Wood oil for exterior and interior work: features of choice and application

Recommendation points

• Natural and mineral oils
• Used types of additives
• Oil application and curing
• Rubbing impregnation
• Multi-layer application and combination of oils
• Oiled wood care

There are many types of wood impregnation oils. In the carpentry business, the ability to choose the right composition and perform high-quality impregnation are on a par, both of these stages are equally important. We will tell you about the intricacies of processing different types of wood with oil in our new review..

The process of stabilizing wood with oil is extremely poorly covered in network sources. With a sufficiently detailed description of the application technique, which is already quite obvious, the principles of oil impregnation, the subtleties of working with different types of oils, as well as the behavior of the treated surface under different operating conditions are very rarely disclosed. And most importantly, the issue of alternatives to expensive impregnation compositions and the ability to prepare natural drying oil with special additives yourself is absolutely not covered..

Natural and mineral oils

To make the right choice of stabilizing compound, you need to have a solid understanding of how oil impregnation works. Its essence lies in the formation of a dense viscous substance from a flowing oil, which almost completely limits the capillary migration of moisture, and also deprives wood of its nutritional value for insects and microorganisms..

Not every oil is capable of behaving this way. For varieties of plant origin, the key role is played by the content of glycerides of linoleic and linolenic acids, which are capable of hardening under various external influences, forming long polymer chains. The highest content of fatty acids is found in linseed oil, slightly less in hemp. Tung oil is not highly saturated with glycerides, but in various combinations with other types of oils can create a stronger and denser polymerized mass.

Hemp oil

Under natural conditions, the oil hardens extremely slowly, it can take months, after which a solid layer of dust will collect on the surface. Therefore, drying oil is most often used to impregnate wood – a pre-thickened oil, there are several dozen ways to prepare it. The last stage of the most powerful polymerization occurs directly on the surface of the product in contact with oxygen and under the influence of ultraviolet radiation. In such conditions, drying oil is able to harden within several days..

Natural drying oil

The key difference between oils of petroleum origin (mineral) is the participation in the polymerization of a huge amount of various hydrocarbon compounds. Special compositions for carpentry processing undergo a long multi-stage preparation, and therefore the price tag for them is transcendental. Therefore, there is no and cannot be a guarantee that ordinary transformer or compressor oil will polymerize properly, and the surface texture will retain its naturalness. It’s not even worth talking about working off: it is suitable exclusively for impregnation for protective purposes and only on the condition that direct contact with the processed product is excluded. So in the future, under the impregnation with oil, we will always mean the treatment with natural drying oil, sometimes with special additives, which for simplicity and beauty of the syllable will occasionally be called oil.

Mineral oil for wood products

Used types of additives

The polymer film, into which the drying oil is converted, has the only exceptional property – hydrophobicity. At the same time, it qualitatively prevents water from seeping into the fibers in the liquid aggregate phase, although gas exchange, including water vapor, is partially preserved – the tree does not lose its natural ability to “breathe”.

It is possible to achieve more outstanding properties of protective impregnation with the use of certain additives. It should be understood, however, that purchased special oil already has a number of properties that are described in the annotation; a change in the proportions of the components that make up the composition can make the drying oil behavior unpredictable. Therefore, it is advisable to experiment with additives only in the process of self-preparation of oils..

The additives can be divided into four groups according to their action:

1. Increasing the hardness and strength of the polymer film. This is usually achieved by mixing oils of different breeds, i.e. increasing the variety of reagents, but additives in the form of natural wax can also be used..
2. Antiseptic. Such additives help to avoid preliminary impregnation with bioprotective compounds, which not only improves oil absorption, but also favorably affects the timing of work. As antiseptics, both chemical reagents (bromides, fluorides) and natural substances, for example, bee propolis, can be used..
3. Accelerating polymerization. Interior surfaces do not experience harsh solar ultraviolet radiation and are limited in contact with oxygen, and therefore harden very slowly. The process can be accelerated by introducing metal salts (desiccants) into the drying oil, but the increased content of heavy metal compounds does not always fit into the building ecology norms.
4. Changing decorative properties. Ordinary drying oil practically does not change the color of the tree, but it tints it qualitatively. By adding colors and finely dispersed pigments, you can give the coating a completely different color: from dark chestnut to whitish or lemon.

Oil application and curing

It was the turn of the development of the nuances of the technology of work in wood stabilization. The first step, oiling the wood, is often described as a conventional wetting. It is assumed that the most important thing during application is the movement of the brush or tampon strictly along the fibers, but there are actually much more subtleties. First of all, this concerns the preparation of a wooden product: its joinery must be completely finished, and the surface must be carefully sanded with abrasive paper with a grain size of at least 300-360 grit. Naturally, the moisture content of the wood at the time of impregnation should be minimal, in the region of 12-14%.

