Timber is a timeless building material, loved for its natural beauty and inherent durability. However, when timber is exposed to the elements or used in outdoor applications, it needs extra protection to ensure it lasts for years to come. That's where pressure treatment comes in. This process significantly enhances timber's resistance to decay, insects, and weathering. But what exactly happens to timber when it's pressure treated? This comprehensive blog post will explore the process, benefits, and uses of pressure-treated timber.

The Pressure Treating Process

Pressure treating is a method used to impregnate timber with preservatives, making it more resistant to environmental elements, decay, and pests. The process involves a few key steps:

1. Preparation

First, the timber is prepared, which includes cutting it to the desired size and drying it until it reaches the appropriate moisture content. The drying process is crucial as it allows the preservative to penetrate more effectively.

2. Treatment

The prepared timber is placed in a large, horizontal cylinder known as a pressure treatment vessel. The vessel is then sealed, and a vacuum is applied to remove air from the timber cells. Following this, the cylinder is filled with the preservative solution. Once the timber is fully submerged, pressure is applied to force the chemical deep into the wood fibres. The amount of pressure can vary but is typically around 150 pounds per square inch (psi).

3. Fixation

After the preservative has been applied under pressure, the timber is left to sit so that the chemicals can fix to the wood. This step ensures that the preservative won't leach out when the timber comes into contact with water or wet soil.

4. Finishing

Finally, the timber is removed from the vessel and left to dry. Once dry, it can be further processed, painted, or stained, depending on its intended use.

Types of Preservatives Used

The type of preservative used in the pressure-treating process can vary depending on the intended use of the timber and the level of protection required. Common chemical preservatives include Alkaline Copper Quaternary (ACQ), Copper Azole (CA), and Chromium Copper Arsenate (CCA). Each of these chemicals protects timber from decay, fungi, and insects to varying degrees, with some being more suitable for certain applications than others.

Benefits of Pressure-Treated Timber

The primary benefit of pressure-treated timber is its enhanced durability and longevity. Treated wood can withstand harsh outdoor conditions and resist decay, termites, and fungal growth. This makes it an ideal choice for structures like decks, fences, and garden furniture. Additionally, pressure-treated timber is a more cost-effective alternative to naturally durable woods such as cedar or redwood.

Applications of Pressure-Treated Timber

Due to its durability and resistance to decay, pressure-treated timber is widely used in outdoor and ground contact applications. Common uses include:

  • Decking and garden patios
  • Fences and railing systems
  • Playsets and outdoor furniture
  • Landscaping timbers and retaining walls
  • Piers, docks, and boardwalks

Safety Considerations

While pressure-treated timber offers numerous benefits, it's essential to handle and work with it safely. Cutting, sanding, and drilling treated wood can release dust and particles that may be harmful if inhaled or ingested. Always wear protective gear such as gloves, masks, and goggles when working with pressure-treated timber. It's also advisable to wash hands thoroughly after handling and to avoid burning treated wood, as the smoke can be hazardous to health.


Pressure-treated timber represents a significant advancement in extending the life of wood used in outdoor environments. Through the careful application of preservatives under pressure, timber becomes more durable and resistant to natural decay processes. This makes it an invaluable material for construction and outdoor projects, guaranteeing that the beauty and utility of timber structures endure for many years to come. Always remember to follow safety guidelines when handling and working with treated timber, ensuring both the longevity of your projects and your health.