Fir wood – Determination of guidelines for the first and second processing stages to prevent damage to wooden components
WHFF Project 2018.16
Project Management: Thomas Volkmer
The most important facts in brief
- Different fir assortments are investigated with regard to wet heartwood and red streakiness in its effects on product quality and especially biological stability
- Grading criteria and guidelines for storage, transport and drying of fir wood to prevent leaf blight infestation are established
- It was shown that fir wood has a similar resistance to the fir leaf blight as spruce wood and that fir wood is well suited for use as façade material
- The decisive factors, however, are above all the correct use, the construction details and the quality of the workmanship
White fir (Abies alba) is ideally suited for timber construction and is predestined for aesthetically demanding components, such as facades. Compared to spruce, it has significantly fewer knots and no resin. In contrast, there have been more cases of damage in the recent past where fir trees have been attacked by the fir leaf blight.
Against this background, different fir assortments of the planing mills involved in this project were investigated with regard to wet heartwood and red streak in its effects on product quality and especially biological resistance. By answering the question: “In which form can various fir assortments with possibly quality-reducing properties (wet core, red streakiness) be safely used?”, processing guidelines were defined in this context, which guarantee a maximum service life of the components and thus prevent damage to wooden buildings. In the present project, the first two processing stages from felling onwards were specifically investigated: Storage, cutting, grading, and drying.
Regarding the general susceptibility and a possible attack of fir wood (without wet core and red streak) in comparison with spruce wood, it can be said that there are no significant differences. Both variants are degraded to the same extent, whereby spruce even showed the greater degradation rates.
With regard to the different fir assortments, the same applies in principle, that the red streakiness or the presence of the wet core led to a stronger infestation can also not be confirmed, also because the values vary and partly overlap.
It remains to be emphasized, however, that these results refer only to laboratory tests and accordingly cannot be transferred without further ado to wooden elements in the outdoor area. Nevertheless, it should be noted that fir wood has a similar resistance to fir leaf blight as spruce wood.
However, it is primarily the constructional details which are responsible for the susceptibility. If fir wood had been used in accordance with the state of the art, the frequent damage would have been largely avoidable.
The general climatic and local conditions on site should also not be forgotten in this context. Accordingly, however, it is particularly important that in humid environmental conditions (north-west orientation, strong vegetation, shading, etc.) care is taken to ensure that the structural details are planned and executed very carefully. This is of great importance because the infestation and the present damage cases result from a combination of different circumstances: Construction details, quality of execution, type of surface treatment, among others.
In summary, it can be said that fir wood is well suited for use as facade formwork and, if used properly, can be expected to have the same durability as spruce wood. It should be taken into account that fir wood is not expected to show resin spills and that its aesthetic appearance is significantly better than that of spruce. Since fir facade formwork is usually cut from comparatively thick logs and is not made from core-separated rough planers, significantly fewer cracks and warping can also be expected than is usual with spruce.
The project was supported by the Swiss Forest and Wood Research Promotion WHFF-CH of the Federal Office for the Environment BAFU.Download