Why are more people using thermally modified wood?

Over the last decade there has been a huge increase in demand for modified wood. One type is OrganoWood, which we looked at in a previous article. Another very popular alternative, which we will look at more in this article, is thermally modified wood, or as we call it here at EcoChoice, thermodified timbers.

What is thermally modified wood?

When wood is modified, you take the original, natural product and change it permanently, either by using chemicals, compressing it or by using heat, to permanently change it so that its properties are different from how it was originally.

Thermally modified wood, as its name suggests, uses heat to modify the wood’s internal structure. The wood is heated at temperatures that are generally greater than 180°c with oxygen removed to stop the wood from burning.

The process changes the chemical structure of the wood, making it more durable and stable. It removes organic compounds from the wood cells, meaning that the end product – the thermally modified wood – will not absorb water as much water, so it will expand or shrink less, giving you less warping and twisting boards. It also removes the sugary nourishment for insects and fungi, meaning that there is nothing left for them to eat. What is therefore left is a durable wood that is resistant to moisture, decay and insects.

Any wood species can be thermally modified, although there is no reason to thermally modify dense hardwoods as they are already naturally durable and resistant to rot, fungi, insects and moisture. The only benefit of thermally modifying hardwoods such as Oak is the change in appearance. Thermally modified wood is recognisable from the fact that is darkened in colour, having a rich, deep brown appearance that gives the timber a more tropical and beautiful look. That aside, the most likely woods to be thermally modified are softwoods.

Different types of thermally modified wood

There isn’t just one type of thermodified wood – there are a number of different ways to thermally modify wood, which involve using different technologies. The key types are:

Plato Process
The Plato Process is a two-step thermo modification process that originates from The Netherlands. It involves subjecting the wood (which has been saturated with water) to hydrothermal treatment at high pressure at temperatures between 160°c and 190°c. The moisture content of the wood is then reduced to 10% and the wood is then dry cured under pressure at temperatures between 170°c and 190°c. The whole process can take up to 7 days.

Oil Heat Treatment
Oil Heat Treatment (OHT-Process) is a one step process that originates from Germany and sees the wood heated in a bath of oil at temperatures of between 180°c and 220°c.

Retification
Originating in France, Retification is a one step process that sees wood which has less than 12% moisture content placed in a high nitrogen atmosphere with less than 2% oxygen content. The product is known as Retiwood or New Option Wood

Les Bois Perdure
Also originating in France as the name suggests, this is a one step process that sees freshly cut and dried timber heated using steam, which is created by using the leftover moisture in the wood.

ThermoWood
ThermoWood^® is a registered process that originates from Finland. It is also known as Premium Wood. Like the Les Bois Perdue process, it involves using steam and pressure, but it can also be used to treat green wood (i.e. recently cut wood that has not been dried to allow for the evaporation of internal moisture). The process takes up to 72 hours.

What are the advantages of thermally modified wood?

The key benefit of thermodified wood is that it makes abundant timbers such as pine and spruce more durable and stable so that they behave more like traditional hardwoods such as oak and maple, or like exotic hardwoods such as teak and ipe. In other words, woods that without thermal modification would not have lasted long when used outdoors are now able to be used for decking and cladding without the use of harsh chemicals. It is also less likely to warp, is more resistant to heat and weather, and as a result many thermally modified timber products are expected to last for at least 25 years. Many painting and coating manufacturers even prefer the use of thermally modified timbers as their inherent stability puts less stress on the film coating the timber.  

Whilst two of the main uses of thermally modified wood are for creating exterior timber decking and exterior timber cladding, you may be surprised to learn that thermally modified wood is proving particularly popular in the guitar making industry, where some guitar manufacturers use acoustic sound boards and electric guitar fretboards that are thermally cured to help prevent the warping and cracking that often results from seasonal changes in humidity. It has also been observed that thermally modified guitars tend to sound more like well broken in and aged instruments sooner than their non-thermally modified alternatives.

The other key benefit of using thermodified wood is the benefit on the environment. Key to that is that thermally modified wood is protected from the weather, rot, wear and tear etc. by heating it to naturally remove its nutrients, whereas the most common way to treat abundant but not naturally durable timber normally is to pump it with toxic chemicals. We explored this in some depth in this article, where we explained that the chemicals used are heavy metals such as copper, and that timber which isn’t Organowood or thermodified is likely to be, in essence, a sponge full of chemicals.

Thermally modified wood is therefore a great way to protect timber for exterior purposes, without having to use nasty chemicals that do great damage to our environment. Whilst it is a relatively new technology, it is one that we are seeing growing and evolving all the time, and we will keep watching to ensure that we offer the latest and most eco-friendly construction materials on offer.

Who are EcoChoice?
EcoChoice are specialist suppliers of certified timber and recycled plastic products for exterior works, including cladding and decking. We were formed in 2005 with the aim of promoting FSC certified timbers to the UK construction industry, helping customers to engage in a sustainable way instead of turning away from both the deforestation and plastic waste problems. We offer products from a wide range of different timber species, including Greenheart and Pituca.

We are passionate about supplying our clients with independently certified timber products while encouraging responsible and sustainable practices at the source level. To find out how we can help you and to get a quick, no-obligation quote, please call us on 0345 638 1340, email us on info@ecochoice.co.uk or for more information about our sustainable timber products, please visit our website https://slow.ecochoice.co.uk/