1st Feb 2017
To quote Josh Hudson, BarrJoinery Director, “What was the first thing we did when we got hold of a piece of treated wood which we were told did not degrade, warp or swell? … We put a it into water and waited!" Apparently this is a common response. There must be hundreds of pieces of acetylated wood sitting in pots of water in joinery workshops across the world. In fact the company producing acetylated wood (trade marked Accoya) have started producing labeled samples asking customers to do just that. They are confident that after intensive testing over 75 years in development their product is bullet proof (or should I say waterproof)…and lets face it, in the UK all external joinery gets wet!
Actually ‘waterproof’ is not technically correct. 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). This in turn leads to splitting and rotting. Accoya is timber which has been dried and chemical treated to prevent the water absorption and release process - thus stabilising the wood for an extended time periods.
The acetylation process involves treating the timber in a pressure chamber which forces acetic anhydride to react with the wood at a molecular level. The free -OH (hydroxyl) groups within the timber cell wall are replaced by acetyl groups, a compound which occurs naturally in unmodified timber. These non-toxic acetyl groups are hydrophobic and prevent water bonding onto the cell wall and so prevent the water causing swelling of the wood or providing a food source for the fungus and attacking insects that bring about decay, resulting in the highest durability class possible (class 1 in EN 350). The bi-product of this process is acetic acid, otherwise known as vinegar in its dilute form, which can be reused in a wide range of industries including the food industry
Besides forming a natural ecological habitat the forests from which the timber is sourced are an important carbon sink, as they filter CO2 out of the air and absorb it into the biomass of the tree as biogenic carbon. The sustainable use of wood in durable products reduces the rise in CO2 levels in the atmosphere, thus acting as a brake on the greenhouse effect. To produce Accoya, only abundantly available wood species are being used from certified, sustainably managed forests and plantations, including FSC and other regionally certified woods. Therefore all Accoya is compliant with the European Union Timber Regulation (EUTR) as well as the Lacey Act, and therefore responsible production is guaranteed. Fast growing softwood species such as Radiata Pine are primarily used to produce Accoya. Considering the increasing pressure on available resources, the use of wood species that produce larger volumes of wood over the same time span for the same area of land offers obvious environmental advantages. Click here for more information.
There are other treated woods on the market - but they differ significantly acetylated wood. Virtually all wood preserving treatments today work by impregnating 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. 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.
Unlike other treated timbers Accoya wood is modified all the way through, not just at the surface layer like many alternative treatments. This means that users can have absolute confidence in Accoya’s durability in a way that has not previously been possible. When Accoya is cut or jointed there are no exposed un-acetylated surfaces in any dimension. This completely negates the need to apply additional chemical preservatives on-site, as is necessary with unmodified or envelope treated woods. From a construction and joinery perspective this is really good news!
An added bonus is that whatever Accoya is coated with maintenance of the coating system can be increased to 3 to 5 times normal life - again due to the increased stability of the wood. It is also possible to leave acetylated wood natural allowing it to beach and grey like any other untreated timber.
BarrJoinery are now a fully trained, accredited Accoya Joinery House. The workshop has completed several projects using acetylated wood and the Barr Joiners are enjoying getting to grips with this new timber. We asked senior Barr Joiner Duncan Glenn what Accoya is like to work with: “there are pros and cons from a workshop and fitting perspective; compared to oak Accoya is easier to machine but also easier to mark or dent, so naturally we have adjusted working practices in accordance.” Will BarrJoinery continue to use Accoya in the future? - we asked director Josh Hudson. “Naturally usage will be driven by client demand for the product. We offer a choice of timbers here at BarrJoinery, but given the compelling evidence for the acetylated timber and the growing knowledge and support base behind it, we can only see its usage increasing. Simply put… acetylated wood doesn’t swell, rot or warp which is great for us, for our customers and for the longevity of our finished products.”