Accoya for geeks: how can acetylation create perfect wood for external joinery?

The usage of Accoya is a growing trend, especially in the external joinery projects. Not without a reason. It is sustainable, extremely durable, highly water resistant, and has a variety of applications, especially in the external joinery projects. One can wonder what gives Accoya those super, high-tech abilities? It is not magic but chemistry. Accoya owes its properties to acetylation.

Accoya External Joinery Project


What is Accoya acetylation?

The acetylation as a chemical process is not a new phenomenon, but the scale of its usage changed heavily over the years. Only recently we acetylate larger volumes of wood and that gave various new possibilities to use this process for large commercial projects.

Acetylation is a chemical reaction with acetic acid. It starts when wood is soaked in acetic anhydride and causes modification of proteins in cells what reduces the ability of wood to absorb water by even 80%. As acetylation is a chemical process, one could ask if Accoya is toxic or harmful to the environment. Fortunately, hydrogen, carbon and oxygen which take part in acetylation don’t make Accoya toxic.

Accoya External Joinery Projects


Why does the moisture content matter?

The moisture content is nothing else than the content of water in the material which in our case is wood. The moisture content in a freshly sawed wood is about 40-200% and in a regular, production wood is usually somewhere between 8 and 25%. The difference is huge then. Wood can change its qualities by gaining or losing the moisture and when this process happens too quickly.

Due to changes of moisture in relation to the surrounding environment, wood can change its size and become damaged or prone to fungal infections. That matters when we consider wood durability or when changes in size can cause problems with windows and doors movement.

Would you like to start a conversation about Accoya timber? Send us a message at You could also watch a video about Accoya here.

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