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What is Accoya and why should you consider it for your sash window?

Accoya® wood is the result of decades of research and development that has brought together a long-established, extensively proven wood modification technique and leading-edge patented technology – acetylation to create a high performance wood, ideal for outdoor use and challenging applications. Last year we announced we would use Accoya for all our painted joinery. It’s a fantastic material that performs well in a wide range of applications. We often use it for our sash windows. As such, to help you discover more about this material, we caught up with Accoya to ask some much needed questions:

How is Accoya® wood made?

The technology behind Accoya® is based on wood acetylation. The process essentially alters the actual cell structure of wood by transforming free hydroxyl groups into acetyl groups. Acetyl groups simply consist of hydrogen, oxygen and carbon and are already present in all wood (ranging from 1% to 8% by weight) and can be derived independently from acetic acid, i.e. vinegar. Thus, the process does not introduce anything to the wood that does not naturally occur in it.

What benefits does Accoya® have over unmodified wood?

Unmodified wood has ‘free hydroxyl groups’ that absorb and release water as climatic conditions change, making it prone to expansion and contraction, particularly when used outdoors (windows, doors, cladding, etc), which in turn leads to splitting and rotting. During the Accoya® production process, the free hydroxyl groups within the wood are changed into acetyl groups and this reduces the ability of the wood’s cell walls to absorb water by approximately 80%, greatly improving the wood’s dimensional stability and resulting in reduced maintenance frequencies for coatings. In addition, the change in cell structure means that fungi do not recognise Accoya® as wood and therefore do not attack it. Insects that attempt to eat the wood die of starvation because the modified structure makes it indigestible, so that it is no longer a source of food.

How does Accoya® differ from wood that has been impregnated or modified in other ways?

Virtually all wood preserving treatments today work by impregnating toxic chemicals (such as arsenic, oils, ammonia or metal compounds) into the cell walls of the wood, filling the voids but not changing the underlying chemistry of the wood. This controls unwanted organisms, such as bacteria, viruses and fungi, by creating an inhospitable environment.

However, the toxicity of such products has environmental implications, both during the serviceable life of the wood and for its safe disposal. By contrast, Accoya® wood is non-toxic and 100% recyclable.

The main non-toxic preservative treatment available is a “thermal modification” process which works by breaking down the edible components of the wood. However, the process both discolours and weakens the wood, rendering it unsuitable for many uses.

How can the quality of Accoya® be guaranteed?

In contrast to other modification techniques, it is possible to measure the quality of Accoya® by determining the acetyl content of the wood once it has been modified by measuring and analysing the percentage of acetyl groups present. Using an array of sophisticated and proven analytical techniques, Accoya®’s producers ensure that every batch is of consistent quality and reaches the highest performance standards.

How environmentally friendly is Accoya®?

Accoya® wood is non-toxic and 100% recyclable.

Does Accoya® have different paint-ability?

Yes. Due to the improved dimensional stability of Accoya® wood, which ensures it is significantly reduced swelling and shrinking, maintenance of the coating system can be increased to 3 to 5 times normal life. Extensive tests have shown better coatings adhesion and reduced costs in applying coatings in a manufacturing environment.

Find out more about Accoya and our sash window service where we offer draught proofing, full restoration, double glazing and complete new windows.

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