How to Apply Varnish

Varnish is notoriously difficult to apply, but when done correctly, provides a beautiful and long-lasting finish. In this article, I’ll not only cover the different kinds of varnish, but also give you step-by-step instructions on how to apply it for the best results. I’ll also review the differences between shellac, varnish, and lacquer. 

What Type of Varnish Should I Apply?

Varnishes consist of three ingredients; a resin for barrier protection, an oil for conditioning, and a solvent for spreadability. You can mix your own varnish, or buy prepared varnish in the store. Additional solvent is generally added during the early application process to create a thinner seal coat. 

Types of Varnish Resin

Different resins have different properties, which make them more or less suited to certain applications. Here’s a brief run-down. 

Polyurethane Resin

Extremely durable and protective, polyurethane based varnish is practically indestructible. However, it has a plasticy sheen that can distract from the grain of the wood or make it look cheap. 

Alkyd Resin

This is the most common resin base for varnish. It is excellent for indoor use, although it can be used outdoors as well. Versatile and easy to find in home improvement centers, this varnish is perfect for almost all applications. 

Phenolic Resin

Once the most popular resin base, varnishes made with phenolic resin have fallen out of favor. The reason for this is yellowing. When exposed to UV rays, the resin takes on a significantly yellow cast. If that enhances your wood, phenolic resins can be a great choice. If you’d prefer to skip the yellow tint, choose a varnish with a different resin base. 

Types of Varnish Oil

There are three types of oil commonly used in varnish. 

Tung Oil 

Tung oil protects against moisture better than any other varnish. Choose a formulation with tung oil when you need to protect wood exposed directly to water. Wooden boat accents are almost always finished with tung oil.

Linseed Oil

This oil is similar to tung oil, but doesn’t perform quite as well. Varnishes that include linseed oil will be slightly softer, less durable, and more vulnerable to water than those that include tung oil. However, linseed oil varnishes are significantly less expensive than tung oil, so if your workpiece won’t be taking a weather-related being, linseed oil is probably fine. 

Modified Soybean Oil

If you want a completely clear coat of varnish, look for versions that use alkyd resin with modified soybean oil. Minor yellowing can still happen, but the effect should be much less noticeable. 

How to Apply Varnish

Once you’ve selected the specific type of varnish for your project, here are the steps for applying it.

1. Choose your workspace carefully. Varnish is sticky. Anything in the air will stick to the varnish. This means dust, sawdust, dirt, and even insects can all end up varnished into your workpiece. To avoid this, work inside, in a clean and well-ventilated area. If that’s not possible, try to find an area outside that is not close to patches of bare dirt and is sheltered from the wind. 
2. Sand with the grain of the wood. Varnish doesn’t adhere well to completely smooth surfaces. A bit of roughness is required to get a firm bond. Sand the entire workpiece with very fine-grain sandpaper. You should sand in the direction of the wood — not back and forth. 
3. Clean the wood with a tack cloth. A tack cloth is a sheet of cheesecloth, loosely woven and coated with beeswax. The result is a soft, slightly sticky fabric that will pick up any sawdust clinging to the wood.  
4. Lay the wood flat. Try to avoid varnishing vertically whenever possible, as drips and runs in the material will affect the finish. If vertical varnishing is a must, use drop cloths and plastic sheeting to protect the area underneath where the varnish will be applied. 
5. Thin the varnish for the seal coat. Start with choosing a clean container. Tupperware containers with lids are great for storing extra mixed varnish between coats. Make a mixture that is 50% varnish, 50% solvent. Be careful when stirring so as not to introduce air bubbles into the varnish. Never shake a varnish can. 
6. Load the brush with varnish. Using a natural bristle brush, dip an inch or so into the varnish and allow the brush to absorb the liquid. Gently tap the brush against the rim of your container, but do not wipe the brush on the edge. The brush should feel laden but not heavy. It should be wet, but not dripping. 

