Finishing of wood surfaces
Wood is a natural product – there are an estimated 25,000 types of wood, of which 600-800 are of commercial significance, and they are all different from each other. As a material, wood undergoes a natural aging process. If it is exposed to the elements it weathers or acquires a natural patina. Old larch wood facades, which may have survived for hundreds of years, are an example of this. But even if it is protected from water and from UV rays in direct sunlight, wood undergoes permanent changes, such as shrinkage and warping due to loss of water or, in some species, changes in colour due to reactions with the oxygen in the air.
A variety of methods of protecting processed wood have been developed. Lacquers do this by sealing the wood completely with a tightly closed film of lacquer. This blocks any exchange of moisture with the environment. Classic lacquers contain natural resins such as shellac or copal as a film forming agent, while modern lacquers contain predominantly synthetic resins. The damaging effect of ultra violet radiation is also significantly reduced by these lacquer resins and by the UV-absorbent substances that are often added to the lacquer. The Wood Protection Sealing Varnish (item no. 70 032.98) we offer contains highly abrasion-resistant synthetic lacquer resins that produce an extremely resilient surface. Our Basket and Wicker Varnish (item no. 69 896.97) produces a high-strength but flexible film.
The most natural way of protecting wood is by oiling it with drying oils – these contain a high proportion of what is known as double bonds, which can react with the oxygen in the atmosphere, in the process cross-linking and forming a film that can vary from tough elastic to hard. In the food sector, when referring to oils with a high proportion of double bonds, the term polyunsaturated fatty acids, or oils, is often used. All drying oils contain a high proportion of polyunsaturated fatty acids. Undoubtedly the best known, and cheapest, drying oil is linseed oil; however, this has an odour that many people find unpleasant when they are working with it. There is also a whole range of different vegetable drying oils, some of which are almost odourless. With no other additives drying oils only harden very slowly, taking several weeks to do so. To make practical use of these oils, drying accelerators (siccatives) are added to them; this reduces drying times to a few hours or days. While in the past toxic lead compounds were often added, nowadays cobalt and/or manganese siccatives are widely used. But even these heavy metals can be harmful to the health, and should not be used, at any rate for wooden products that come into contact with food, or for wooden toys. Oiled woods do not have a closed surface film but, when the oil is applied correctly, it soaks into the wood, forms a protective film on the fibres of the wood, and hardens on the inside of the wood. Oiling brings out the natural grain and beauty of most woods, while at the same time making the wood both water and dirt-repellent. Drops of water roll off wooden surfaces that are oiled in this way. Unlike lacquered wood surfaces, the pores of oiled wood remain open, so if they are exposed to water over a long period it is slowly absorbed by capillary force. For this reason, any liquids that are spilled on it should be wiped off as quickly as possible; this applies particularly to liquids that stain noticeably, such as red wine. The water-repellent effect of the layer of oil decreases over time, so oiled wood must be maintained regularly, depending on the degree of use to which it is subjected. As soon as water stops rolling off, the wooden object should simply be treated again with a small amount of oil. If any visible damage appears on oiled wood surfaces during the course of use these can, unlike with lacquered pieces, also generally be removed by sanding down and applying more oil. Any colour difference on objects that have only been partially sanded, caused by the surface of the wood having darkened in the light and then being restored to its natural colour by sanding, will, with most woods with which we are familiar, even out over the course of a few months.
Our Natural Wood Oil (item no. 73 003) is a very high-quality product based on totally odourless modified plant oil. This oil is also free from harmful cobalt, manganese or even lead compounds, and is therefore also suitable for wooden toys.
By applying wood waxes it is possible to produce an even more refined surface with its own unique feel. There are, unfortunately, many different products available, and their exact applications are not always clearly defined. What we mean is high-quality vegetable waxes that are applied as a final layer to wooden surfaces that have already been treated with oil. Our Natural Wood Wax (item no. 73 053) is based on Natural Wood Oil, which acts as a carrier for hard wax. The oil is completely absorbed into the wood, leaving a wafer-thin, hard wax film on the surface: this can then be polished to an elegant, silky shine. Wood surface treated in this manner are well protected and pleasant to the touch, which makes them ideal for decorative objects in particular.
