Outdoor wood has two main enemies: UV (ultraviolet rays from sunlight) and humidity. The first causes a kind of superficial burn – like on our skin, resulting in small cracks and greying. Nothing dramatic, the damage is mainly aesthetic, and the wood is not affected in depth.
Moisture poses much more severe problems: if rainwater does not run off or does not evaporate quickly, if the wood remains in contact with the ground or if the moisture can rise by capillary action, the moisture content of the wood will allow the installation of lignivorous fungi that are precursors to rot and favor attacks by wood-eating insects. Can chemical preservative treatments be avoided?
Durable Species, without Sapwood
Some naturally durable species from our regions can be used without treatment when the wood is laid vertically (risk class 3) and allows good water drainage (cladding, windows, shutters): in particular Douglas, larch, chestnut, oak, and locust. Only the last three species are recommended when the wood is laid horizontally (balcony or terrace boards) or in contact with the ground (risk class 4). These woods must also be selected and cut in such a way as to eliminate the sapwood, the peripheral part of the trunk rich in sugars, which attracts wood-eating insects.
What Are the Advantages of Protecting Your Wood?
Embellishes and Protects
Beyond maintaining the aesthetic aspect over time, using a wood oil or a saturator in the protection of wood will revive its original color and enhance the grain of the wood while maintaining its natural appearance.
Stabilizes the Wood
Oiling a wood allows improving its dimensional stability durably, thus reducing the phenomena of deformation (tiling, swelling, and shrinkage), cracking, or surface splitting.
Natural and Ecological
Choosing an “Oleobois” protective oil means choosing a healthy and environmentally friendly solution; the composition excludes fungicides, turpentine, and any petroleum derivatives frequently used (paraffin, white spirit, …).
Easy and Economical Maintenance
Maintenance is easy because once oiled; wood does not need to be stripped or sanded before renovation: a cleaning with black soap followed by a simple re-oiled surface is enough.
Greying of The Wood
What Is Wood Graying?
Wood is a material nearly made up of polysaccharides (cellulose and hemicelluloses) and lignins that will be degraded under ultraviolet photons’ action. This photodegradation of the lignins, which is also accentuated in the presence of water, is responsible for the evolution of the color of the wood. Greying is observed on the timber used outdoors without any physical protection and UV protection. This phenomenon causes a change in the original color of the raw wood over time, which tends to become gray.
What Are the Consequences of Greying?
Greying or graying, which is a very superficial phenomenon, only affects the wooden structure’s aesthetics. It does not indicate a structural alteration and does not affect the solidity of the material. The appearance of this phenomenon is limited to the surface of the wood. The loss of structural durability (which can go as far as the ruin of the material) is, for its part, due to attacks of biological origin that affect the wood in its mass.
Is it possible to avoid the greying of the wood without maintaining it?
NO – Without finishing products and without maintenance, it would be illusory to claim to be able to prevent the wood from greying.
Will the application of a finish prevent the wood from turning gray?
YES – If this application is made regularly, it is possible to avoid this phenomenon. The hydrophobic nature of the oil strongly limits the wood’s affinity for water and therefore delays its action.
Rectified and Thermo-Oiled Wood
Several recent processes have made it possible to improve the durability and dimensional stability of other species significantly: these are high-temperature heat treatments (210 to 250°C) in several phases, carried out in special furnaces, either under an inert atmosphere with nitrogen (rectified wood) or with water vapor injections (Finnish heat-treated lumber). The wood takes on a beautiful brown color and becomes hydrophobic and very resistant to fungal or insect attacks. However, the high temperature weakens these woods a little, which cannot be used for structural purposes (mainly in siding, parquet, and terrace boards).
The so-called homeothermic process does not have this disadvantage: the wood is only heated up to 130°C, with an immersion in a mixture based on linseed oil and vegetable oil derivatives, which allows a deep impregnation. This also ensures a longer resistance to greying and does not require regular maintenance. The process creators have started to market it in France: three manufacturers in the wood industry have already bought it, and others are in the pipeline. The recent Wood-Protect process patented by Lapeyre and INRA-INPT in Toulouse is of the same type, with impregnation by autoclave and then by soaking at 140°C in a mixture of vegetable oil derivatives and acetic acid.
High-temperature treatments make the wood wholly waterproof and fungus resistant.
The wood is brought to a temperature between 210 °C and 250 °C in special ovens. It then changes color to become darker. The main disadvantage is that it loses its strength. It can then only be used for cladding or flooring.
Oleothermy is a treatment that consists of 3 phases: heating to 130°C in a rapeseed oil bath, cooling in a linseed oil bath, and drying. Since the heating temperature is lower than the previous method, the wood is less brittle.
Studies have shown that homeothermic heating is beneficial when done after boron treatment. Boron has anti-inflammatory properties. The problem is that it is not resistant to washing. Thus, the homeothermic makes it possible to fix the molecule and make the wood more resistant to flames, water, and shocks. To learn more about this method, here is a doctoral thesis that was done on the subject.
Oils, Stains, and Paints
The durability of certain species such as oak and chestnut is mainly due to their high tannin content. However, these are gradually washed out by rainwater, which is slightly acidic. Like other species, oak and chestnut, therefore, require surface protection. Linseed oil with a little turpentine added – to be used in hot weather (it penetrates better) – is classic and inexpensive protection, water-repellent, and delays greying.
