Varnish is a protective finish for wooden surfaces, offering durability and aesthetics. If you want to know about this finish, read on as I walk you through its types, application techniques, and tips to help you achieve professional-grade results for your woodworking projects.
What Are the Different Types of Varnish?
Varnish originated from a blend of sap (resin) and alcohol (solvent). Today, numerous varnish variations cater to diverse needs. Crafting new varnishes involves adjusting resin, solvent, and oil proportions.
This leads to a range of types, each with distinct traits. Let’s explore the primary varnish types and their unique characteristics.
Spar Varnish
A spar, often wooden, provides sturdy support for a ship’s sail. Spar varnish, also called yacht varnish, safeguards vulnerable wooden ship parts from weather-induced harm.
Traditionally, it was flexible but less enduring due to its purpose. Yet, contemporary versions prioritize durability, UV resistance, and aesthetics, improving their overall performance and appearance.
Exterior Varnish
Exterior varnish, also known as spar urethane, is an upgraded version of traditional spar varnish. While similar in flexibility and protection, it stands out for its enhanced durability and UV resistance due to a slower curing process.
This modernized variant ensures lasting safeguarding for outdoor wooden surfaces, making it one of my go-to choices in my projects.
Alkyd Varnish
Alkyd varnish, highly adaptable for indoor and outdoor use, is formulated with alkyd resins—polyester resins modified with fatty acids, often from vegetable oil.
This type of varnish provides efficient UV defense, fast drying, and lasting durability, while its transparent finish beautifully amplifies the wood’s natural charm.
Bituminous Varnish
Bituminous varnish, also known as black varnish, is a protective coating made by substituting resins with bitumen, a petroleum-derived hydrocarbon.
Primarily used to safeguard ironwork, its main role is to shield against corrosion, ensuring prolonged structural integrity. This specialized varnish plays a crucial role in preserving metal surfaces.
Acrylic Varnish
Acrylic varnish, a water-based protective layer, stands apart from conventional varnishes. Its transparency, ease of application, and resistance to yellowing make it ideal for safeguarding paintings.
Applied over the artwork, it serves as a dependable shield, preserving the piece’s integrity while retaining its clarity and vibrancy.
Oil Varnish
While its classification as a genuine varnish is open to debate, oil varnish is commonly labeled as one.
Comprising resin and drying oil without a solvent creates a finish that deeply infiltrates wood, gradually solidifying over an extended duration.
This method imparts durability, often earning it the name “oil varnish” despite its unique composition.
Spirit Varnish
Much like oil varnish, the classification of spirit varnish as a true varnish is a matter of discussion. While oil varnish combines resin and drying oil sans solvent, spirit varnish blends resin with a solvent instead of oil.
Quick-drying and easily polished, it lacks the durability of oil varnish, making it a distinct choice in protective finishes.
What Are the Disadvantages of Using Varnish?
Varnish, a popular protective coating in various applications, offers a plethora of benefits, from enhancing aesthetics to providing durability.
However, like any product, it also comes with its own set of disadvantages that need careful consideration.
Yellowing and Discoloration
One of the primary drawbacks associated with varnish use is its tendency to yellow and discolor over time, especially when exposed to sunlight or UV rays.
This phenomenon, known as “yellowing,” can alter the original color of the underlying material, affecting its visual appeal.
This drawback is particularly noticeable in certain types of varnishes, such as oil-based ones.
Difficult Repairs and Maintenance
Now, I’m all for things that age gracefully and can handle a little wear and tear. But here’s the kicker with varnish: when the varnished surface becomes damaged or worn, repairing it can be a challenging task.
Unlike some other finishes that can be easily touched up or spot-repaired, varnish often requires a complete stripping and reapplication process for effective restoration.
This can be time-consuming and labor-intensive, making maintenance more complex.
Brittleness and Cracking
Varnishes, especially older or improperly applied ones, can become brittle over time due to changes in temperature and humidity.
This can lead to the formation of cracks on the surface, compromising the protection provided by the varnish. To prevent this, I always advise maintaining a stable environment.
Incompatibility With Certain Substrates
In my line of work, I’ve learned that varnish isn’t a one-size-fits-all solution. Some substrates, like plastics and certain metals, may not effectively bond with varnish, leading to poor adhesion and premature peeling or flaking.
Proper surface preparation and selection of compatible varnish types are essential to avoid adhesion issues.
Strong Odor and Harmful Chemicals
Certain varnishes, especially solvent-based ones, emit strong fumes and odors during application and drying.
These fumes can be harmful if inhaled in large quantities, making proper ventilation and protective gear necessary when working with varnish.
Additionally, some varnishes contain volatile organic compounds (VOCs) [1] that contribute to air pollution and environmental harm.
How to Use Varnish?
Using varnish effectively involves a systematic process to ensure optimal results. First, prepare the surface by sanding it smooth and ensuring it’s free from dust and debris.
Select the appropriate varnish type based on the project’s requirements and the material you’re working with. Apply the varnish in a well-ventilated area, preferably with low humidity, to prevent drying issues.
Use a high-quality brush or sprayer for an even application, working in the direction of the grain. Apply thin coats and allow each layer to fully dry before moving on to the next coats.
Also, sand between coats to promote adhesion. The number of coats depends on the desired level of protection and sheen.
After the final coat, allow the varnish to cure according to the manufacturer’s instructions, which can take several days to weeks. Keep the workspace dust-free during the curing process. Once cured, the varnish will provide a durable and protective finish.
Lastly, I can’t overstate this: respect the disposal process. Those brushes and containers aren’t just regular trash; they need to be treated with care, considering the chemicals involved. Treat them with the same respect you’d give to any hazardous material, because that’s exactly what they are.
When to Replace Varnish?
Replacing varnish is necessary when the existing finish starts to show signs of wear, degradation, or loss of protective properties. If the varnish becomes cracked, brittle, or develops areas of peeling, it’s time for renewal.
I keep a keen eye on any dullness, discoloration, or if it seems like water isn’t beading on the surface anymore. These are all tell-tale signs it’s time to give that piece a new coat of armor.
Regular inspections of the varnished surface can help identify these indications, and proactive replacement will ensure the longevity and continued quality of the protected material.
Conclusion
Understanding varnish is pivotal for achieving lasting and visually appealing woodworking projects.
With various types available, each offering distinct attributes, selecting the right varnish and applying it correctly enhances wood protection and elevates its aesthetics. Mastering varnish applications ensures the longevity and beauty of your creations.
Robert Johnson is a passionate furniture maker & carpenter, sought after for his knowledge on the craft.
You’ve probably seen his down-to-earth wisdom in USA Today, Bobvila, Family Handyman, and The Spruce, where he has shared commentary and guidance on various woodworking topics.
Robert is the brain behind Sawinery, where he aims to share tips, tricks, and a passion for all things carpentry.
