In recent years, much attention has been given to timber constructions. Being a sustainable and renewable material, which captures a huge amount of carbon during its growth, the innovations related to this material have allowed for increasingly higher constructions. However, when we talk about wood we approach an immense variety of species, with different strengths, nuances, potentials, limitations and recommended uses. While there are extremely hard and heavy woods, with strengths comparable to concrete, there are other soft and soft woods that are suitable for other purposes.
In any case, being a natural material, wood is porous and adapts to the temperature and humidity conditions of the environment in which it is inserted, being able to absorb everything that enters, such as oils, dirt, and chemicals. Without a proper finish, the wood can dry, crack, lose its natural tone and deteriorate. If you are exposed to sudden changes, such as periods of high humidity and drought, you may end up swelling or rotting.
Although we are aware that maintenance is vital for the proper functioning of all types of buildings, when it comes to wood, this is even more essential. A suitable finish prevents the wood from deteriorating rapidly, increasing its useful life and exhibiting its natural characteristics. Availability and terms used for each type of finish may vary by country. Below, we have compiled the most used finishes today, presenting their main characteristics and uses:
Varnishes
Wrongly, the word varnish is often used for a wide range of wood finishes. The varnishes create a transparent layer, like a film on the applied surface, which covers the pores of the wood, highlighting its veins and its natural colors. It is a product based on drying oils and synthetic resins. There are several types on the market, such as marine varnish and polyurethane, which are very resistant to water and moisture. There are varnishes with protection against ultraviolet rays, very useful for outdoor structures. Other types allow changing the tone of the wood through dyes.
Varnishes are quite versatile and are widely used in facades, structures, frames, and internal parts. When the varnish layer begins to peel off the wood, leaving it unprotected, the piece must be sanded and varnished again.
Impregnants
Impregnants works slightly differently. Unlike varnish, they penetrate the wood and leave their pores open, nourishing their fibers and allowing the wood to "breathe". This gives a more natural look to their veins, especially to the touch, but even in its most transparent version, it ends up obscuring the piece a bit. Because it permeates the wood, it is a finish that makes it extremely water-resistant. Easy to apply and maintain, Stain does not come off, since it is absorbed by the wood and does not form a layer of a protective film.
Its uses are similar to varnishes and are also widely used in roofs.
Oils
Oil finishes are very popular among carpenters, as they tend to highlight the character of the wood very well, without changing both its color and texture. Made of natural products, they are quite easy to apply and maintain. They accompany the natural movement of the wood, hydrating and waterproofing it. On the other hand, it is not a finish as resistant to the weather as the previous ones, needing to be applied periodically. Although the most common oils are Linseed and tung oils, there is the possibility of using 'raw' or polymerized oil, which undergoes a heat treatment to make it more resistant to time and accelerate drying time.
In general, oils are used mostly in areas with low exposure to sun and rain, but they can also be used to protect cooking utensils, such as tables and spoons, for example. In these cases, it is recommended to use mineral oils.
Shellac
Shellac is a natural finish secreted by the Kerria lacca insect, a type of beetle found in the forests of India and Thailand. As a varnish, shellac dries quickly, forming a hard, strong and flexible film, which is useful for varnishing floors and furniture. It is used infrequently today because it is not very resistant to water or alcohol. It is usually purchased in small pieces that are diluted with alcohol before use.
Even so, there are carpenters who use shellac to finish fine furniture.
Waxes
Marketed in liquid, paste or solid form, waxes are derived from a variety of mineral, vegetable and animal sources. The most common are bee and carnaúba. As a finish, the waxes do not penetrate the wood, but remain on it, preventing oxidation. Wax, therefore, if used alone, has little effect on wood protection. The interesting thing is that it can be applied to parts that have already received the application of oils, giving the surface a soft shine and a pleasant sensation. It should be used in areas that are not exposed to weather.
It is important to note that when addressing the possibilities of wood finishes, several issues need to be considered, especially the future use of the piece, where it will be installed and its expected life. And that includes considering, at times, not using any product for finishing. This is because there are species of noble woods, heavy and hard, such as Cumaru (Dipteryx Odorata), whose resin itself creates a natural protection. In the Vila Taguaí project, by architect Cristina Xavier, no product was applied to the wood. There are also construction methods, such as acetylated wood, which does not require the application of finishes and, even so, has a long useful life. Likewise, a finish for panels on a CLT slab will be different from that of a park bench or that of a piece of furniture for an indoor environment. The important thing is that the architect, when specifying, has knowledge of the possibilities of the species and the function of the piece, in order to find the most appropriate solution for each situation.
Editor's Note: This article was originally published on February 25, 2020.
