If you’re a DIY enthusiast or a woodworking professional, you might wonder if tung oil goes bad over time. Like any other oil-based product, tung oil can degrade over time and lose its effectiveness.
In this article, we’ll explain its shelf life, signs of rancidity, and how to properly store tung oil to ensure its longevity to help you achieve the perfect finish.
Know More About Tung Oil: Uses and Benefits
Pure tung oil is a drying oil that comes from the seeds of the tung tree (Vernicia fordii), which is native to China. The oil has been used for centuries as a protective finish for wood and other surfaces, and it is valued for its durability, water resistance, and beautiful natural sheen.
Tung oil can be used as a finish for various surfaces, including wood, concrete, stone, and metal. It is often used to seal and protect indoor furniture, floors, and outdoor structures like decks and fences. Tung oil can also be used to finish musical instruments.
Does Tung Oil Get Old and Go Bad?
Tung oil can get old and deteriorate over time, especially if not stored properly. Tung oil can oxidize and thicken when exposed to outside air and light, making it more challenging to apply and affecting the final finish.
Tung oil has a longer shelf life when stored in the dark than if exposed to light. However, even when stored in a tight-lid can and in a cool, dark place, tung oil can still go bad over time if not used within a certain period.
The shelf life or exact timeframe for how long tung oil can last before going bad will depend on other elements, such as the quality and purity of the oil, the storage, and the environment.
How Can You Tell If Tung Oil Is Bad?
Put some Tung oil on the very end of a glass or plastic laminate. Check the drying time after tilting it at a 45-degree angle. Tung oil is suitable for usage if it dries completely within four to six hours. Tung oil has gone bad if it doesn’t dry within 12 to 24 hours.
One of the most apparent signs that tung oil has gone bad is a rancid smell. Another sign that tung oil has gone bad is thickening and becoming more challenging to apply as wood finishing.
Unlike Danish oil, tung oil doesn’t darken the wood, but discoloration can also indicate that tung oil has gone bad. If you notice any of these signs, it is essential to dispose of it properly and replace it with fresh oil for the best results.
Will Tung Oil Get Rancid Over Time?
DIYers love Tung oil since it’s more stable than other oil finishes and will not become rancid due to its high content of polyunsaturated fatty acids.
However, it is essential to note that tung oil does go bad if it is not stored correctly or mixed with other oils or chemicals that can cause it to break down.
How Long Can You Store Tung Oil?
Tung oil, if left unopened, can be kept for decades. You can keep Tung oil for two to three years after it has been opened so long as the oxygen level is kept to a minimum during storage.
However, the oil would oxidize in the open air and spoil in a matter of two to three months if not kept in an airtight container or not properly stored.
Pure vs Dark Tung Oil
Pure tung oil is a natural oil extracted from the nuts of the tung tree. It is a clear, transparent oil used for centuries as a wood finish. It is typically used on lighter-colored woods to highlight the wood’s natural grain.
Dark tung oil, on the other hand, is a type of tung oil mixed with a natural pigment to create a darker, richer color. The pigment is typically derived from iron oxide, which gives the oil its characteristic deep brown hue.
You can use it on darker-colored woods where it can complement the natural color of the wood.
Common Problems With Bad Tung Oil
Blotchiness and Bubbles
If it has gone rancid may have become too hard to penetrate the surface, leaving behind ugly bubbles and imperfections. Get a fresh batch of tung oil and use solvents to clean the area.
Tung oil can cause wood finishing irregularities if not used properly. You can use Mineral spirits to clean the region before applying fresh tung oil, which should be involved precisely.
A coating dries typically in 8 to 12 hours, but it could remain tacky for weeks if it is rancid or impure. In this case, wipe down the area with mineral spirit and begin using a fresh batch while following the manufacturer’s guidelines.
Tips To Prevent Tung Oil From Going Bad
Keeping Tung Oil In A Sealed Air-Free Container
To keep tung oil fresh, store it in a sealed, air-free jar to protect it from air exposure, which can cause it to oxidize and degrade. It’s best not to use a large container.
Storing Tung Oil In A Cool, Dry Place
Stop tung oil from going bad by storing it in cool temperatures and low moisture levels, which can help slow the oxidation process. Store in a location with temperature variations of 60-7°F (15-21°C) and a relative moisture level of 40-50%.
Pouring It Into A Smaller Container
When you use a large tung oil container with a firm lid, it is exposed to more air, which can cause it to oxidize and degrade more quickly. Therefore, pouring it into an appropriately sealed small jar can help minimize its air exposure and slow the oxidation process.
Crushing Tung Oil Can
Prevent too much air from penetrating the Tung oil can, and to increase the oil level within, gently compress the can’s corners. If you do it well, the can will look nearly filled, and the air within will decrease.
Filling Tung Oil Can with Pebbles
When the tung oil has been used; you can maintain the can full of marbles or aquarium pebbles. The stones will act as a barrier, preventing outside air from entering the can.
Adding Shielding Gas or Bloxygen
Adding an inert gas, shielding gas, or Bloxygen to a tung oil jar can effectively prevent tung oil from going bad by reducing the air and oxygen that comes into contact with the oil.
Removing Air From The Tung Oil Can
One way to remove air from the tung oil can is to use a vacuum or specialized can sealer. These tools are designed to create a seal around the jar, which removes air from the can and helps to prevent the oil from coming into contact with the air.
