Using timber in situations that are open to the elements means that suitable species need to be selected. In the UK, home hardwood species are really down to two options that are durable, Oak or Chestnut. For softwoods Larch or Douglas Fir. The two hardwoods have good durability, and the softwoods moderate durability. However, another way to approach the issue of durability in the open air is tanalised or thermally modified timber. Whether you are building a deck, fence, or any other outdoor structure, selecting the right type of timber is crucial. Particularly when it comes to ensuring that it remains strong and sturdy, even in adverse weather conditions.

Tanalised or thermally modified timber are possibilities. Both of these types of timber have unique properties that make them suitable for outdoor use. Each has its advantages, disadvantages and specific uses.

In this blog, we will take a closer look at these two types of timber and compare their properties to help you make an informed decision when choosing the right type of timber for your outdoor projects.

What is Tanalised Timber?

Tanalised timber, also known as pressure-treated timber, is a type of timber that has been treated with a preservative to make it resistant to rot, decay, and insect attack. The process of tanalising involves placing the timber in a vacuum chamber and then filling it with a preservative solution, which is forced deep into the wood fibres under pressure. As a result, this ensures that the preservative penetrates the timber thoroughly, making it resistant to rot and insect attack.

Pros and Cons of Using Tanalised Timber for Outdoor Projects

One of the main advantages of using tanalised timber for outdoor projects is its affordability. Tanalised timber is readily available and is generally less expensive than other types of treated timber. It is also effective at preventing rot, decay, and insect attack, which can prolong the life of your outdoor structure. This is due to the chemicals being poisonous to wood-destroying fungi.

However, there are some potential downsides to using tanalised timber. The chemicals used in the treatment process need to be handled carefully in the preservation process. This is to ensure they do not pose a health risk. Further, the timber may require ongoing maintenance to prevent weathering and fading. Where the treated timber has been cut to length, the cut surfaces must be treated before installation.

Where a machined finish is required, the machining should be done before the treatment process. In wide terms, tanalised timber is mainly used for softwood fencing and gates.

Finally, some people may prefer a natural, untreated look for their outdoor projects, which tanalised timber cannot provide as easily as thermally modified timber.

What is Thermally Modified Timber?

Thermally modified timber is a type of timber that has been heat-treated to make it more durable and resistant to decay, moisture, and insect attack. During the thermal modification process, the timber is heated to a high temperature in a low-oxygen environment, which causes chemical changes in the wood fibres. These changes make the timber more stable, less prone to swelling and warping, and more resistant to decay and insect attack.

To learn more about the process of thermo-treated timber, check out our recent blog post: Why Thermo-Timber is the Future of British Hardwoods.

Pros and Cons of Using Thermally Modified Timber for Outdoor Projects

One of the main advantages of using thermally modified timber for outdoor projects is its durability. The thermal modification process significantly improves the timber’s resistance to moisture, decay, and insect attack, making it ideal for use in harsh outdoor environments. It also has a unique, natural appearance that can add aesthetic value to your outdoor structure.

However, there are some potential downsides to using thermally modified timber. The thermal modification process can be more expensive than other types of timber treatments, which may increase the cost of your outdoor project. Additionally, while the timber’s natural appearance may be appealing to some, others may prefer the look of treated timber. Finally, it is important to note that thermally modified timber may still require ongoing maintenance, such as regular oiling or staining, to prevent weathering and fading over time.

Tanalised vs. Thermally Modified Timber: Key Differences

Although both types of modified timber are similar, there are a few key differences.

When it comes to choosing between tanalised and thermally modified timber for outdoor projects, the decision ultimately depends on the specific needs of your project. Tanalised timber is great for those on a budget, as it is generally less expensive than thermally modified timber. It is also effective at preventing rot, decay, and insect attack. However, it requires ongoing maintenance to keep it looking its best.

Alternatively, thermally modified timber is more durable and stable, making it ideal for harsh outdoor environments. While it is more expensive than tanalised timber, it requires minimal maintenance and has a unique, natural appearance that can add aesthetic value to your outdoor structure.

Generally, if your outdoor project will be exposed to a lot of moisture, such as a deck or a fence near a pool, then thermally modified timber may be the better choice. This is due to its superior resistance to moisture. However, if you are on a budget and are willing to perform regular maintenance, then tanalised timber may be a more practical option.

Environmental Impact of Tanalised and Thermally Modified Timber

When it comes to the environmental impact of tanalised and thermally modified timber, there are several factors to consider. The treatment process for tanalised timber involves using chemicals that can be harmful to the environment if not disposed of properly. Therefore, it’s important to source tanalised timber from a credible and responsible source. In addition, some of the preservatives used in tanalised timber have been linked to health concerns, which may be a concern for those who are environmentally conscious.

Thermally modified timber, on the other hand, does not involve the use of chemicals, making it a more environmentally friendly option. The thermal modification process uses heat to alter the wood fibres, rather than chemicals, which means that it does not pose the same risks to the environment. Additionally, the process of thermal modification can be carried out using renewable energy sources. As a result, this further reduces its environmental impact.

In terms of sustainability, both tanalised and thermally modified timber can be sourced from sustainable forests. However, it is important to note that the availability of sustainably sourced timber can vary depending on the region and supplier.

Overall, while both tanalised and thermally modified timber have their advantages and disadvantages when it comes to environmental impact and sustainability, thermally modified timber is generally considered to be the more eco-friendly option due to its lower use of chemicals and potential for renewable energy use during the production process.

What treated timber is on offer at W L West & Sons Ltd?

We stock a variety of tanalised timber as fencing products serving West Sussex and the surrounding areas. For thermally treated species, we have suppliers with good stocks, although it may not be available in all sizes. 

To conclude, both tanalised and thermally modified timber have their advantages and disadvantages. The decision on which to use ultimately depends on the specific needs of your project. With the information presented in this article, we hope that you are better equipped to make an informed decision and create a beautiful, durable, and environmentally responsible outdoor structure.

WL West Timber is a family-owned sawmill & timber merchant in West Sussex with over 155 years’ industry experience. We provide a wide range of air-dried oak and kiln-dried oak timber products and supplies. We also build and install custom projects for our customers.

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