Pressure impregnation in an autoclave increases the strength of the wood. It is also done in Romania

Wood, used for building houses, fences, bridges and load-bearing structures, is a vulnerable material and can deteriorate for a variety of reasons, both indoors and especially outdoors. Its resistance to moisture, weathering, fungi, mould, insects, fire is different from species to species. However, resistance can be improved by treatment with various substances, and impregnating wood with insect-fungicidal substances makes it more resistant. Treated in this way, wood can be safely used for the load-bearing structures of houses or for exterior constructions that have to withstand weathering or the destructive action of UV radiation.

CASArbor, a house builder that also offers impregnation services

CASArbor is a manufacturer of wooden houses and fittings in Sfântu Gheorghe, which recently equipped its factory with an autoclave for impregnating wood. The strength requirements for wood used as a load-bearing structure or outdoors, especially from external beneficiaries, prompted this purchase. Until they had their own autoclave they had to look for solutions in the country, which were not always within reach.

The autoclave purchased has a large capacity and so they can also offer impregnation services to other house manufacturers or to those who do outdoor landscaping. The length of the beams or timber can be up to 12 m and the cross-section of the package put into the autoclave up to 1200 mm x 1200 mm. The maximum capacity of the autoclave is 17 m³ of wood and 31000 l of impregnation solution. Both softwood and hardwood can be impregnated.

CASArbor uses for impregnation Tanalith™ and Tanatone. Tanalith™ is used for protection (we'll talk more about this in a moment) and Tanatone is a staining product that stains wood in pleasant shades of brown. Both must be used to protect the wood. The colour obtained from treating the wood does not stay the same permanently. Over time it changes to a honey-brown tint and finally to a silvery grey. The discolouration, however, takes much longer and is uniform.

Benefits of insect fungicide treatments

Treating wood is done in several ways, the simplest way being to apply, with a brush or by spraying, substances that increase its resistance to attack by insects, fungi and moulds, increase its resistance to water and UV radiation. These are the classic treatment cycles that we have spoken on other occasions.

Until restrictions on these substances were introduced, insect fungicides were added to some materials used to weed wood. This protected the wood as well as staining it. Protection from moisture and sunlight was provided by varnishes and paints specially formulated to be resistant to the outside. However, over time it was discovered that some of the insect-fungicidal substances were dangerous to humans and as a result, a number of restrictions on their application were introduced. Insecticides are now placed under a special regime and are no longer mixed with finishing materials. Wood is treated with special substances for this purpose, after which the wood is stained and coated with protective materials.

These wood treatment substances are water-based and can be applied by brushing or spraying, by immersion or by pressure. The wood protection method with the best results is pressure impregnation. The substances penetrate deep into the wood increasing its strength. As a result of the treatments, in addition to resistance to insects, mould and fungi, the wood becomes more moisture resistant, dimensionally stable and dense. Pressure treated wood is also available in warehouses and stores. You can easily identify it by its uniform green or yellow colour.

Treating wood with Tanalith™

One of the most commonly used products for impregnating wood is Tanalith™. It's actually a family of products manufactured by the British firm Lonza Wood Protection which has proven its effectiveness for more than 20 years. Lonza Wood Protection is one of the world's largest manufacturers of wood protection materials. The company's tested, approved and certified products increase the strength of wood used in the ground or above ground. There are several strength classes, and the treatment is done so that the wood reaches the required strength of a particular class.

CASArbor works with these impregnation products to obtain wood with different degrees of strength. Classes resistance are determined according to subsequent use impregnated wood (sometimes you may also encounter the abbreviation UC 1...5, from "use class"):

• Class 1 - Wood used indoors in a dry environment (beams between floors, floor beams)
• Class 2 - Wood used indoors in areas at risk of damp (roof slats)
• Class 3.1 - Wood used outdoors, above ground and covered with paint or varnish (windows, shutters)
• Class 3.2 - Wood used outdoors, above ground, not painted or varnished (stone post fence)
• Class 4 - Wood in direct contact with soil or fresh water (fence posts, ploughs, trellises)
• Class 5 - Salt water wood for marine use (marine piles)

Tanalith™ E is a water soluble product based on copper and organic biocides (triazoles) that gives the treated wood a natural pale green initial colour. Over time, the treated timber fades slightly to a warm honey brown and finally to a natural silver grey. The treated wood - sometimes called tanned wood - is ihill for fences, terraces, pergolas, playground and construction applications, resistance to fungal, mould and insect attack being long-lasting.

How to do pressure impregnation in the autoclave at CASArbor

Wood impregnation is done in an autoclave, in a cycle that involves lowering, raising and lowering the pressure again.

1. The lumber is inspected, stacked and placed in the autoclave. The moisture content of the wood should not exceed 25%
2. The autoclave is vacuumed so that the air in the wood is removed
3. Impregnation solution is introduced until the autoclave is completely filled
4. Hydraulic pressure is applied so that the preservative penetrates as deeply as possible into the wood
5. The liquid is removed from inside the autoclave and returned to the storage vessel. Inside the autoclave a depression is created again
6. It returns to atmospheric pressure so that the liquid remaining on the surface of the wood is absorbed into the wood where there is lower pressure
7. The wood is removed from the autoclave and left outside to dry.

The difference between the strength classes is given by the duration of the whole impregnation process. This can be between 1 and 4 hours, depending on the species of wood, the thickness of the wood and its subsequent use (strength classes).

CASArbor does everything with dedication and commitment, trying to provide customers with prompt service in accordance with their needs and wishes, while respecting nature. It may seem strange, but impregnating wood is also part of the same idea of protecting and appreciating nature. Impregnated wood can be used for a longer period of time and its strength is greatly improved.