Please note! The orginial article contains pictures and can be downloaded here.
By: Per Friis Knudsen
The topic of wood science is a large one and something I will dive into several times in the coming year. We will explore the world of wood; what is wood, which wood for which uses and why we chose wood. My aim is to show how wood is more than just a business and an industry; to show how we all can benefit from wood. Wood has become more popular given its sustainable qualities and it has become the environmentally correct choice as it ties up CO2. All this and much more while still being an elegant and warm choice of natural material. Sustainability is in high demand and new products are constantly being developed that help the “green wave” on its way. In coming articles, it can be technical at times, but I’ll also give some examples and cases of how wood is used in a way I would never have thought could be possible.
Let’s dive deeper into the science behind wood. Which wood species our industry choose to work with changes consistently. It is based on important factors like world market, sustainability, political elements, competition, trends, and finally prices. In past years, factors such as world health, world economy, and global logistic factors have come into play. All this impact which kind of wood is in demand.
Our main business is hardwood. Hardwood comes from deciduous trees, which lose their leaves annually. Sometimes these are also called flowing plants. Hardwood is obtained through e.g. oak, beech, ash and walnut. These tend to be slower growing, which means that the wood is usually denser than e.g. softwood. Softwood comes from conifer trees which usually have needles and usually remains evergreen throughout the year. Softwood examples are spruce, pine, fir, larch, and cedar. In tropical regions, hardwood is also evergreen, but they do sheet their leaves one by one once a year. In Global Timber, we do supply some species of softwood such as radiata pine timber and spruce, douglas fir and pine logs, so don’t be shy to ask for softwood as well, especially if you are in need of logs.
Let’s focus on hardwood. The trend of exported species changes from beech to oak one year, and from ash to walnut the next year. The supply of some species was better some years back whereas the same species might be more difficult to source today. For example, American hardwood was a much larger part of our business just two years ago. There has also been a change in the demand for quality. Before lower qualities were in high demand, but now we see a movement towards higher quality wood. But as time changes and we change with it, demand will follow, so I believe the supply will continue to change depending on the market. We have already seen an increase in American hardwood in the last few months again in all qualities. In contrast, the African supply has become more of a challenge recently.
So, what is wood exactly? All types of hardwood consist mainly of cellulose and hemicellulose fibers that together give wood its strength and lignin that bond the fibers together (a glue-like substance). This makes up approx. 96% of heart and sap in the wood (see illustration below). In addition, 4% is inorganic and organic substances (e.g. cambium that is known for making the rays in e.g., oak and sycamore wood). The tree produces new sapwood and dries up the old sapwood and turns it into heartwood. Then mineral compounds from the soil form the cell walls. This makes the wood turn darker and gives the characteristic color for the given specie.
When it comes to cutting the wood, European and African logs are most often band-sawn “through and through” (live sawn = American term). It gives wider boards which we call “unedged”; this means that the edge of the boards is not square. It gives the boards their crown-grains (Cathedral) or irregular shapes in the middle and quarters-grains towards the edges. In America, sawmills tend to band-saw their logs into square-edged boards. You can say that the log is opened or sawn from one side first, they then turn and flip the log from side to side to produce the best yield possible and cut each board with square edged. This style often produces plain-sawn boards where some parts may go a little into quarter-sawn boards (see illustration below). This can be rather fascinating to watch, when a skilled worker uses modern bandsaw machinery to get the absolute best yield from every log. The process is often the difference between turning a profit or not.
However, there is always a BUT because wood is an organic material; a natural composite of cellulose fibers. Wood has characteristics and grains because trees are not always straight and grown in perfect locations. Some logs are grown near a river, some are grown on hillsides. Some in areas with more mineral soil that can give a variation in color called mineral streaks. Some grow faster in warm or slower in cold areas – or maybe sloping to the side if grown in very windy areas. All of the above have an impact as to how the tree grows and, ultimately, how the wood will end up looking. The wood will have a different look depending on the level of stones, sands, or mud in the underground or even the temperature variations. All of these scenarios make wood so interesting.
If we go further down in the scientific explanation, we come to the medullar rays in the wood. They are formed by the activity of cambium (as mentioned earlier). They appear as radial planar structures, perpendicular to the growth rings and are visible to the naked eye. Some manufacturers want to enhance the use of rays and, therefore, buy quarter-sawn lumber. Others might not want to see rays and, therefore, buy rift-cut lumber, where the cutting direction is supposed to minimize the appearance of rays.
These specific cuttings are slow to produce and give a lot less yield than plain-sawn lumber. Some mills specialize in this style of cutting and the price goes without saying at a very premium price. A few sawmills still produce true rift-cut lumber but at a very VIP premium price and seldom in larger volumes such as container loads. Typically, a true rift-cut hardwood is mostly done in the higher grade of FAS while in 1 common and 2 common qualities most times rift- and quarter-cut stays together instead of being separated. That mean customers get the best of both worlds from the full production, the rift, and the quarter at less of a price than a pure rift. In our Asian office, I have chosen to install both rift and quarter-sawn oak flooring to show visitors the difference in characteristics that wood grains can offer. It has all kinds of characteristics except for knots (see photo below).
Hopefully, these explanations have helped to shed a little more light into the scientific world of wood. As mentioned, the topic of wood science will occur several times in the coming year, so I hope you enjoyed the beginning of this series.