There are several methods to improve and / or allow the use of wood outdoors. This is an increasingly common demand, given the resurgence of interest in wood for uses for which it had been forgotten for years.

This time we will refer to one of the most innovative treatments, acetylated wood. With this, it is possible to achieve a class 1 durability with coniferous species, a classification that only some tropical species achieve naturally.

The process itself is not new, the first patent relating to the acetylation process dates from 1930. However, it was only in the 19th century that large-scale industrial processes for production were developed.

What is acetylated wood?

Acetylated wood is a type of treated wood to improve its performance outdoors. With this process, which eliminates the use of toxic products, the internal structure of the wood is modified, reducing its ability to absorb moisture.

Among the advantages of this type of treatment, in relation to other alternatives, is the conservation of resistance, hardness and natural aspect of the wood, with emphasis on the substantial improved stability (reduced movement).

The wood that undergoes the process most often is pine, although others such as oak or even iroko are also common.

Uses of acetylated wood

Due to its excellent performance against external agents, its main uses are: urban furniture, pavements and exterior carpentry (doors, windows, frames …), facade cladding, construction, etc.

As already mentioned, acetylated wood can be classified in terms of durability as Class 1. Therefore, in terms of classes of use it reaches 3.1 (external wood without contact with the ground and protected), 3.2 (external wood without contact with the ground and without protection) and 4 (external wood in contact with the ground). All of this in accordance with European regulations.

It is estimated that it can last about 25 years in direct contact with the ground and 50 if it is not in contact.

What is the transformation process?

As we all know, wood adapts continuously to the humidity level of the environment. It absorbs and releases water continuously, which produces contractions and expansions.

With the wood acetylation process, the goal is to reduce this natural water absorption by the wood. From a chemical point of view, free hydroxyls are responsible for absorbing moisture. With acetylation, it is possible to convert these free hydroxyls into acetyl groups, significantly reducing the wood’s ability to absorb water.

For this, acetic anhydride is used, which comes from acetic acid (being diluted is known as vinegar). In addition, during the process, high temperature and vacuum cycles are required to achieve the desired reaction.

In addition to the mentioned change, it is common for wood to increase its density between 1-8%.

Advantages of acetylated wood

There are other treatments to preserve wood outdoors. Some are superficial, others also modify the structure of the wood. Each has its advantages and disadvantages. In the case of acetylated wood:

  • The durability of the wood is considerably improved.
  • Maintenance needs are drastically reduced.
  • The dimensional stability of the wood is improved. Contractions and expansions are reduced by between 70 and 80%.
  • Resistant to fungi and insects. In fact, because it is a different type of wood, insects do not identify it as such. That is, it is not digestible by insects such as termites or woodworm.
  • Maintains the natural look of the wood, the change in tone is almost imperceptible. This is a great advantage of the acetylation process, as other methods such as autoclaving or carbonization change it considerably.
  • The natural characteristics of each wood in relation to hardness and resistance are not significantly changed.
  • It can work normally. Cut, plan or machine smoothly and without the use of additional chemicals or special machinery.
  • Can be used in marine environments: walks, marinas, swimming pools …

An indirect benefit of acetylated wood is that its use reduces the demand for tropical wood species, many of them at risk due to overexploitation. Not only that, it also reduces the use of potentially harmful chemicals that are sometimes used to preserve wood outdoors.