What is varnish? It is a type of product or finish used mainly to protect and beautify wood, although it can also be used in other materials such as metals, clay, concrete, natural stone, etc.
It consists of mixing or dissolving resinous substances in a solvent (which can even be water) that is applied on a surface, leaving a protective layer.
Types of wood varnish according to composition
Not all projects have the same needs and it is convenient to know how to choose the best varnish for each job. Here we explain the properties and main uses of each type of varnish.
Polyurethane varnish for wood
This type of varnish is obtained by mixing polyurethane resins with other fillers. Polyurethane is a very versatile plastic polymer, used in several sectors: insulation, clothing, coatings, adhesives, mattresses …
Characteristics: In the specific case of polyurethane varnishes, the result is a durable, elastic, highly adherent and resistant product, not only to abrasion, but also to other products or liquids.
Forms: It is one of the most common and versatile types of varnish, and its use is very widespread. Floors or platforms, coverings, doors, windows, friezes and in general all types of carpentry.
There are three types:
- Varnish Polyurethane Urea Formol Base. It practically disappeared from the market because it is toxic. It stood out for offering a shiny and abrasion resistant finish. It gave a lot of problems in contact with the water.
- Solvent-based Polyurethane Varnish. It is characterized by being a product of great resistance and durability. It has been the most common type of finish for wood for many years, but is being replaced by water-based varnishes, which are significantly more environmentally friendly and less toxic.
- Water-based Polyurethane Varnish. This type of varnish is representing a revolution in the sector not only because it is less polluting, but also because manufacturers have been improving its composition. Now they are much stronger than those made a decade ago. In that sense, they have little to envy solvent-based polyurethane varnishes. Although on the other hand they have a higher price.
Characteristics: Wood varnishes obtained from acrylic resins offer a soft and durable touch. They also dry quickly, do not yellow or change the colors of the surface where they are applied (as long as it is transparent).
Forms: These characteristics make acrylic varnishes widely used to protect the colors of decorative items, protect other finishes, works of art, etc.
Disadvantages: As a main disadvantage, it stands out that its resistance to abrasion is limited, so it should not be used on surfaces that will undergo continuous use.
They are available both water-based and solvent-based.
Synthetic Wood Varnishes
Synthetic varnishes are obtained from alkyd resins, so they are also known as alkyd varnishes.
Characteristics: They are characterized by having great resistance, both to abrasion and moisture, and by being elastic. Therefore, it is mainly used on surfaces exposed to the elements. Taking into account the type of use to which it is subject, it is common for manufacturers to add substances such as UV filters, fungicidal agents …
Forms: It is used in outdoor carpentry (doors, windows, coverings …), outdoor furniture, boats or public furniture.
Usually the so-called marine varnish, used not only on boats, but also on docks, walkways, etc., is a synthetic varnish of this type.
As its name indicates, it is obtained with epoxy resins.
Characteristics: It is a highly resistant two-component varnish, both chemical and abrasion resistant, waterproof and flexible. Normally shiny finish.
Forms: It is also used in industrial areas and in the protection of metals. As a varnish for wood, it is used outdoors where high protection is needed, such as the deck of boats.
Nitrocellulose or Nitro Varnish
Nitrocellulose varnishes are compounds based on nitrocellulose, resins, solvent and plasticizer. Its hardening is physical and is based on the evaporation of solvents.
Characteristics: They stand out for offering a smooth and shiny finish of great beauty, highlighting the natural grain of the wood.
Disadvantages: Low resistance to abrasion, heat, cleaning products and yellowing when exposed to the sun.
Forms: Surfaces where you want to maximize the beauty of the material, for example in works of art, musical instruments, turning and carving, antiques, etc. It is a modern substitute for shellac and waxes.
It is mainly applied by spray and the drying times vary between 20-50 minutes for the first coat and between 30-60 minutes for the following.
Characteristics: High hiding power, due to reduced solvent volatilization, shine and silky texture. The result is a surface with great physical and chemical resistance, and also very stable over time.
Disadvantages: It has little resistance to atmospheric agents (sunlight, humidity, etc.) and is not very elastic.
It can be in combination with or without paraffin. The former prevent air from coming into contact with the varnish during drying. Therefore, it is much slower. When using paraffin, it is necessary to clean the residue later.
Forms: They are mainly used in furniture and interior decoration, doors and kitchen fronts … Also in areas where high gloss is desired.
Note: Resinous woods always require the application of primer or impregnation. In the case of polyester varnishes it is even more important if possible, since it is possible that the polyester will not dry.
Shellac, also known as shellac, is a type of natural varnish obtained from the secretions of an insect in combination with alcohol. They are applied with a crank pin, and can be purchased in discs (the purest), in flakes or in colors.
Characteristics: It has amber tones and has medium resistance to abrasion.
Disadvantages: Does not withstand high temperatures or contact with some chemicals (some common in cleaning products).
Forms: It has been used for hundreds of years in musical instruments, crafts, furniture and antiques restoration.
Types of wood varnish according to the finish
Each product has its own characteristics, and not all allow the level of brightness to be varied in the same way. In the case of varnishes, the usual are the glossy finishes. Satin finishes are frequent and matte finishes are much less. In the latter case, many products offer a poor result.
Depending on the gloss level, we can classify the types of wood varnish as:
- Brightness. High level of brightness. They give strength and shine to the wood, although on the other hand they allow imperfections to be more visible. The result is not natural.
- Companion. Matte varnish. In wood, matte finishes allow you to appreciate the natural colors of wood to a greater extent.
- Satin. Medium brightness level.
Types of wood varnish according to the type of drying
As already mentioned, the varnish is applied in a liquid state on the surface to be protected.
Usually drying occurs due to the evaporation of solvents in contact with air. In these cases it is not necessary to use another product to force this process, they are called varnishes. single component.
At other times, it is essential to use a catalyst that makes the varnish react to produce drying. these are the two-component varnishes.
The latter offers superior strength and toughness. These are used to a greater extent in metals and a little less in wood, being limited to very demanding uses, such as urban furniture, boats, etc.
Types of wood varnish according to shape
You can buy varnishes in different formats. Obviously, the most common is can. We can find them with contents ranging from 100 ml or less to several liters.
Varnish Spray. This format is becoming more common among DIYers. It’s because they allow a better finish than we would get with a brush and makes cleaning a lot easier. Although on the other hand it has a higher price.