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Was ist Harz?

What is resin?

What's the sticky stuff on the wood?
The sticky residue you can see on the surface of wood and wood products is resin. Resin occurs in wood either as a natural substance or as a result of injury to the tree during growth.

When naturally occurring, it adds to the character of the wood. In these circumstances it can be present in sufficient quantities. Wood with naturally occurring resin is used where the effect of the resin is to be used, e.g. B. when increased natural durability is required.

The other form of resin is the result of physical or natural injury to the tree. These can occur on branches that have not yet fully grown into the main trunk of the tree. Occasionally, physical injury can lead to the formation of resin pockets in the tree. Also, when bark beetles invade, resin leaks out to eliminate the attackers.

The wood we use to make general cabinetry is typically selected to be free of naturally occurring resin. However, resin formed as a result of injury to the growing tree may still be present.

After processing, the wood no longer produces new resin. During the aging, drying and selection process, wood with obvious pitch pockets is sorted out. Joinery standards permit the cutting out and repairing of pitch pockets in joinery products where practicable.

appearance of the resin
There are various reasons for the unexpected appearance of resin at a later stage of wood products. Resin contains naturally produced oils. Over time, these will evaporate and the resin will harden. If the wood is left standing for an extended period of time, all of the resin in each piece of wood will fully harden. However, in modern carpentry it is not practical to store wood for this period. Drying in the drying chamber, used to reduce the moisture content of wood, helps to pull out the resin that has reached the surface and remove it at an early stage.

Softwood intended for outdoor use is often treated with preservatives, usually an organic, solvent-based preservative. This process is not affected by the presence of resin, nor does it attack the resin.

The problem of resin exudation usually occurs only after the surface coating has been applied to the finished wood product. It can also take a few years for it to appear.

Fine pathways to the resin pockets can be exposed through the machining process. Certain parts of a joinery product can be heated either by local heat sources or direct sunlight. Inside, controlled heating systems can raise the surface temperature of wooden components just enough to pull the resin to the surface. Outdoors, a combination of direct sunlight and dark finish systems can also increase the temperature and cause the resin to flow.

The resin that comes out can show up on the surface in two ways. If a microporous paint or stain has been used, the resin may bleed through the surface. If a non-porous paint has been used, the resin will lift the paint from the wood and reveal the underlying surface. In both cases the wood can be left in place until the flow of resin has stopped. However, this is not a very satisfactory solution when the wood is exposed to the elements or when the aesthetics of the structure are destroyed.

resin on the wood

How to remove the sticky residue on wood?

Removing resin from paneling, windows and doors and other outdoor wood products.

It may be possible to get more resin onto the surface by washing off the existing resin and gently heating the surface of the wood with an electric lamp or heat gun. The surface resin can be removed by gently wiping the surface with a lint-free cloth dampened with denatured alcohol. If the wood is coated with microporous paints, this procedure, if done carefully, can avoid repainting.

If no microporous paint or stain has been used, the best solution is to allow the resin to cure on the surface. This can then be removed by gently scraping it off. During the time that the resin is moving, the finishing system continues to perform its function and does not need to be repainted until the cured resin has been removed.

If the equipment system has been raised, another solution must be used. It is preferable to leave the resin as before until it has hardened, then scrape it off and refinish the bare wood surfaces with a full finishing system. However, this method can only be used if the wood is not exposed to the weather. Protection of exposed wood must be done as soon as possible to prevent moisture levels from rising and further coatings peeling due to excess moisture.

There is no guarantee that resin will not leak out and damage a piece of furniture's decoration.

Shellac knot solution was used in the past, but it is only intended to reduce the contamination of the coating system, but not to eliminate it. You can never be completely successful as modern coating systems are designed to be flexible. Either they don't stick to the knot or the resin forces the decor to detach from the wood.

Once the resin has reached the surface and the above measures have been taken, the problem is unlikely to recur.

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