How to Use Tung Oil
Step #1: Cleaning the Surface
Before applying tung oil, sanding or stripping the wood to get rid of any dirt and existing coats, and cleaning the surface is essential. Before you use tung oil, make sure the surface is clean.
Step #2: Thinning the Oil
To thin the tung oil, pour a small amount into a clean, dry container. Add a small amount of the thinner or solvent to the oil, typically in a ratio of 1:1 or 2:1 (oil to thinner). Mix thoroughly using a clean stir stick or brush until well blended.
Step #3: Applying the First Coat
Saturating the surface well before applying the first layer ensures that subsequent coats will adhere. You must use a paintbrush or lint-free cloths to dab tung oil from one container into another, then put a generous first layer.
Step #4: Applying Subsequent Layers
Like varnish, you have to allow plenty of time for the first coat to dry before you apply subsequent coats. Depending on the temperature and humidity, the first coat may take 12 to 24 hours to dry completely.
Step #5: Removing Unabsorbed Tung Off the Surface
The unabsorbed oil can be cleaned from the wood using a mild solvent like acetone. The remaining oil on the wood will be improved by this process, making it more smooth and shiny. Tung oil dries slowly, especially in thick layers.
Step #6: Letting the Oil Cure (Up to 30 Days)
Tung oil makes the wood’s surface self-healing, but it needs to dry for at least 30 days before using it.
Step #7: Cleaning the Surface and Reapplying for More Protection
Don’t expose the surface to direct sunlight. After giving the tung oil time to cure, you can wipe away dust with water and a mild soap mixture using a soft towel. If you want a finish lasting for years, apply tung oil periodically.
How Long Can Tung Oil Last on Wood? How About Outdoors?
On wood, tung oil has an approximate 2-year lifespan with adequate care and maintenance but only a 1-year lifespan in the great outdoors.
Tung oil, applied to wood once a year, protects against moisture and other environmental hazards while bringing out the wood’s natural sheen and luster.
Advantages of Tung Oil
Eco-friendly, non-toxic, and non-carcinogenic are the top benefits of Pure tung oil, which makes it a popular choice for finishing wood surfaces that come into contact with food or people, such as cutting boards, kitchen countertops, and kid’s toys.
It is commonly used as a finish for wood and other porous surfaces to shield them from water damage. When applied and allowed to dry, it can create a rigid, protective layer that can resist water and other liquids to some extent.
Easy to Apply
Tung oil is easy to apply with a brush, rag, or sprayer. It dries slowly, which allows it to penetrate deeply into the wood and create a strong bond.
Tung oil is generally considered food safe once fully cured, which can take several weeks. To ensure that tung oil is safe, it is essential to use a pure, high-quality product tested and certified for food safety. You can also use boiled linseed oil as an alternative.
Acid and Alcohol Resistant
Tung oil is highly resistant to acids and alcohols, making it a good choice for use on surfaces that are likely to come into contact with these substances, such as bar tops, kitchen counters, and laboratory work surfaces.
Attractive in Color
Tung oil is known for its ability to enhance the natural beauty of wood and other porous surfaces, and it is often chosen for its stunning color. It produces a slightly amber or honey-colored hue that is highly desirable for many applications.
Tung oil is suitable for a natural, durable, easy-to-maintain finish for wood and other porous surfaces. There’s no need to dilute tung oil with anything else; you can directly grease the paint tray or timber.
Doesn’t Yellow Over Time
Tung oil contains many unsaturated fatty acids  that do not react with oxygen like others, preventing the finish from yellowing over time.
Disadvantages of Tung Oil
Slow to Penetrate
Tung oil can penetrate certain materials, such as dense hardwoods or non-porous surfaces like metal or plastic. This can make the application process more time-consuming and require multiple coats to achieve the desired finish.
Tung oil can sometimes leave a white or milky tinge on the surface of the wood or other porous material, mainly if it is applied too thickly or in humid conditions. It is typically a temporary effect that can be avoided with proper application techniques and controlled conditions.
Difficult to Store
Tung oil can be difficult to store for extended periods, as it is prone to contamination issues, and oxidation and can become thick and gummy over time. It is a property common to many natural finishes and can be managed with proper storage and handling techniques.
Long Processing Time
Tung oil can have a lengthy processing time, meaning applying and drying takes a while. To minimize the processing time, spreading thin, even coats and using a fan or other ventilation system to increase air inside and reduce moisture or outside air in the area is essential.
The odor of tung oil is caused by its natural compounds that emit a strong and somewhat musty scent.
Tung oil can be relatively expensive compared to other wood finishes and oils on the market. This is partly due to the fact that it is a natural and sustainable product produced in limited quantities, which can drive up the cost.
Doesn’t Smoothen Wood Grain
Tung oil finish doesn’t necessarily smooth out or fill in the grain of the wood surface when applied. In some cases, it may be better to use additional techniques or products to fill in the grain or create a more even surface before applying the tung oil.
Can You Paint Over Tung Oil?
Tung oil is suitable for painting over. First, use water and soap to clean the area. After that, sanding it down slightly, removing dirt or debris, and priming it is essential. You can also add varnish for an opaque look.
Tung oil does go bad if not stored correctly or if not properly sealed or exposed to light, heat, and air for an extended period. It can compromise the quality and effectiveness of the wood finish, so it’s essential to check for signs of spoilage before using it.
If you suspect that your tung oil has gone bad, it’s best to discard it and purchase a new can.
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