The Differences Between Pressure Treated and Thermally Modified Wood

When it comes to choosing lumber for outdoor projects, two common options are pressure treated lumber and thermally modified wood. While both types of wood can be used in similar applications, they differ in several key ways. Here are some of the main differences between pressure treated lumber and thermally modified wood:

Treatment Method

Pressure treated lumber is treated with chemicals to protect against decay and insects. The wood is placed in a pressurized cylinder, and a solution of water and preservative chemicals is forced into the wood. This process makes the wood resistant to rot and insect damage.

Thermally modified wood, on the other hand, is treated with heat and steam. The wood is placed in a kiln and heated to a high temperature (usually around 400 degrees Fahrenheit) in the absence of oxygen. This process changes the chemical structure of the wood, making it more stable and resistant to decay.

Appearance

Pressure treated lumber typically has a greenish tint, due to the chemicals used in the treatment process. This can be a disadvantage if you're looking for a natural wood look. However, pressure treated lumber can be stained or painted to match your desired look.

Thermally modified wood, on the other hand, has a rich, natural color that varies depending on the type of wood used and the specific heating process. The wood can be left untreated, or finished with a clear coat or stain to enhance its appearance. Thermally modified wood can perform outside with no applied finishes or coatings and if left unfinished will develop a beautiful silver patina.

Durability

Both pressure treated lumber and thermally modified wood are more durable than untreated wood. However, the durability of pressure treated lumber can vary depending on the specific chemicals used and the quality of the treatment process. In general, pressure treated lumber is expected to last around 20-30 years.

Thermally modified wood, on the other hand, is expected to last even longer - up to 30 years or more. This is due to the changes in the wood's chemical structure, which make it more resistant to decay and insect damage. It is also more stable and resistant to the impact of changes in moisture and humidity that can cause boards to warp, twist, or expand.

Environmental considerations

Both pressure treated lumber and thermally modified wood have some environmental considerations to take into account. Pressure treated lumber is treated with chemicals that can be harmful to the environment and to human health, particularly if the wood is burned or disposed of improperly. The chemicals can also leach out into the ground, contaminating groundwater and impacting the surrounding environment.

Thermally modified wood, on the other hand, is treated with heat and steam, which is a more environmentally friendly process. There are no chemicals used in the entire process. At the end of its life it can be recycled or repurposed for many other uses.

When it comes to the built environment both pressure treated lumber and thermally modified wood have their pros and cons as well as their time and place. Pressure treated lumber is a more affordable option that can be used in a wide range of applications, while thermally modified wood offers a more natural look and longer durability. When choosing between the two, consider your budget, the desired appearance, and your environmental concerns.