Challenges and solutions in wood protection

Challenges and solutions

Climatic conditions in most parts of Slovenia are among the most unfavourable for the use of wood outdoors in Europe. High amounts of precipitation, high humidity and moderate temperatures allow the development and activity of moulds, wood-decay fungi and other pests, which cause distinct discolouration (uneven dark colouring) of wooden elements and, in the worst case, their rapid decay. Despite the above, in practice, there are many cases of unprotected wood being used on both public and private buildings. The wood species used, most often spruce, domestic and Siberian larch, are not suitable for use outdoors without additional protection, as evidenced by the applicable European and international standards. The consequences of wrong decisions in the choice of wood and/or the type of preservative are very often already visible a year or two after the wood has been exposed, when the first cracks and deformations as well as first signs of infestation by wood pests appear on wooden objects and products.

Usually, the aesthetic function of such wooden products is compromised first, and shortly afterwards, often within three to five years, it loses its practical function and then decays completely.

The main danger to users is the collapse of the wooden structure due to decay caused by wood-decay fungi. Despite regular but incorrect maintenance work on the surface of the wood, in some cases such decay is only noticeable when the wooden element finally collapses and suddenly breaks. In the case of large wooden structures such as canopies, wooden houses, wooden bridges, playgrounds in kindergartens, etc., such structural faliures can also be life-threatening. Although Slovenia has recently had a number of such cases in public areas and buildings, fortunately there have been no serious injuries to people (yet), but there are known tragic cases from abroad.

Adequate basic protection of wood for outdoor use can only be achieved with products and methods, which ensure that wood is protected to its core. Surface coatings (various paints, varnishes, lacquers, etc.) applied to wood by brush or spray do not significantly increase the resistance of the wooden elements to wood pests, but mainly contribute to the decorative effect and slow down the greying of the wood. In our climate, vapour-impermeable surface coatings can even significantly reduce the lifetime of a wooden product or building, as they slow down the drying of the wood after precipitation, thus accelerating its decay.

The effectiveness of various oils commonly used in practice is highly questionable, as a surface application of oil alone over a long period of time cannot protect wood against wood-destroying fungi and other wood pests. Oils do not prevent the wood from becoming wetand thus from being colonised by wood-destroying fungi. The lifetime of wood protected with oils is therefore usually not significantly longer than that of untreated wood. Leaching of oils from the surface of also causes additional inconveniences: uneven appearance and staining of the surface, severe environmental pollution, and the need for frequent recoating. Often, the oils used in this way are also an excellent breeding ground for a variety of moulds that cause intense dark discolorations. Additionally, the surface of wood also becomes significantly darker due to applpication of oil, consequently causing more cracks on the surface due to more intense heatup form solar radiation.

The European Union has very strict legislation on the use of wood preservatives (biocides). Quality products that comply with Slovenian and European legislation are proven to be effective in all climates, do not leach from wood when exposed to precipitation, are not harmful to humans, animals and the environment, and do not contain highly volatile organic substances. The only substance that is still allowed and effective for the protection of wood exposed to the most severe conditions (precipitation, soil, running water or the sea) is copper hydroxide, which is even allowed for plant protection against fungi in organic farming. Similar products have also been used for centuries in vegetable growing and viticulture. Quality wood preservatives, as mentioned above, even ensure that copper does not leach out of wood even when exposed to precipitation, which means that they are completely safe for humans and the environment. While ensuring a significantly longer lifetime for a wooden product or building, the use of such preservatives also contributes to carbon sequestration, forest conservation and sustainable development.

It is worth remembering that it is wise to consult experts when choosing the type of wood, the type of preservative and its application method, and that what matters more than the initial appearance and colour of a building is its aesthetic value and functionality over its entire expected lifetime. This is the only way to ensure that the customers and users of wooden buildings will also be satisfied and that these buildings will truly be a pride and a decorative asset to our cultural landscape.