Utilisation of the sweet chestnut

The sweet chestnut is a "heartwood" tree and as such, it has a consistent development of coloured heartwood and there is a significant difference in colour between heart and sapwood. The narrow sapwood is a dirty white to yellow colour and freshly cut sapwood is yellowish brown or light brown. Under the influence of light it will darken to a light brown till dark brown tone. The wood of the sweet chestnut belongs to the ring porous wood species and is optically very similar to oak. On the cross section, however, wood anatomical tests reveal the differences quite well. Characteristics of sweet chestnut are the tender flame tracts and the very narrow wood rays, which can only be seen through a magnifying glass and are usually arranged in single rows (Fig. 1.).

The early wood pores are very large with multiple tylosis and appear quite oval under the microscope (Fig. 3). They can be seen as characteristic pore grooves on the cross-section and on the tangential areas with the cathedral effect (Fig. 2). In comparison, the late wood vessels are very small and ordered in small rows which are narrowly radial to oblique and often forked. Axial parenchyma is only sparingly present in the basic fibrous tissue and can be seen as a strand with two to five cells (Fig. 3). The wood rays are exclusively arranged in single rows and are thus not to be detected on a macroscopic scale. (Fig. 1 and 2).

The density of chestnut wood lies within the average but slightly below the well-known domestic broadleaved species (Tab. 1). The unusual feature combination "durable and elastic" is well expressed in the mechanical characteristics of the wood: The tensile strength is 135 N/mm², the rigidity is extremely low at 9.000 N/mm². As a result, the flexural strength of 80 N/mm² is lower than the broadleaved trees listed in Table 2 and the wood of the pine tree. Values for hardness are also significantly reduced.

The moisture-physical behaviour of the wood is a positive characteristic for the utilization of the wood. Both, volume shrinkage and differential shrinkage / swelling, are low in comparison to other types of wood (Tab. 3) and results in a good dimensional stability. The water vapour permeability is low, the fibre saturation humidity is below twenty-two percent.

The high content of acid (pH of the heartwood <4) leads to corrosive discoloration in contact with ferrous metals in damp environments. The wood of the sweet chestnut possesses a good natural durability (class 2 according to EN 350).

In order to judge how the wood should be used, the round wood characteristics of how the sweet chestnut grew in the forest should be taken into consideration. Wood shake can be a problem with sweet chestnut and can devalue the wood for lumber production (Fig. 4). As a result, the production of quality wood from the sweet chestnut has to be consistently adapted to the local site and climate conditions in order to guarantee that abrupt changes in growth can be avoided (in particular during juvenile growth).

For the various assortments of sawn lumber the moisture should be reduced slowly in order to reduce the danger for cracks and warping. Cell collapse is possible if the drying gradient is too high. The dried wood is easy to work (sanding, polishing, turning, drilling) and shows a satisfactory to good behaviour on the surface and in finger joints.

For the production of quality wood and veneer the round wood trunk has to possess a sufficient level of quality and dimension (<D4). Veneers for knives are produced from high-calibre wood. Additionally, the straight growing and knot free wood of exceptional quality can be successfully marketed for window and door construction, the production of staves as well as interior and exterior construction timbers.

Sweet chestnut wood has been and will continue to be used as a locally growing source of timbers in house construction, especially in the Mediterranean countries. Lower quality assortments are valued in gardening and landscaping as well as in the production of decking boards, garden furniture and flooring in moist areas. The thin heartwood of the sweet chestnut is milled for the creation of posts and palisades and can be used in contact with the earth and water without chemical protection or modification treatments. The good tolerance of the wood to be painted makes it treasured by creative artists (Fig. 5). Similar to the black locust, the sweet chestnut is used untreated for protective constructions against creeping snow and avalanches in the form of tripods and has a life expectancy of thirty years (Fig. 6).

In the wood material industry sweet chestnut can be used for the creation of particleboard and fibreboard in principle. Usage as an OSB board in construction was unsuccessful. In the future, the sweet chestnut will be given more attention by the bio refineries.