Varnish is a clear or semi-transparent finish that is applied on wood to enhance its appearance and protect it from damage. It can provide a glossy, semi-glossy, or satin finish depending on the variety used. This finish is created through a mixture of resin, a drying oil, and a solvent. 

Unlike paint, which is designed to cover wood, varnish allows the beauty of the wood grain and patterns to show through, enhancing the natural beauty of your project. Some varnishes include a natural tone or colour top enhance the colour of the timber it is applied to. Some clear varnishes are designed to be applied to a painted surface for additional protection.

The primary purpose of varnish is to provide a protective layer for a timber surface. It creates a hard finish that can shield wood from scratches, stains, moisture, and damage from UV light. It's widely used in both interior and exterior settings, from wooden furniture to boats and outdoor structures to indoor timber furniture and door and window trim.

Varnish is an excellent option for furniture, door frames, timber floors or painted wood. Whether you're completing a woodworking project or protecting furniture, a coat of varnish can add durability and aesthetic value.

Is it oil based or water based?

Though many varnishes contain oils to assist in drying, varnish can be oil-based or water-based, with each type having its own advantages. Oil-based varnishes are durable, stand up well to heat and chemicals, and provide a beautiful, warm glow. They are often preferred for outdoor use due to their ability to withstand various weather conditions.

Water-based varnishes, on the other hand, are easy to clean up, dry faster, and are less likely to yellow over time. They're more environmentally friendly and emit fewer volatile organic compounds (VOCs), making them an excellent choice for indoor applications.

Choosing the right application method: brush, roller or sprayer…

The choice between applying varnish with a brush, roller or sprayer depends on the type of surface and your comfort level with each tool. For small or intricate pieces, a brush allows better control and precision. Larger, flat surfaces may benefit from the use of a roller, which can provide a faster, more uniform application. Larger furniture pieces or large areas like timber decking are perfect for spraying and there are many electric airless sprayers available that can handle varnish. 

When it comes to varnishing doors or furniture, the size and intricacy of the piece should guide your choice. Always remember to apply varnish in thin, even coats, regardless of the method you choose.

Applying varnish with a brush

The right brush can make a big difference when it comes to applying varnish. You'll want to choose a high-quality, natural-bristle brush. Synthetic brushes can sometimes leave streaks or bubbles in the varnish, while natural-bristle brushes tend to provide a smoother, more even application.

The size of the brush should match the size of your project. For example, a 5-8 centimetre brush is usually ideal for furniture or door varnish application. Remember to clean your brush thoroughly after each use to maintain its quality and extend its life.

Applying varnish with a roller

Rollers can be an efficient way to apply varnish to large, flat surfaces. They cover more area than a brush, and often do so more quickly. Rollers also tend to leave fewer visible brush strokes, resulting in a smoother finish.

When using a roller, it's important to use a small, high-density foam roller for the best results. These types of rollers will give a smooth, bubble-free finish. Load the roller with varnish and apply it in a "W" pattern for even coverage, and then smooth it out in straight, overlapping strokes. Be sure to apply thin coats and allow each to dry fully before applying the next.

Applying varnish with a sprayer

Using a sprayer to apply varnish can be a quick and convenient option, especially for large or complex surfaces. Spraying allows you to achieve a thin, even coat of varnish, and can often be done more quickly than brushing or rolling.

When using a sprayer, always ensure you're working in a well-ventilated area and wear appropriate safety equipment like a mask or respirator. Hold the spray gun about 30 centimetres away from the surface, and apply the varnish in even, sweeping motions. As with brushing or rolling, apply several thin coats rather than one thick coat, allowing each one to dry thoroughly in between.

Types of varnish

There's a variety of varnish types available, each with its unique properties and ideal use cases:

1. Polyurethane varnish: this is one of the most common types of varnish used in woodworking. It's incredibly durable and resistant to heat and chemicals, making it an excellent choice for surfaces that see a lot of wear and tear, such as kitchen tables or floors.
2. Spar varnish: named after its use on the spars of ships, spar varnish is a type of varnish that's exceptionally resistant to water, heat, and UV light. This makes it an ideal varnish for outdoor use.
3. Shellac: while technically not a varnish, shellac serves a similar purpose. It's a resin secreted by the female lac bug and is dissolved in alcohol. It creates a warm, deep finish that's excellent for antique furniture restoration.
4. Lacquer: Lacquer is a type of finish that dries upon solvent evaporation and then continues to cure as it reacts with oxygen in the air. This finish is incredibly hard and durable, providing a highly glossy finish.

Maintenance and care

Once you've applied varnish to your wooden surfaces, it's essential to maintain them to prolong their life and preserve their appearance. Avoid placing hot items directly on the surface and - for tables - use coasters to prevent water damage. Clean the surface regularly with a damp cloth and mild soap.

For surfaces with a heavy wear, like floors or tabletops, consider re-varnishing every few years to maintain the protective layer. When scratches or dings occur, you can often repair the varnish finish without having to strip and re-varnish the whole piece. Lightly sand the area and apply a new coat of varnish.

Safety precautions

Working with varnish requires some precautions. Always work in a well-ventilated area, as varnish fumes can be harmful if inhaled in large amounts. When sanding varnished surfaces, always wear a dust mask to avoid inhaling dust particles. If you're spraying varnish, consider using a full-face respirator to prevent varnish from getting into your eyes or mouth. Also, make sure to wear gloves to protect your skin from exposure to varnish.

Troubleshooting varnish problems

Despite best efforts, you might encounter problems when varnishing. Bubbles might appear in your finish, or it might not dry properly. Here are some common issues and how to solve them:

1. Bubbles in the finish: these often result from shaking the varnish before application, using a roller or brush too aggressively, or applying a coat too thick. To avoid this, stir the varnish gently before use, apply thin coats, and avoid overworking the varnish once it's on the surface.
2. Varnish not drying: this can be due to high humidity, low temperatures, or applying too thick of a coat. Ensure the environment is suitable for varnishing (ideally, a temperature of 20-25 degrees celsius and a relative humidity below 80%) and remember to apply thin coats.

Conclusion

In conclusion, using varnish is an art that requires patience and precision. It's a protective and decorative finish that enhances the natural beauty of wood. Whether you're a professional painters, woodworker or a DIY enthusiast, understanding the properties, types, applications, and troubleshooting aspects of varnish can help you achieve the best possible results. A well-varnished deck, door trim or piece of furniture is something to be proud of and can last for generations if properly cared for.