The most important factor in high-quality oil impregnation is the application of strictly the same amount of oil to each unit of surface area at a time and the same holding time in all areas. These two points are of key importance: a different amount of varnish applied will lead to the appearance of a difference in color, and uneven application – to the appearance of streaks and dark spots, which are almost impossible to remove later..

The method of application should be chosen commensurate with the area to be treated. For small items, a brush made of natural bristles or a tampon is well suited, for floorboards – a roller with a velor or fur coat. For oiling the walls of a log house, it is preferable to use airless spray units with a torch width of 0.5 m or more. In most cases, excess oil must be removed after the coated surface ceases to be greasy and begins to stick slightly to the fingers. The exposure time for different formulations varies greatly and you need to focus on it, choosing the area of ​​the site to which the oil is applied in one step. It is necessary to proceed from the calculation that the duration of the drying oil application was 10-15 minutes less than the holding time.

As for movement along or across the fibers, there is no fundamental difference. There is no mechanical effect on the tree, in order to lift up soft fibers, you need to try very hard. But it should be remembered that due to moisture on the wood, fine pile will inevitably rise, which subsequently must be removed by light grinding. And one more caveat: on the ends of the products, oil is absorbed much faster, nevertheless, it must be applied in the same quantities as on the longitudinal sections of the fibers..

Rubbing impregnation

The oil should be applied not too much, but not too thinly. Finding a middle ground is key, otherwise the perfect showdown quality cannot be achieved. The bottom line here is that while a film seizes on the outer layer of oil, the composition inside is limited from contact with oxygen and continues to be intensively absorbed. However, the absorption capacity differs not only in individual breeds, but even in different areas of the workpiece. In order to eventually lay down the oil evenly, the excess should be removed before they finally polymerize..

Rubbing the oil can be avoided when treating surfaces that do not have high aesthetic requirements. This is usually done with roughly processed wood: log walls, ceiling beams and others like them. At the same time, it is necessary to apply oil with a reduction in consumption by 20-30% compared to surfaces that will subsequently be wiped off.

It is ideal to rub the oil with cellulose wipes or cotton cloth, which does not leave fine cellulose fibers. Unlike the application process, the direction of the fibers must be strictly observed when rubbing. At the same time, you need to rub oil not just along the fibers, but against the direction of their growth, achieving a thorough blockage of blood vessels.

It was mentioned above that the time for rubbing should be determined with a margin of 10-15 minutes. This is done in order to first walk over the entire surface and carefully rub the excess into the pores, and then wipe the entire surface several more times, increasing the range of motion. Friction forces play an important role in grinding the oil, due to which the composition is heated, as well as intensive stirring to activate oxidation. Thus, there is every chance to achieve the formation of a polymer film with a uniform thickness over the entire surface of the product. Oiled rags should be disposed of immediately after use or stored in a metal box outside before disposal..

Multi-layer application and combination of oils

Conifers have a high resin content and therefore their oil treatment is usually carried out in only one, maximum – in two stages, after which oil absorption becomes practically zero. But the impregnation of deciduous valuable species can stretch for two or three, or even five layers. The logic here is simple: you need to achieve a surface state in which absorption stops almost completely, otherwise the tree does not acquire the proper hydrophobicity. This is especially important when working with large-vascular wood: alder, oak, elm.

For the most part, multi-layer oil application is a repetition of the same operations. However, there are some tricks, for example, using compositions with different ratios of drying oil and additives in different layers. For the first application, an almost pure liquid drying oil is used, possibly with a small addition of an antiseptic or color, which acts as a UV filter. Sometimes it makes sense to increase the intensity of absorption by introducing 15–20% turpentine into the oil. As you move to the final layer, wax or resin is added to the heated oil, increasing the holding time and reducing consumption. Naturally, this practice requires skill: it is very important to adapt to the behavior of the tree when it comes into contact with oil, by trying out the chosen application technique on scraps of the same material..

In the process of wetting the wood, as already mentioned, the pile rises. Its removal is an obligatory component of multilayer application: in parallel with grinding, the hardened polymer film is removed, access to uncorked vessels is opened, due to which a deeper and higher-quality impregnation occurs. It is recommended not to grind the last one or two layers, but to polish with felt or cloth with a small addition of cold ground wax to the surface.

Oiled wood care

In use, oiled wood is one of the most problem-free materials. The coating practically does not tarnish, does not chip or crack, as is often the case with varnish and paint. But there are also disadvantages: such a tree is less resistant to damage, although it is enough to simply eliminate them, at least visually, it is enough to re-soak the dent or chip.

Oil-impregnated wood requires renewal of the coating at intervals from 2 to 5 years. The term depends both on the structure of the tree and the type of oil, and on the operating conditions. For example, in outdoor conditions, constant contact with water and sunlight leads to depletion of the protective film. Reapplication is no different from the initial one, but the surface must be cleaned with fine emery paper to remove residual oil, dust and dirt, while impregnation should be carried out immediately after cleaning.