Ville Liimola, Chief Sales Officer
As the pine ages, its oldest cells die and heartwood begins to form in the core part of the trunk, which is distinguished from the sapwood by its darker color. The color change becomes more clearly visible with the effect of the UV rays of light.
Heartwood differs from sapwood in its properties, as it contains less water, is denser and develops new substances that act as natural wood preservatives. The heartwood of pine trees is a particularly effective raw material for the wood industry. Instead, for example, the heartwood of soft leafwoods and spruce is not more durable than the sapwood.
In Pölkky’s procurement area, in northern Finland, the proportion of pine heartwood is particularly high.
Relatively more heartwood is produced in northern growth conditions compared to forests growing further south. In the north, there is a shorter growing season and a correspondingly longer time when the tree rests in winter. A harsher soil also affects the growth rate. These factors affect the thickness of the growth ring and produce dense wood material. In northern growing conditions, trees grow more slowly, but at the same time their heartwood share increases.
Characteristics of the heartwood
Extract substances naturally present in the heartwood, e.g. terpenes and resin, are poisonous to insects and protect the wood from insect damage. On the other hand, the heartwood no longer has nitrogen, which is why it is not a suitable growth medium for decomposer fungi, as it does not provide them with suitable energy. The blue stain fungus also does not attack the heartwood.
The cells of heartwood are closed, and therefore they also do not receive or release moisture, which would normally cause the wood material to shrink and expand. So the heartwood has a significantly less moisture variance and is more stable compared to the sapwood.
Wood, especially pine, has also been found to be an antibacterial material. Tiina Vainio-Kaila from Aalto University studied the antibacterial properties of pine and spruce in her doctoral research(1), and concluded that they are effective even against the hospital bacteria MRSA and VRE. Pine heartwood is generally more antibacterial than sapwood or spruce.
Durable raw material for long-lasting use
Due to their good rot and weather resistance, products made from heartwood are long-lasting and bind the carbon bound to them for hundreds of years.
The durability properties of pine heartwood have long been used in construction, for example in the manufacture of doors and window frames. There are still more than 100-year-old wooden houses with original windows. The wood used for them was from slow-growing pines with a high heartwood content, and that is why they are still in use today. It could be said that the production of sustainable wooden products is a traditional knowledge in Finland.
Today, heartwood is used to make e.g. doors, window frames and garden construction products, where resistance to weather conditions plays an important role. Heartwood’s characteristic darker tone combined with durability and less moisture variance makes it an excellent raw material for floorboards as well.
With the inherent durability of heartwood, it is also possible to avoid the use of chemical wood preservatives, which are poorly absorbed by heartwood anyway. Instead, the products gray beautifully over time. The properties do not need to be improved with chemicals – it is a genuine natural product.
Heartwood products in Pölkky’s production
All logs arriving at Pölkky’s production are X-rayed, which also shows the heartwood part of the timber. Based on this information, it is possible to choose suitable trees for each purpose, for example parts with a high heartwood content for the window industry or products for garden construction. Good raw materials combined with high expertise and modern technology produce high-quality products that perfectly suit our customers’ needs.
Our sales team will be happy to help you choose the wood products that suit your needs – contact us and we’ll discuss more!
(1) Source: Tiina Vainio-Kaila: Antibacterial properties of Scots pine and Norway spruce, 2017, https://aaltodoc.aalto.fi/handle/123456789/28650