7. Apply the seal coat. Work in small areas. The first brushstrokes in each area should be against the grain. Immediately recover the same area, this time brushing with the grain. This helps ensure adequate coverage and penetration. 
8. Allow the seal coat to dry. Shield your workpiece from direct sunlight during the drying process, as the sun will make it dry too quickly. Most varnishes need about 24 hours to cure or harden. In imperfect weather conditions, it can take much longer. Varnish that is completely dry will not feel gummy or soft when sanding. 
9. Sand and wipe the workpiece. Still working in the direction of the wood grain, sand the entire piece. This provides the right texture for the next layer of varnish to grab onto. Wipe it with a tack cloth to remove any particulates. 
10. Apply another layer of varnish and wait for it to dry. This time, use full-thickness varnish. Brush it on to the wood, following the grain. If your varnish is too thick to spread properly, you can thin it until it’s easier to work with. Note that if you thin the varnish, you may need to apply more coats to reach your desired thickness. 
11. Add additional varnish layers. Repeat steps nine and ten until you have achieved your desired finish. If dust, dirt, bugs or bubbles get caught in your varnish, resist the urge to try to remove them during the application or drying process. Instead, wait until the layer is dry, then remove the debris using sandpaper. 

Tips for Working With Varnish

• Don’t buy more than you need. Varnish has a shelf life of about 3 years if stored properly. Proper storage means finding a cool, dry location that is not exposed to direct sunlight. 
• Don’t mix more than you need. Once exposed to oxygen, varnish will start to cure. Cover your mixture during drying periods. If you’re storing an opened can of varnish, pour mineral spirits on to the surface of the varnish, but don’t mix. This will serve as a barrier and keep the varnish from curing in the can. 
• Dispose of it properly. Liquid varnish can sometimes be turned in at your local refuse or recycling center. If not, brush it all out onto cardboard or scrap wood and wait for it to cure. Uncured varnish is an environmental hazard that can leach into the soil, so never throw away varnish that is still in its liquid form. 
• Use a light brushstroke. Only the tip of your brush should bend. 
• Eliminate bubbles and brushstrokes by ‘tipping off’. Use just the tip of your brush, held at a 90 degree angle, to smooth out any bubbles or visible brushstrokes.

Varnish, Lacquer, and Shellac — What’s the Difference? 

All three terms refer to a viscous liquid used to protect wood. These protective coatings are generally brushed on, although spray versions are sometimes available. Which one is right for your project? 

• Shellac comes from a resinous secretion of the lac beetle. It provides a high-gloss mirror finish and enhances the grain and color of the wood. It offers some protection against heat and moisture, but should only be used indoors. While it will protect the wood from developing small scratches and dents with use, it can’t stand up to heavy traffic. 
• Lacquer is an extremely hard, durable, and long-lasting protective coat. The glossiness of the finish depends on the formulation of the lacquer. It is best known for producing an intense, high-gloss shine, but matte lacquers are available, too. Lacquer is only meant for indoor use though.
• Varnish gives you the best of both worlds – it lasts longer than shellac and protects as well as lacquer. You will need to replace it more often than lacquer, but the visual results are worth it. Varnished wood has a depth of color and grain that is highly distinctive. Varnish also is the finish of choice for outdoor projects.

Conclusion

Varnish is a liquid protective coat that is applied to wood. It consists of a resin and an oil, and is thinned using a solvent. The types of resins and oils used affects the outcome of the varnishing project, so keep your project goals in mind when making your varnish selection.  

Sanding the surface of the workpiece improves the bond of the varnish to the wood. Make sure to keep your workpiece and work area as dust-free as possible. The first coat should be a 50/50 varnish/solvent mixture. This will seal the wood and act as a base. 

Subsequent coats build the thickness of the varnish. Between each coat, allow the previous layer of varnish to dry completely. Then, lightly sand the piece and wipe with a tack cloth before adding another coat. Stop when you’ve reached your desired level of protection.