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Challenges and solutions in the protection of wood

Challenges and solutions for protecting wood exposed to moisture and weather conditions

Gregor Rep
Silvaprodukt d.o.o., Dolenjska cesta 42, 1000 Ljubljana

Climatic conditions in most parts of Slovenia are one of the most unfavourable for the use of outdoor wood on the European scale. High precipitation, high air humidity and moderate temperatures allow the development and process of moulds, fungi and other pests that cause marked discoloration (uneven darkness) of wood elements and their relatively rapid collapse. Despite this, in practice we encounter many examples of use of unprotected wood on both, public and private buildings. The used wood species, mostly spruce and domestic and Siberian larch without additional protection, are not suitable for outdoor use, as evidenced by the valid Slovenian and European standards. The consequences of wrong choices in the choice of wood and/or type of protective agent are often evident in a year or two after exposure, with first cracks and deformations seen on wooden objects and products and first signs of infection with wood pests.

Figure 1 and 2: Discolorations and deformations on the unprotected facade of a public building in Ljubljana

Normally, the aesthetic function of such a wooden product is usually at risk, and soon, often within three to five years, such a product loses its useful function and then completely decays.

Figures 3 and 4: Deformations and decay on wooden benches in Ljubljana

For users, decay of a wooden object is dangerous due to dry rot caused by the decomposition fungi. In the case of regular, but incorrectly performed maintenance work on the surface of wood, such a degradation is evident in some cases only after complete collapse and sudden break of the wooden element. In the case of larger wooden constructions such as roofs, wooden houses, wooden bridges, playgrounds in kindergartens, and the like, such fractures are life threatening. Although we recently had a number of such cases in Slovenia, even in public areas and facilities, we have not yet experienced serious human injuries.

Figure 5: Breaking of the wooden pylon of the swing during play in kindergarten

Appropriate basic wood protection for outdoor use can only be achieved with products and methods, which ensure that wood is protected even deeper to its core. Surface coatings (various paints, varnishes, glazes, etc.) applied to the wood by brush or spraying do not increase the resistance of wood to wood pests, but only contribute to decoration and slowing down greying process of wood. Steam-impermeable surface coatings can even considerably shorten the lifespan of a wooden product or object in our climatic conditions, as they slow down drying of the wood after precipitation, thereby accelerating its dry rot.

Figures 6 and 7: Rapid decay of a wooden fence due to use of thick-layer surface coatings

The effectiveness of various oils, which are often used in practice, is highly questionable, since only superficial application of any oil cannot protect the wood against fungal spreaders (rotting) and other wood pests over a longer period of time. The oils do not bind to the wood, which is why they will soon be rinsed out of wood. The lifetime of oil-protected wood is usually not longer than the life of ordinary, unprotected wood Moreover, extraction of wood oils causes additional inconveniences: uneven appearance of the surface (stains), pollution of the environment, the need for frequent reapplications of coating. Often, the used oils are an excellent nutrient medium for various moulds, which spread across wood even faster.

The European Union has very strict legislation on the use of wood preservatives (biocides). For quality preparations that are in accordance with Slovenian and European legislation, it is considered that they are proven effective in all climatic areas, that they are not rinsed off during precipitation, they are not harmful to humans, animals and the environment, and that they do not contain volatile organic substances. The only authorised and effective substance for protecting wood, exposed to the toughest conditions (precipitation, soil, running water or the sea) is copper hydroxide, which is allowed even for organic plant protection in organic farming. Similar preparations have been used for centuries in the production of vegetables and viticulture. High-quality wood preservatives, as already mentioned, even ensure that when wood is exposed to precipitation, it does not rinse off, which means they are completely safe for humans and the environment. By ensuring a significantly longer lifespan of a wooden product or facility, the use of such protective materials also contributes to the storage of carbon dioxide, forest conservation and sustainable development.

It is worth remembering that, in terms of choosing the type of wood, the type of protective agent and its use, it is sensible to consult experts, and that its aesthetic value and functionality throughout its life expectancy is more important than the initial appearance and colour of the building. Only this way will customers and users of wooden structures be satisfied, and these facilities will truly be pride of our cultural landscape.

Figure 8: Wooden bridge across the Krka River, protected with Silvanolin®

Figure 9: Wooden facade from thermally modified spruce Silvapro®