Oiled surfaces are the best choice for everyday objects, as they are easier to repair and to maintain. Waxed surfaces are unsuitable for contact with hot objects such as saucepans or cups, because these will melt the wax. Oiled surfaces are also better than waxed ones where there is going to be frequent contact with water since, if the layer of wax is damaged, any water that penetrates will spread out under the wax film, which can cause unsightly dull spots. Waxed wood can, of course, also be sanded down again and refreshed but, unlike with oiled woods, it is only possible to make limited partial repairs.
When wood is to be oiled it should normally be sanded smooth, to approximately 240 grit. It is, of course, possible to sand it even finer. Remove all sanding dust thoroughly! Then apply the oil generously, preferably with a brush that does not shed hairs or a lint-free cloth, then it is recommended to rub it in vigorously for a few minutes in the direction of the grain. On patches where the oil is absorbed relatively quickly, apply a little more oil. Cross grain wood in particular can absorb enormous quantities of oil. After it has been allowed to soak in for around 30 minutes, any excess oil should be completely (!) removed. No shiny patches should now be visible. To do a good job, use a few absorbent cellulose cloths and then a lint-free cloth, applying a bit of pressure and always working in the direction of the grain. The layer of oil must now be left to harden for at least 12 hours; leaving it to dry for longer will do no harm. If desired, depending on the quality of surface required, carry out an intermediate sanding with a fine grit, between 320 and 400, without applying too much pressure. Remove all sanding dust thoroughly! When the second layer of oil is applied, the wood will absorb significantly less oil, although a few highly absorbent spots may once again require a little extra oil. It is once again important to remove any excess oil completely after it has been allowed to soak in for 30 minutes, and then to leave the oil to harden for at least 12 hours.
Two to three coats should be sufficient for most woods, but the process of oiling, drying, and sanding if necessary, can be repeated as often as you like, until the surfaces are really saturated. If you are working with extremely absorbent woods, we recommend using Shellac Primer before you apply the oil; the primer will soak deep into the wood, which means you will need a smaller quantity of relatively expensive oil.
For a waxed surface, simply apply Natural Wood Wax instead of Natural Wood Oil for the second or final coat. Remove the excess and then leave the wood to dry for at least 12 hours before polishing the thin, almost invisible film of wax on the surface with a lint-free cloth, pressing down hard, and always in the direction of the grain.
Problems with treatment: if excess oil is not completely removed, or if you try to remove it after the wood has been left to dry for more than 30 minutes, or if surfaces are very rough, making them difficult to clean, the oil may harden on the surface and form a film. This film may still feel sticky even after a long time. In these cases, the surface can first be cleaned with balsam turpentine or with turpentine substitute (white spirit), and the surface can be sanded down with a fine-grit sandpaper. Afterwards simply apply a further thin coat of oil and process according to the instructions.
Consumption depends heavily on the type of wood and the direction in which the wood was cut from the trunk of the tree, but at least 20 g per m² to around 150 g per m² should be reckoned with. The more fibres that have been cut crossways, the more oil the wood will absorb. Oak is very dense and only absorbs a little oil, while beech is a highly absorbent wood and requires a lot of oil. For this reason, it is not easy to give an accurate general estimate of requirements. The best thing to do is to carry out a preliminary test on scrap pieces of wood. If the wood absorbs a lot of oil, applying a coat of Shellac Primer will reduce the quantity of expensive oil required.
Clean tools with balsam turpentine or turpentine substitute (white spirit).
WARNING! Fire hazard – do not leave oily cloths unattended. Seal in an airtight container for disposal.
Fibrous materials can have a very large surface area; for example, cellulose fibres in paper towels or textile fibres in cloths. A small cloth may actually be made up of thousands of individual fibres and, when the individual fibres are added together, their total surface area can be many square metres. When oils are drying on the cloth, they react with the oxygen in the atmosphere. Although an oiled table top does not noticeably heat up while it is drying, a crumpled, oil-smeared cloth can get hot enough to self-combust! For this reason, all paper and fabric cloths that have come into contact with oil should be spread out to dry in the open air at a sufficient distance from inflammable materials, or else dampened with water and disposed of in an airtight container. Metal cans, preserving jars or tightly knotted, non-perforated plastic bags are suitable for use as airtight containers.
