Nowadays more and more people will choose thermally modified wood to decorate their courtyard, but have you any idea what thermally modified wood it is. What are the benefits for people of choosing this material? Today let’s talk about this topic.

Thermally modified wood is a kind of high temperature treated wood. Due to the special nature of the carbonization process, thermally modified wood has good anti-corrosive and environmental protection properties. Treat ordinary wood in a high temperature environment, and then the surface of the wood will form a dense and hard carbonized layer. Such a carbonized layer can well protect the wood itself from the external environment such as wood rot fungus. The effects of insect ants, etc., effectively maintain the characteristics of the wood itself. The specific logic is that the thermally modified wood has undergone a high temperature treatment, and the internal structure and nutritional properties of the wood have changed greatly, so bacteria and insects cannot grow inside the wood.

Woods that are processed under the carbonized treatment has beautiful natural look, durable, rot resistant, pest resistant, weather resistant, fire resistant, UV resistant and  100% environmentally friendly. That is why more and more designer also choose it as ideal material for outdoor and indoor furniture in the past years.

flower pot rack

Thermally modified wood classification

According to different carbonization and corrosion depth, thermally modified wood can be divided into surface carbonization, deep carbonization, and full carbon.

  1. surface carbonization

The surface carbonized wood is grilled with an oxygen torch, which has a thin carbonized layer on the surface of the wood. The change in the properties of the wood can be compared to the paint of the wood, but the wood grain on the surface can be highlighted to produce a three-dimensional effect.

thermally modified wood

  1. Deep carbonization

Deep carbonized wood is also known as fully carbonized wood and homogenous carbonized wood. It is a wood treated by high-temperature carbonization technology of about 200 degrees. Because its nutrients are destroyed, it has better anti-corrosion and insect-preventing functions. Because of its reconstitution of the water-absorbing functional group hemicellulose, the product has better physical properties.

Deep carbonization wood

Deep carbonized wood is a green and environmentally friendly product. It has anti-corrosion and insect-repellent properties, but it does not contain harmful substances. It not only improves the service life of the wood, but also no harm to human body and animals during the use of the production process.

Before and After wood deep carbonation

thermally modified wood feature
  1. Improved durability against decay;
  2. Reduced equilibrium moisture content;
  3. Consistent color through the piece;
  4. Improved dimensional stability;
  5. Slightly reduced bending strength;
  6. Reduced splitting strength;
  7. Resin removed;
  8. Reduced thermal conductivity;

3. Full carbonization

Now let us take a look at deep carbonization process flow.

thermally modified wood process

Phase 1: Temperature increase

The temperature in the kiln is raised rapidly to around 212°F, affecting the natural composition of the wood. Steam prevents the wood from checking in the high heat. The moisture content of the wood is reduced from 15 to 20% to nearly zero.

deep carbonized process

Phase 2: Thermal modification

The temperature goes even higher to reach target color levels, around 415°F. The higher and longer the heat, the darker the wood becomes throughout, giving domestic wood the look of desirable imported wood.  Steam is used to prevent the wood from burning in the high temperatures.

The natural acids and sugars are modified from the extreme heat, which changes the physical structure of the wood. The wood’s ability to absorb moisture decreases, making it less prone to rot and decay. The equilibrium moisture content (EMC) of the wood decreases. This means the swelling and shrinking of the wood material due to moisture variations can be reduced by up to 60% compared to unmodified wood.

Phase 3: Cooling & Re-Conditioning

The temperature is reduced by spraying water onto the wood and cooling. Conditioning and remoistening bring the wood moisture content around 4 to 6%.

carbonized wood cooling process

Final Step: Milling

The TMT (Thermally Modified Timber) raw stock is then processed by local mill workers to the desired specification. Common mill forms are siding, decking and flooring.

Surface carbonization process flow is below, we need 4 steps to finish.

Surface carbonization process flow is below, we need 4 steps to finish.

Step 1 burn the wood

Pay attention to the burning process:

Do not use maximum blown light to burn, otherwise you will get a blackboard, and you cannot get the effect you want.

Step 2 Brush the wood surface

Brushing the surface carbonized powder with a standard steel brush, This step is important of forming the three-dimensional texture of the carbonized wood surface.

Step 3 Wash the wood

Step 4 Finished the wood

Painting of wood with wax oil or water-based paint, then carbonization wood is finished.

Finished the wood

Let us watch below video to see how thermally modified wood is made: