Preservation of Timber | Civil Engineering Optional Notes for UPSC PDF Download

Timber preservation refers to the process of applying a layer of a preservation material such as oil on timber to protect it from insects, moisture, etc.
Preservation helps increase the life of the timber. A variety of preservatives are used for this purpose. Some timber preservatives can also change the colour and appearance of the wood, making it more attractive for a project.

Importance of Timber Preservation

Timber preservation is crucial for extending the life of wood by improving its durability and resistance to elements such as insects, moisture, and weathering. Applying a quality preservative before using timber in a project ensures long-lasting performance and minimal maintenance. Without preservation, timber can degrade faster than expected, becoming susceptible to insect and fungal damage. Preservation also protects against water damage, especially important in areas like bathrooms and kitchens.

What is a Wood Preservative?

A wood preservative is a chemical applied to wood to add a protective layer. It enhances the wood's durability and resistance to weathering and other damaging factors. An ideal preservative should:

• Be easy to apply and cover large areas quickly.
• Be free from harmful chemicals.
• Be cost-effective and readily available.
• Enhance the wood’s strength and durability.
• Be odorless or have a pleasant smell.
• Resist rot, insects, fungi, and moisture.
• Be fire-resistant.
• Be stable under light and heat.
• Be anti-corrosive.
• Penetrate deeply into the wood.

Types of Timber Preservatives

Various preservatives are available, each suitable for different wood types and applications. Common types include oil-based preservatives, water-soluble preservatives, and solignum paints.

Oil-Based Preservatives

1. Coal Tar:

   • Thick liquid oil that is heated to create a lighter tar for easy application.
   • Applied with a brush, mainly for outdoor and marine timber.
   • Offers resistance to fire and water.
   • Drawback: It doesn’t allow paint application.

2. Oil Paints:

   • Protects wood against moisture.
   • Requires well-seasoned wood for application.
   • Applied in multiple coats for strong protection.
   • Can lead to timber decay if used on unseasoned wood.

3. Creosote Oil:

   • Derived from the purification of coal tar.
   • Dark brown to black, less thick than tar.
   • Applied to seasoned timber to protect against termites and water.
   • Commonly used for railway sleepers and poles.
   • Non-corrosive with an unpleasant odor.
   • Does not allow paint application.

Water-Soluble Preservatives

1. ASCU:

   • Powder mixed with water in a 6:100 ratio.
   • Applied by spraying to protect against insects, especially white ants.
   • Allows for painting after application.

2. Chemical Salts:

   • Dissolved in water to create a preservative solution.
   • Enhances wood strength, is anti-inflammatory, and odorless.
   • Common examples include copper sulphate, mercury chloride, and zinc chloride.

Solignum Paints

• Chemical-based wood preservatives available as termiticides and decorative coatings.
• Protect against various insects, including white ants.
• Available in different colors, enhancing the wood's appearance.

Using the appropriate type of preservative based on the timber and its intended use ensures optimal protection and longevity.

Methods of Applying Timber Preservation

Timber preservation involves applying a preservative to wood to enhance its durability and resistance to various elements. This process is typically done during wood processing, after the timber has been properly dried. Different methods can be used to apply preservatives, depending on the type of wood and its intended use. Here are some common methods:

1. Preservative Application on Timber Surface
​​This involves applying preservatives directly on the wood surface by spraying, brushing, or dipping.​​

1.1 Brushing

• A brush is used to manually apply preservatives to the wood surface, ensuring all sides of the timber are properly coated.

1.2 Dipping

• The timber is submerged in a container filled with a preservative solution and left for a specified period, allowing the preservative to fully cover the wood surface.

1.3 Spraying

• A sprayer machine is used to apply the preservative solution to the wood surface. This method is quicker and more efficient than brushing but less effective than dipping.

2. Preservative Soaking Application

• Freshly sawn wood is dipped in a pool of preservatives and left to soak for a considerable period. The soaking time depends on the timber's type and thickness. Thin veneers need only a few minutes, while thick boards require more extended soaking periods.

3. Injecting Under Pressure

• Preservatives are injected into the timber by applying pressure under specific temperature conditions. This method, which often uses creosote oil or other suitable preservatives, requires specialized equipment and can be expensive.

4. Hot & Cold Timber Preservation

• Timber is dipped in a pool of preservative and then heated to a predefined temperature. This causes the air inside the timber to expand and leave the wood. The timber is then cooled, causing the remaining air inside to contract and the wood fibers to absorb the preservative, filling the vacuum inside. This method also sterilizes the timber, making it free from fungi and insects and achieves similar results to the pressure treatment method.

5. Timber Preservation Using Charring Method

• This traditional method involves burning the timber surface up to 15mm to create a natural protective layer. The timber is first submerged in water for up to 30 minutes and then burned. This treatment is generally used for fencing poles and is not suitable for outdoor wood applications.