Timber preservation is essential for extending the life, durability, and overall quality of wood used in construction and other applications. Various preservation techniques and materials protect timber from insects, fungi, and other sources of decay. When timber is properly preserved, it resists environmental damage and stays stronger for a longer period, enabling its use in more demanding settings. Without preservation, timber is susceptible to disease and deterioration, potentially reducing its lifespan and utility. This article explores the properties of effective preservatives, different preservative types, and methods of application to enhance timber longevity.
1. Properties of Good Timber Preservatives
An effective preservative must meet certain criteria to ensure it protects timber efficiently and safely:
- Availability and Cost: A good preservative should be easy to obtain and affordable, ensuring it can be applied broadly.
- Non-Toxicity: It should not contain harmful substances or emit toxic gases.
- Economical Coverage: Small amounts should cover large areas, making the preservative economical to use.
- Surface Compatibility: Timber should still allow for surface treatments, like paint or decorative finishes, after the preservative is applied.
- Strength Preservation: The preservative must not weaken the timber’s structural integrity.
- Neutral Odor: It should avoid unpleasant smells, ensuring it doesn’t affect surrounding environments.
- Environmental Resistance: Effective preservatives should resist degradation from light, heat, or moisture.
- Pest and Fungi Protection: The preservative should repel and ideally kill insects and fungi.
- Fire Resistance: Non-flammable preservatives add a level of fire protection.
- Non-Corrosive to Metals: The preservative should not cause metal fixtures to corrode.
- Penetration Depth: The preservative should penetrate the wood fibers deeply enough, typically 6mm to 25mm, to ensure lasting protection.
2. Types of Timber Preservatives
Different types of preservatives are applied based on the intended use and conditions of the timber. Here are several commonly used types:
- Coal Tar
Coal tar is applied hot using a brush, providing a protective, fire-resistant coating. However, it emits a strong odor and does not permit painting. Commonly used on door and window frames, coal tar is economical and durable. - ASCU (Arsenic-based) Preservative
ASCU is a powder that, when dissolved in water, creates an odorless solution. It is highly effective in preventing white ant infestations. ASCU contains ingredients like hydrated arsenic pentoxide, copper sulfate, and sodium or potassium dichromate. Once applied, timber can be painted or varnished. - Chemical Salts
Chemical salts such as copper sulfate, mercury chloride, and zinc chloride are dissolved in water and provide an odorless, non-flammable preservative solution. These salts are commonly used to protect timber from biological threats. - Oil Paints
Oil paints, applied in multiple coats, are suitable for seasoned wood. They provide moisture resistance, but if applied to unseasoned wood, they can trap sap, leading to decay. Oil paints are mainly used for finished wood that requires protection from moisture. - Solignum Paints
Solignum paints are applied hot, providing effective protection against white ants. These paints can also include color pigments to give the timber an aesthetically pleasing appearance. - Creosote Oil
Made through tar distillation, creosote oil is black or brown and has a strong odor. It’s applied under high pressure in an airtight chamber, allowing the timber to absorb it thoroughly. Due to its flammability, creosote oil is not used in fireplaces but is effective for wood piles, poles, and railway sleepers.
3. Methods of Timber Preservation
The application of preservatives varies in complexity, with each method tailored to different types of wood and protective needs. Here are common methods:
- Brushing
Brushing is a straightforward method, where the preservative, often heated, is applied to well-seasoned timber using quality brushes. For optimal protection, multiple coats are applied with appropriate intervals between each. - Spraying
Spraying involves using a spray gun to apply the preservative solution, which is quicker and often more effective than brushing. This method is especially useful for large timber surfaces that require swift coverage. - Injection Under Pressure
In this high-pressure technique, the preservative is injected directly into the wood, allowing for deep penetration. Commonly used with creosote oil, this method requires specialized equipment and is costlier, but it offers long-lasting protection. - Dipping and Stepping
Dipping involves submerging the timber in a preservative solution, allowing for better penetration than brushing or spraying. In some cases, timber is left to soak for days or weeks, known as the stepping method, to maximize absorption and durability. - Charring
Charring, one of the oldest methods of preservation, involves burning the timber surface to a depth of approximately 15mm. This burnt layer protects the inner wood from insects and fungi, making it ideal for wood fencing poles and the bases of telephone poles. - Hot and Cold Open Tank Treatment
In this method, the timber is placed in a tank with preservative solution, which is then heated to 85–95°C. After heating, the solution is cooled gradually, allowing the timber to absorb the preservative deeply as it submerges. This method is typically used for sapwood.
Timber preservation enhances the wood’s lifespan, making it more resistant to environmental and biological threats. By using effective preservatives and appropriate application methods, timber can be made durable enough to serve a wide range of purposes, from construction to outdoor structures. Properly preserved timber is a more sustainable choice, ensuring it can withstand time, weather, and pests effectively.