8.3 Finishing Woods

Finishing Processes for Wood

  • Finishing processes are essential to enhance aesthetics and performance, as well as to prevent decay in wood products.

  • Specific finishes are suited for various applications based on desired outcomes, such as moisture resistance and aesthetic appeal.

Effects of Finishes on Wood

  • A finish can change the colour of the wood, enhance the natural grain pattern, or add texture to the surface.

    • Treatments protect wood by:

    • Increasing moisture resistance

    • Guarding against insect and fungal attacks

  • Seals timber to make it easier to clean and to protect against airborne pollutants.

Application and Preparation of Finishes

  • Good preparation of the wood substrate is crucial for effective finishing.

  • Steps for preparation include:

    • Sanding timber smoothly along the grain

    • Using methylated spirit to rub down timber for removal of surface dust and grease, which is essential for good adhesion.

  • Finishes can be applied using various tools such as:

    • Brush

    • Cloth

    • Roller

    • Pad

    • Spray

  • Some finishes require professional application, such as pressure-treated finishes.

User Applied Finishes

  • Finishes can be categorized into water-based and solvent-based options, typically applied by the user.

Polyurethane Varnish

  • Characteristics:

    • Tough, hardwearing finish with high resistance to heat, water, and chemicals.

    • A liquid plastic in a water- or solvent-based carrier, available in matt, satin, or gloss finishes.

    • Can be clear or tinted to enhance natural wood tones.

  • Common Applications:

    • Used on boats and wooden flooring.

    • Compatibility with sports hall flooring due to durability and water resistance.

Pros and Cons of Polyurethane Varnish

  • Pros:

    • Provides a lustrous finish.

    • More durable solvent-based versions have better wear resistance.

  • Cons:

    • Many are not UV resistant and can yellow over time.

    • Can give wood a plastic appearance.

    • Longer drying time and higher health risks associated with solvent-based versions.

Acrylic Varnish

  • Characteristics:

    • Milky-white appearance when wet but dries clear.

    • Faster drying time compared to polyurethane, does not yellow.

    • Commonly used as a topcoat over painted finishes.

    • Hardwearing but less resistant to solvents and heat than polyurethane.

    • Non-toxic and virtually odour-free.

Water-Based Paints

  • Uses:

    • Applied to provide opaque colour to wood, offering a wide colour range, can be diluted for translucency.

    • Low odour with low VOC levels.

    • Suitable for interior woodwork and furniture, known for being hardwearing and quick drying.

    • Many are certified as “Toy Safe”.

  • Recommended Practice:

    • Use of primer and undercoat is usually advised.

Stains

  • Function:

    • Water-based stains apply colour while preserving the natural grain of the wood.

    • Provides aesthetic value but lacks protective properties against decay and degradation.

  • Availability:

    • Offered in both bright colours and natural wood tones to mimic darker hardwoods for softwoods

Colour Wash

  • Characteristics:

    • Provides an artistic, distressed finish while accentuating product details.

    • Applied to previously painted surfaces and wiped off with a rag to create texture and depth.

  • Limitations:

    • Adds aesthetic appeal but does not provide wood preservation.

Wax Finishes

  • Benefits:

    • Easy application providing a natural look that nourishes and protects the wood.

  • Limitations:

    • Offers limited moisture, heat, and scratch resistance; requires regular reapplication.

    • Multiple coats needed for optimal protection.

  • Application Method:

    • Applied with a lint-free cloth, allowed to sink in, and buffed for shine.

    • Some waxes are food safe and non-toxic.

Oils

  • Purpose:

    • Used to replenish the natural oils lost over time, enhancing the wood's appearance.

    • Raw oils (e.g., coconut oil, sunflower oil) are non-toxic and food safe.

  • Protection Level:

    • Provide minimal protection against scratches, heat, or liquid; less durable than other finishes.

    • Examples include enhanced oil-based finishes like Danish and Teak oils.

Danish Oil

  • Description:

    • A mix of oils and varnish providing both enhancement of wood color and durable, water-resistant satin finish.

    • Can serve as a primer for paint or varnish applications.

    • Food-safe post-curing.

Teak Oil

  • Usage:

    • Although not derived from teak, this oil is suitable for dense hardwood like teak, blending oils and varnish for protective qualities.

    • Excellent for both indoor and outdoor applications, providing UV protection.

  • Limitations:

    • Not ideal for high-sheen finishes or areas subject to heavy traffic.

    • Can hinder gluing if applied.

Pressure Treated Timber

  • Definition:

    • Timber treated with an antimicrobial copper-based preservative to ensure high-level protection against weathering, insects, and fungi.

  • Common Uses:

    • Frequently utilized in construction, landscaping, fencing, and playgrounds.

    • A common pressure treatment process known as tanalising is discussed.

Pressure Treatment Process

  • Described as a method that forces preservative chemicals into the wood using a pressurized treatment vessel.