- Wood oil – differences and classification
- Differences in viscosity
- Decorative properties of oils
- Difference in solids and wax content
- Protective properties of oils
- Selection according to the type of wood
- Features of the application and maintenance of oil finishing
Oil impregnation is one of the simplest and at the same time effective ways of protective and decorative wood treatment. Today we will talk about the types of oils, differences in compositions for indoor and outdoor use, as well as the technique for impregnating wooden surfaces and wood products.
Wood oil – differences and classification
Coating joinery with oil can literally be called the most environmentally friendly and safe way of wood processing. This is because the composition of oils contains either absolutely natural or inert chemical compounds. Let’s make a small reservation right away: there are oils for wood, which include volatile solvents, but after drying, such a coating remains absolutely harmless.
Almost all oils for wood are made on the basis of linseed oil, or more precisely – linseed oil or other natural drying oil. A characteristic feature of this material is its extremely high polymerization tendency. Pure wood processing oil is almost never used. The drying oil base can also be hemp, tung or other origin, mainly the differences are expressed in conditions that promote thickening and polymerization.
Oils differ greatly in their technical characteristics: viscosity, density, type and content of solids, volatile solvents and special additives. All this not only affects the performance of the coating, but also completely determines the application technique and the nature of interaction with a certain type of wood. On the other hand, oils are also classified according to their decorative effect, that is, according to such characteristics as the intensity of the appearance of the texture and the depth of the change in the color of wood..
Differences in viscosity
In joinery there are about two dozen common wood species, differing in density, porosity and vessel sizes. In each case, the oil must be selected individually, taking into account also the size, shape and specific features of the processed product. Please note that it is possible to adjust the viscosity with solvents only when working with tung oil, other formulations absolutely do not tolerate this.
The thicker and more viscous the oil is used, the more difficult it is to apply an even coat before polymerization begins. Working with thick oils requires more care, the resulting drips are subsequently very problematic to remove. Advantages of thick oils – high drying speed, comparable to some types of varnishes. Also, due to the high content of solid particles, such oils form a stronger film, providing protection from both mechanical damage and contamination..
Thinner oils are used to treat products that either have significant surface area or are replete with small parts with many hard to reach places. Low viscosity oils can be applied for a long time without the fear of uneven drying. However, in order to obtain high-quality protection, the product must dry for a long time, moreover, the application of such oils is usually performed in 3 or more layers..
Decorative properties of oils
When choosing an oil, the visual effect of its application is of paramount importance. From this point of view, oils are divided into conditionally colorless and tint. Why are oils called colorless only conditionally? Because in any case, they change the color of the wood surface, but at the same time retain transparency. Coloring oils include a colloidal suspension of a coloring pigment – from white to carbon black, which somewhat muffles the contrast of the texture pattern.
Transparent oils always show wood texture in different ways. This is due, first of all, to the viscosity index. The lower it is, the finer pores of wood can be impregnated. Thick oils show only the general grain pattern, while thinner oils show fine texture details. So, for the treatment of oak surfaces, the oil should have a slightly below average viscosity, while for alder, saturated thick compositions are recommended.
The use of coloring oils is much like staining. Oil tinting of wood is rarely used as an independent treatment. Much more often, with the help of such compositions, they emphasize the soft veins between the hard fibers of the tree or cover individual elements of furniture. After drying, the tinting oil has a lower glossiness than colorless.
It is not known whether such a property of oils as smell can be attributed to the decorative qualities. In fact, all oils smell completely different, from hay making to roasted seeds. After drying, the smell from oil processing turns into a very persistent, but subtle aroma, which can become a valuable part of the interior color.
Difference in solids and wax content
Despite the apparent homogeneity, wood oils are a colloidal system consisting of a liquid oil base and a suspension of solids. The latter are products of partial polymerization of the oil, special additives (desiccants in oils for external use), resins and natural wax. You are absolutely right if you assumed that the viscosity and density of the oil increases with the content of solid particles..
The high content of partially polymerized inclusions in the oil helps to eliminate the effect of raising the pile when the wood is wetted. By using saturated, thick oils, intermediate sanding or polishing is sometimes completely avoided. This is an interesting trend: thick oils are ideal for large-vascular wood, where the formation of high pile is possible, while flowing compounds are best used for dense, hard rocks that are practically not prone to “shaggy”. On the other hand, the drying time of the oil is controlled by the solids content..
