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When and how to protect wood


When designing a wooden product or facility intended for outdoor use, it is necessary to ensure that the wood gets as much protection as possible from rain and water and that it has conditions to dry fast. Parts of wood which are never dry, or get dry hard (like parts in joints between wooden components) present the greatest risk for infection with fungus which consequently causes rotting of wood.

Only healthy and dry wood should be selected for products or objects meant for outdoor use. Non-resistant and poor-resistant types of wood need to be thoroughly protected in depth. For this purpose, we can use effective basic protective agent for wood, or special heat treatment process - thermal modification.

When protecting the wood with liquid preservatives, instructions and recommendations from the manufacturer comply, since only large enough quantity of preservative and sufficient depth of its penetration ensures effective protection against insect. ¸Preservatives for basic wood protection should not be diluted, as this reduces their effectiveness. Applying basic preservatives on wood with brush does not provide adequate protection; often such procedure even shortens the life span of wooden product. Surface coatings (various colors, varnishes, stains, etc.) do not increase the resistance against wood pests, but only contribute to the decoration and deceleration of wood graying (which is a natural and harmless process).

When using wood in the open, a basic protective agent has to penetrate sufficiently deep into the wood.

For less exposed outdoors wood (e.g. the roof truss, cornices, wooden lining under the roof) it is usually sufficient to protect the wood by spraying or splashing of protective agent onto the wood. For more exposed/burdened wood (e.g. cladding, garden fences, etc.), we recommend soaking the wood in preservative in special troughs (e.g. Wooden, coated with foil) or pools where protective agent penetrates few millimeters into the wood. If the timber is meant to be in constant contact with liquid water, soil, or even sea water, it is necessary that the process of preservation is carried out by a qualified technician. In these cases special equipment for vacuum-pressure impregnation process is needed which provides sufficiently effective protection of wood against wood pests.
Equipment for in depth impregnation with wood preservatives (a pool and a chamber for vacuum-pressure impregnation).

Procedures, for basic protection of wood against wood pests, are divided into:
- Preventive - when practicing protection for the first time in order to prevent colonization of wood pests
- Further - we repeat protection process in order to renew or increase the effectiveness of preventive protection
- Curative - when practicing protection for the first time or repeating it in order to eliminate wood pests that are already present in/on the wood

In Silvaprodukt we provide effective means for basic protection of wood (Silvanolin, Silvanol), services of soaking wood, wood impregnation in the vacuum pressure chamber and the service of thermal modification of wood by procedure Silvapro®.

Our experts can be consulted about subsequent and curative wood preservation and also on rehabilitation of housing and other facilities infected (attacked) by fungal decomposition or other wood insect.


Outdoor wood is particularly vulnerable from living (biotic) factors of degradation, among which the most dangerous are decay fungus that cause wood rot. When conditions are favorable (wood humidity above 20%, moderate temperatures), wood can degrade within a few months. In this respect Slovenia has one of the most unfavorable climates in Europe, as conditions for developing wood rot are favorable most of the time.

Non-resistant types of wood (beech, spruce, fir, pine, larch, etc.), which are abundant in Slovenian forests, can be effectively protected only by the means and procedures for base, in-depths wood protection. On what basis do we decide IF and HOW do we protect our wood and which protection is necessary and appropriate?

First, it is necessary to determine to which extent will our wood or wooden product be exposed to moisture and wood pests:
1.:wood will be used in a covered space and its humidity will be consistently below 20%
2.:wood will be used in a covered space and its humidity will occasionally be more than 20%
3.:wood will be used outdoors and its humidity will be occasionally or often above 20%
4.:wood will be used outdoors, in constant contact with the ground, soil or running water
5.:wood will be used outdoors, in constant contact with salty sea water

We also need to know the natural resistance of the type of wood that will be used:
non-resistant types of wood: e.g. beech
poorly resistant wood species: e.g. spruce, pine
medium-resistant wood species: e.g. larch
resistant wood species: e.g. Chestnuts
very resistant wood species: e.g. black locust
When deciding, whether the protection of our product/object is necessary or not, we use the following table:
When non-resistant and poorly-resistant species of wood are used outdoors, a suitable basic preservative (e.g. Silvanolin) or a method of deep wood impregnation (e.g. Silvapro®) should be used. For medium-resistant wood species same measures are also highly recommended (e.g. larch), as the climate of most Slovenian towns (heavy rain, high humidity, moderate temperatures) allows rapid development of wood pests and consequently decay of wooden products and facilities.


Wood is a natural and renewable material that is degradable in nature. Decay of wood is caused by non-living (abiotic) and living (biotic) factors. When using wood for economic purposes, we want to suppress or stop that process as best as we can.

Among non-living factors of decay are: climatic factors (precipitation, UV light, temperature changes, etc.), air pollution (gas, solid particles) and fire. Abiotic factors affect especially aesthetic appearance of wood, rarely its mechanical properties. Graying of the surface of the wood for example is caused by solar or UV light, but does not affect its mechanical properties. Wood can usually be effectively protected from non-living factors of decay with suitable surface coatings such as Silvanol stain B.

Unprotected and surface-protected spruce board after a few months of exposure to sunlight and precipitation.
Much more dangerous, especially when using wood outdoors, are living factors of decay. These are organisms that feed on wood, or it plays a crucial part in their own survival. These include decay fungus (e.g. decay fungi, fungi modrivke, molds), insects (e.g. larvae of wood insects also called "Wood worms" and termites), bacteria and marine pests. In Slovenia, by far the most damage to the economic and finished wooden products and buildings is caused by wood-decay fungus. Due to favorable conditions (wood humidity above 20%, moderate temperatures), wood can decompose/decay within a few months. In this respect, Slovenia has one of the most unfavorable climates in Europe, as the conditions for wood decay are favorable most of the time (high rainfall, high humidity, moderate temperatures).

Wood-decay fungus in/on wood forming mycelium and also hats.

Larvae ("worm") and adult wood insect specimen (house longhorn beetle).

Not even modern wooden houses are safe from decay fungus, as we meet a number of cases where the fungi, due to minor or major errors in building/preparation process of wooden materials, completely destroyed the unprotected wooden structure within a few years after building got occupied. Reconstruction of such damage is extremely costly and time-consuming. To effectively protect the wood against the degradation from living (biotic) factors, we have to use effective basic protective agents (e.g. Silvanolin or Silvanol) and ensure their in-depth wood penetration. Appropriate method of protection and the depth of penetration of the protective agent are determined according to the exposure and features of the wooden product or object. Excellent alternative to the classical base preservatives for wood is Silvapro® thermal modification of wood.

Some examples of damage caused by fungal decay (rot wood)