Cycle and protection of wood as a natural building material
Wood is highly durable by nature. If it is installed dry and kept dry during construction, it can last for many generations. In areas with high humidity, wood can be protected by construction measures or various treatment methods. In addition, wood can be excellently combined with other materials and is easy to refurbish and recycle.
Wood, people and nature in the cycle
The natural cycle knows no waste. Dead trees are decomposed by fungi, microorganisms and insects. Heat and a wood moisture content of over 20% accelerate this process. If these factors are missing, decomposition can take centuries. Egyptian burial objects made of wood have survived for 3500 years, as have many wooden houses in Switzerland that are hundreds of years old. One example of an old wooden building in Europe is the 800-year-old Nideröst House from Schwyz, the core of which dates back to 1176.
Preventive wood preservation
To protect wood from pests and fungi, it is crucial to keep the wood moisture content below 20% and keep it dry. Constructive wood preservation allows wood to be used in humid environments by allowing it to dry quickly after it has become wet. Protection starts at the planning stage by taking measures against the effects of moisture. Canopies and well-executed plinth areas effectively protect against moisture, and precise details on windows and balconies are essential for long-term durability.
Natural resistance vs. chemical protection
In the event of increased stress, you can opt for a type of wood with natural resistance. The heartwood, which is preserved with natural substances, is more durable than the sapwood, which is enriched with sugar and nutrients. There are transparent to opaque protective coatings, which are particularly necessary for exterior components such as windows. In protected areas and interiors with a wood moisture content of less than 20%, chemical wood protection is not necessary. However, if the moisture load exceeds the natural resistance and no constructive solutions are available, the use of chemical wood preservatives remains as a last resort. Nowadays, coloured pressure impregnations without chromium are an environmentally friendly solution for chemical wood protection.
Changing the molecular structure
The aim of processing wood is to change the molecular structure of the material in such a way that it becomes more difficult for microorganisms and insects to break down the wood. Water absorption is also reduced. Thermowood is produced by intensive heating at temperatures between 170°C and 250°C over a period of 24 to 48 hours. Acetylated wood is produced by pressure impregnation with acetic anhydride, while furfurylated wood is produced by furfuryl alcohol. Thermowood has a smoky odour after production, whereas acetylated wood smells of acetic acid. Modified wood has altered static, optical and hygroscopic properties.
Façades as a protective shield
The outer shell of a building, also known as a façade, is not only used for decoration, but above all for protection. Depending on the location and orientation of the building, the façade is exposed to various weather influences. A professionally installed façade protects the building structure from damage caused by mechanical influences and moisture, drains water and thus ensures that the wooden parts dry quickly. Ventilated façades also promote the drying of the façade cladding and the load-bearing structure.
Pre-greying process
UV radiation and free radicals decompose lignin and cellulose in the wood, resulting in lignin being washed out and light-coloured cellulose remaining visible. A microscopic film of grey fungi forms on weathered façades, leading to uneven grey colouring. For this reason, façades are often pre-greyed to ensure a uniform grey colour.
Treatments for wooden façades
Pre-greying treatments have proven to be an effective method of matching directly weathered façades to the aged colour from the outset. This bridges the large colour differences during the ageing process of untreated surfaces. There are different variants of pre-greying treatments with different properties. In particularly protected and highly exposed areas, pre-greying treatments tend to turn brown again over time.
Natural wood façade ageing
In natural pre-greying, the façade parts are placed horizontally in the sun and exposed to rain. Specialised manufacturers accelerate this process with the help of additional enzymes. This process takes around six months.
From glazes to Swedish colours
The use of glazes is one of the semi-transparent wood treatments. If they do not form a closed layer, they are considered non-film-forming. Paints belong to the opaque treatments. Varnishes are particularly closed to diffusion, while Swedish colours are considered to be particularly open to diffusion. To ensure a good bond between the surface treatment and the wood surface, the application should be carried out mechanically in the factory. Façade formwork with a rough-sawn or textured surface is therefore particularly suitable. Pressure impregnation with added colour is also a semi-transparent treatment and does not form a film. Colourless technical treatments such as additional hydrophobisation as a finish, impregnation or UV protection treatment can further extend the maintenance periods and serviceability.
Long-term protection
It is important to maintain painted wooden façades regularly to ensure their longevity. Maintenance instructions from a specialist are extremely helpful. The intervals for maintenance depend on various factors such as the product used, the wood protection, the location and the environment.
Variety of timber house façades
Not every timber house reveals from the outside whether it is actually made of wood or not. All architectural design forms are conceivable in the field of timber construction. In addition to wood, the façades of timber buildings can also be clad with glass, metal, plastered cement panels or plastered thermal insulation composite systems. Combinations of materials can have a particularly aesthetic effect in timber construction.