Organic wood stains, which are colored but show the wood grain, provide better protection against UV rays thanks to the pigments they contain. However, they should be renewed every 3 to 5 years for the south facades and every 8 to 10 years for the north facades. Unlike paints, they do not require sanding before renewal (a brush stroke is enough to remove the pigment dust). As for organic lacquer paints, they provide more durable protection since they contain fillers (especially chalk) that form an entire screen against UV rays. It’s a bit like sun creams; the security depends on the screen’s quality and the exposure.
To improve the durability of outdoor wood naturally, opt for a stain, for example, a mixture of linseed oil and turpentine. Some commercially available wood stains are colored and provide slight UV protection. The advantage of this method is that no sanding is required.
For even better protection, apply organic lacquer paint. It will provide optimal protection against ultraviolet rays—favor microporous paints containing chalk fillers to let the wood breathe.
Protecting exterior wood naturally can be done with a protective stain or heat treatment. The choice of method depends on the characteristics that you wish to modify. If certain wood species can be used without protection, they must be stained after a certain period because the protective tannins will have disappeared. If you do not do this, you will have to have a professional moisture treatment.
Protecting Wood from Water
Protecting wood from water is an essential function of an exterior finish before any decorative aspect. It is recommended to save the material with paint, varnish, stain, saturator, or oil. Indeed, it is essential to achieve a real barrier effect, which must be waterproof if the wood is not to deteriorate too quickly.
This makes it possible to preserve natural, solid, raw, or veneered wood virtually over time. It is protected to keep for many years in the face of the various climatic aggressions encountered. It is durably preserved from humidity, rain, bad weather, light, sun, and ultraviolet rays, making it age prematurely.
Remain Naturally Permeable to Moisture
Remain moisture permeableStaying naturally permeable to smoke is very important. Wood is made up of plant fibers that have an excellent affinity with water. It is, therefore, a fragile material that remains easily permeable to water. It remains particularly sensitive to various liquids that penetrate it.
Wood absorbs very quickly the humidity that is present in the ambient atmosphere. It soaks up water before naturally releasing it because it is a hygroscopic material. It remains in constant equilibrium with its environment, whatever the moisture content.
These different humidity variations are at the origin of the usual dimensional transformations of wood. They have the effect of causing deformations that can sometimes be significant. It works by swelling if the air is too humid. It shrinks when the atmosphere becomes drier.
Rain, showers, thunderstorms, and other bad weather that are in contact with the wood can cause the appearance of unsightly stains, streaks, drips, and halos. Moisture, infiltration, condensation, and water vapor are also responsible for the premature aging of wood over the years.
Do Not Prevent Exchanges with The Outside World.
Do not prevent exchanges with the outside not prevent interactions with the outside; it must be respected. When you want to protect the wood, a water-repellent product must be applied to avoid water from penetrating it. It must be ensured that it is not impregnated by moisture if it is to last over the long term.
A wood treatment product can only be perfectly suitable if it respects the different moisture exchanges. The wood must be able to continue to regulate itself with its environment. It is essential to ensure that the film remains sufficiently micro-porous to guarantee a good exchange efficiency.
On the other hand, impermeability and water tightness should not be confused, which are very different notions. Waterproofing must be prohibited in the case of wood protection. Making a wood completely watertight may cause the material to rot in the long term.
Gas exchange, which regulates the moisture content in the wood’s pores, must never be prevented. A wood paint must allow the substrate to breathe without ever stopping the internal evacuation to the outside. It must just prevent water from penetrating the heart of the wood, not to alter or deteriorate it.
Choosing a Right Wood Treatment Product
Choosing a wood treatment selecting the right wood treatment product is essential to protect wood effectively over time. There are different types of products that are capable of effectively preserving this material. One can use a product that penetrates deeply, such as oil, impregnation, or saturator.
A penetrating treatment provides more effective protection than a product that deposits a film on the surface, such as paint, varnish, or sealer, for example. Indeed, while a film-forming product may seem useful initially, this is not always the case in the long term.
Indeed, they can end up cracking, flaking, cracking, or peeling off over the years. Infiltration, water, or humidity penetrates the material, which becomes poorly insulated. It is then essential to sand or strip the surface of the wood to bare it again to be preserved.
Silicones are widely used in wood waterproofing products. These harmful substances should be avoided in the same way as petroleum solvents, which are still present in many products. They are not harmless to the user, the environment, or nature. It is better to select a bio-sourced product of plant origin that is consistent with this natural material.
Maintain Regularly for Adequate Protection.
Maintain for good protection maintain regularly for an adequate defense, remains an operation that should not be forgotten to perform. Regardless of the type of waterproofing chosen to preserve the wood, it is necessary to maintain it regularly so that the protection remains sufficiently effective over time.
Tedious preparation, sanding, gritting, or stripping of the surface can be avoided using an oil, saturator, or impregnation. They have the particularity of protecting the material throughout its mass without creating a film on the surface that can flake off afterward.
A waterproofing agent’s function is to protect the wood from stains, marks, rings, and everyday wear and tear. It is generally associated with an anti UV agent that will prevent the wood from becoming too grey in the long run. It thus limits the phenomenon of swelling or shrinkage.
A non-film-forming water repellent has many advantages for preserving a wooden surface. It is very effective against bad weather thanks to a barrier effect. Also, it remains very effective in nourishing the wood in all its depth to the material’s very heart. It also protects the support from light, sun, and ultraviolet rays.