a refractory timber, but thicker strips are suitable for most thicknesses and species. Strips about 19 mm thickness are most commonly used.
The strips should be made from sound, seasoned timber, and should be all thicknesses uniformly to’ the required size, otherwise the use of different thicknesses of strips will cause the boards to bend, resulting in warping.
Air Drying
The air drying process reduces the moisture content of the timber to the “fiber saturation point” which typically is around 18 -22%. This is the point when all the “free moisture” has evaporated.
The stripped out stacks are put into a specially prepared drying yard for them to air dry. This process for 25mm thick boards normally takes between 6 to 12 months.
Kiln Drying
Once the “free moisture” has left the board the bound moisture must be reduced to achieve the desired moisture content of 9 – 14%. This “bound moisture” is a lot more difficult to remove and thus the stack of timber that has been through the air drying process is then place in a large kiln (or Oven) where temperature and humidity are controlled over a period of 5 – 7 days. During this period the kiln will reach temperatures of 60 degrees celsius and the humidity can get as low as 40%. By modifying these controls in the kiln the operator is able to achieve the finished moisture content of the board.
Once Kiln dried the boards are now ready for production into finished flooring.
Written By: Malcolm Johnston | ATFA Editor