- How does firing affect wood
- Ornamental value of burnt wood
- What species and what type of wood is better to burn
- Charcoal firing in the field
- How to burn wood with a gas burner
- Finishing of charred wood
In modern construction, wood is usually treated with chemicals. But after all, houses of wood were built before, and some of them stand to this day. We invite you to get acquainted with the method of wood processing by firing and find out what is the advantage of this method.
How does firing affect wood
As the subcrustal layers of the tree grow, year after year, its fibrous cells die off due to the pores that form. The high porosity, in particular, explains the hygroscopicity of wood – its ability to absorb and release water molecules, depending on the difference between its own humidity and the water vapor content in the ambient air..
The structure of wood fibers is always uneven: in the process of life, cellulose polymers of varying degrees of stability are formed in the tree, as well as sugars and resins of all kinds. It is the presence of pores and organic nutrient residues that determine the main disadvantages of wood: flammability and the presence of a nutrient medium for the development of bacteria and fungi..
The ability to “seal” wood from the influences of the outside world still exists. It is used during creosote cooking of wood or in the autoclave heating process (thermolysis). When heated to 300-400 ° C, almost all unstable hemicellulose formations are destroyed, and in fact they serve as a “launching pad” for the ignition of a tree (forming the primary volume of flammable pyrolysis gases), and as an initial nutrient medium for the development of colonies of harmful organisms.
At home, such wood processing is incredibly difficult to reproduce. But it is quite possible to partially clog the internal pores and remove most of the unstable cellulose polymers. Even superficial firing is capable of heating up the outer layer (5–20 mm) of wood enough to melt lignin and resins and form an inorganic crust that protects against most external influences. After proper firing, it is practically impossible to re-fire the wood without intensive and prolonged heating to 500–700 ° C. At the same time, the residual heat kills microorganisms remaining in the thickness of the tree, and the sintered outer layer does not allow the penetration of pathogenic organics from the outside..
Ornamental value of burnt wood
Much more interesting is the visual effect of burning wood. It was thanks to him that the technology of processing wooden beams under the fancy name “Shu-Sugi-Ban” was born in Japan, and everyone is well aware of the Japanese meticulousness in interior design.
The appearance of wood processed in this way directly depends on the technique and depth of firing, and there are three types of them. The first – surface firing – allows you to create a brown-brown surface with a golden sheen, on which the wood texture appears quite contrasting. The chemical and biological resistance of such wood is not high enough, therefore, surface-fired products are used, as a rule, in interior decoration. Due to the fact that the impact on the structure of the tree is minimal, because the firing affects only 2–5 mm below the surface, the finishing materials can retain their lightness, that is, it is quite possible to process ordinary lining in this way.
Deep firing of wood is used for older lumber, often for planks and beams that were already in use. This technique helps to “renew” the wood: to remove the dried surface gray layer and to warm up the entire thickness of the wood qualitatively. Due to this, the surface acquires a very expressive appearance: from iridescent graphite to coal-black imitation of rare noble rocks. Perhaps, such a depth of black color cannot be achieved by other methods, because deep-fired wood is so highly valued by designers.
The third degree of wood processing is its complete burning. Actually, it ceases to be a tree altogether, turning, in fact, into a polymer-carbon plastic. At home, unfortunately, it is almost impossible to perform a complete firing: during the charring period, the fire will have time to eat almost half the thickness of the workpiece. This wood is used primarily in the manufacture of furniture. The technique guarantees the absolute uniqueness of each product, because the characteristic pattern and formed splits cannot be reproduced again..
What species and what type of wood is better to burn
Any tree is generally suitable for firing, but connoisseurs of subtle visual delights will most of all like breeds with an expressive and unusual texture. The original technology of Japanese origin used exclusively cedar. Burnt hornbeam and beech boards have an interesting look: due to the high density of such a tree, only its top layer burns out, due to which anthracite and gray color overflows are achieved.
The more popular valuable species, such as alder, maple and poplar, exhibit an elongated texture after firing, while walnut or larch can form additionally smaller texture patterns. Burnt birch will be appreciated by lovers of baths or saunas: due to firing, its surface becomes very porous and acquires a low heat capacity, therefore, after heating it does not burn the skin.
It is also surprising that, depending on the degree of burning and the origin of the tree, even the same species can manifest itself in completely different ways. A thorough approach should be taken to the use of charred wood in decorative finishes: stock up on samples of different types from different sources and, after a series of experiments, come to a certain choice.
Remember also that the wood must be properly prepared before firing. It should have a low moisture content, preferably no more than 12-13%, and also be natural, that is, without traces of painting and opening with drying oil. Otherwise, the absorbed resinous substances will appear unevenly on the surface and disturb the appearance. Of course, a lot here depends on the depth and time of fire treatment..
Charcoal firing in the field
The easiest way to carry out firing is best suited for deep firing. In this way, decorative beams are processed, as well as wooden siding and a block house for outdoor decoration. Due to deep heating, the wood becomes immune to atmospheric influences, and the influence of sunlight on it does not affect it at all.
For charcoal firing, a narrow trench should be dug about 30 cm deep and width corresponding to the dimensions of the workpiece. A fire is made in the ditch, and as it burns, the wood is constantly stirred, achieving their rapid charring. After that, the ditch must be covered with either sheet metal or an OSB strip in order to temporarily prevent the access of oxygen and stop the combustion.
Before laying the workpiece in the coals, you need to rake out the central groove so that not only the lower part is processed during firing, but also small areas on the sides. Exposure of the workpiece depends on the thickness and can be from two to three to fifteen minutes. After that, the workpiece is turned over to the opposite side, and then, after maintaining the same period of time, it is burned out on the sides.
It will be easier to remove the workpiece with a pair of steel wire hooks. After the tree is removed from the coals, it is immediately doused with water..
How to burn wood with a gas burner
Using gas burners is much easier. These can be both hand-held camping lamps, and ordinary nozzles connected to the cylinder via a hose..
It is convenient to use gas to treat wood only with superficial burning. Deeper fire holding will not be uniform enough, resulting in variable thickness and width. In addition, a lot of gas is required for deep heating, while coals cost almost nothing..
For surface treatment, the wood is touched with the very edge of the light blue torch. The movements are conditionally the same as when painting. At the same time, it is quite easy to control the firing depth by the degree of darkening.
Firing is followed by wetting, but in this case, a conventional hand spray will suffice. It is important that the time between fire treatment and spraying with water is the same for all areas of each part, so treat in sequence.
Finishing of charred wood
After the wood has cooled, carbon deposits and soot are removed from it. Brass wire brushes are used for this, so as not to peel off excess. In the course of mechanical processing, invoicing or the so-called artificial aging of wood can also be carried out..
Cleaned products can be mounted immediately. Additional processing is needed not so much to protect the structure of the tree, but to preserve its color and appearance in general after years, as well as to eliminate soiling. For interior decoration, the lining is covered with linseed or hemp oil in several layers. Wood for the facade and other external work is covered 1-2 times with a colorless nitrocellulose varnish with the addition of synthetic wax: either with a brush along the grain, or with a spray gun.