Inclusion in the composition of the dissolved wax has a slightly different purpose. The wax helps to seal the pores of the wood tightly, providing it with excellent hydrophobicity. Such waxing is used mainly in outdoor decoration to protect wood from getting wet and dust accumulation in small pores. Another reason is that wax is added to the oil by being dissolved in turpentine or some other volatile solvent. This raises the problem of persistent unpleasant odor, which is highly undesirable in living rooms. But there are oils in which the wax dissolves when heated. These mixtures are unstable and wax often precipitates, making the oil more difficult to apply. However, due to the high environmental friendliness of such a composition, it is possible to wax the interior parts, but not for the purpose of protection, but to give a light shade and glossy shine..
Protective properties of oils
Unlike most wood preservatives, the oil does not form a dull film, maintaining the vapor permeability of the material. At the same time, the hydrophobicity of the surface increases several times – upon contact with liquid water, the absorption of the tree is practically zero. Nevertheless, the product made of wood remains susceptible to shrinkage and swelling; oil coating does not relieve these phenomena.
The protective effect of the oil consists in the compaction of the outer layers of the tree, due to which the penetration of pests inside the array is excluded. Due to the absence of paths for moisture penetration, the tree becomes the least susceptible to organic damage by mold, fungus or blue.
The oil also retains the color of the wood well, especially for the exterior of the house. A crust of oil on the surface effectively scatters sunlight and restricts oxygen flow. Due to this, the rate of cellulose oxidation and the associated appearance of a grayish bloom are significantly reduced..
All these properties are more pronounced, the thicker the oil is used for coating and the more layers are applied. Oils are characterized by separation of protection into two barriers: internal, achieved by impregnating the pores, and external, formed when a thin oil film dries on the surface. Remember that oiled wood has a higher thermal conductivity than dry wood..
Selection according to the type of wood
Wood oil is always selected for a specific species. It is recommended that you carry a trial cut of wood of the same type and quality of processing as is typical for wood trim. Trial application, even on small areas, will help to quickly assess the behavior of the composition in contact with wood, as well as the decorative effect.
To begin with, all conifers practically do not need oil impregnation. If absolutely necessary, you should use thick formulations applied in one layer. This is due to the presence of a large amount of resin in the pores, due to which the tree loses its ability to absorb even flowing oils. Therefore, it is required to achieve rapid drying of the oil on the surface and in the surface layer..
Thick saturated oils are also used in the processing of low-density wood (linden, alder), especially fruit species with the most developed vascular system. There are no obstacles for impregnation with thick oil, while excessively fluid compounds penetrate too deeply and will forever remain in a liquid state, deprived of oxygen.
The exact opposite approach is used when processing beech, birch or sycamore. Due to the high density of such wood, they are impregnated either with unheated oil or with compounds containing a solvent. Often, when working with hard dense breeds, their processing is performed in combination: first with oils that penetrate well into the wood, and then – with thick compositions with a high proportion of dry residue and wax.
Features of the application and maintenance of oil finishing
The process of applying the oil itself is extremely simple, it is enough to follow the instructions for using a certain composition. But there are general rules:
- Before applying oil, wood must undergo chamber drying (moisture content no more than 12-14%) and surface grinding until tactile roughness is eliminated.
- Application is carried out strictly in layers over the entire surface of the product, each layer must be completely dry.
- After a specified period of time after application, the excess oil is rubbed with a dry cloth, distributing it between areas with uneven absorption..
- Oil is applied to all sides of the part in equal amounts, and surfaces with an open cut of fibers are no exception, despite the increased absorption rate.
- If, after the oil dries, a pile has risen on the surface, before applying the next layer, it is imperative to carry out preliminary grinding, otherwise, when rubbing the oil film, fibers from rags will also settle on the surface.
Oil impregnation retains performance for 4-5 years indoors and 2-3 years outdoors. After these periods, the coating is renewed, for which it is enough just to thoroughly clean the surfaces and apply another layer of oil. The thickness of the oil is chosen depending on the degree of damage to the previous finish, usually these are fairly thick restorative compositions.