Tung Oil and Polyurethane Mix – a Good Idea? Or a Waste of Time?

Woodcrafts / By

Wood rot is a vital decomposition process that is mainly caused by the combination of moisture and fungi. Other external elements such as water, biological components, UV rays, atmospheric changes, and the intrusive nature of wood-boring insects are all harmful as they break down wood over time. If left untreated and uncovered, wood will react with these elements and will eventually decay.

Keep in mind that simply putting wood in a safe dry place would not be enough to protect it from getting rotten, especially in furniture and floors, because humidity and fungi exist everywhere in the air and cannot be fully avoided unless there is a strong barrier between the air and the wood.

There are various materials to use to protect your wood for years to come such as oils and varnish. Tung oil and polyurethane are two of the most protective and durable materials of all, but each used alone has its drawbacks. So, would mixing tung oil and polyurethane cover their flaws and get a better result?

What Is Tung Oil?

Tung oil is a natural waterproof material that has proven its uniqueness centuries back in ancient China, where it first originated. It is a drying oil that hardens through a chemical reaction called direct polymerization to form a solid texture after exposure to air.

For a long period, back to 400 BC, tung oil has been the most preferred wood finish by true craftsmen due to its unparalleled qualities. Some of these qualities are merely practical ones, others are simply aesthetic. However, tung oil has some deficiencies that cannot be ignored.

What Is Polyurethane?

Polyurethane is a synthetic varnish that has been invented in the 1930s. It has two types: oil-based and water-based.

Oil-based polyurethane brings out the beauty of the wood as it gives it a shiny warm finish compared to the clear pale finish of water-based poly. Due to low solids in water-based poly, oil-based poly lasts longer and does not need additional coats as much. Accordingly, four coats of water-based poly may be needed as opposed to three coats of an oil-based poly. Moreover, oil-based poly is more affordable.

Polyurethane is a popular alternative to tung oil and other traditional wood finishes and is largely used and desired because of the strong protection it offers and the smooth comfortable layer it leaves on wood. Still, it cannot be barely used on wood because it is just a clear transparent coat.

Mixing Tung Oil with Polyurethane

Mixing drying oil, in this case, tung oil, with polyurethane creates a new and slightly different finish called “antique oil” finish, it actually resembles the results of applying Danish oil. This mixture gives your wood ultimate protection.

On the one hand, it protects it from the inside with the aid of tung oil’s strong penetration into wood fibers which supports it. On the other hand, it blocks out any external elements from the outside with the solid layer of polyurethane standing as a fence.

It also helps in concealing surface flaws and restores luster to dull finishes. Although there is no fixed formula, the guideline for mixing drying oil with polyurethane varnish is 1/3 varnish to 2/3 oil. The key to success in this process is to make sure that the oil has fully cured first to create a hard solid surface that allows stuff to stick to it, and add the polyurethane.

Now, concerning the following qualities: moisture resistance and protection, safety, processing time, texture, odor, color, and price; is it better to apply tung oil, polyurethane, or mix the two?

Moisture Resistance and Protection

Firstly, and most importantly: tung oil, unlike polyurethane, is not just a coat of material that protects the surface of the wood only. Rather, it permeates deep into the pores and fibers of the wood forming a bond with them from within once it is applied, and when it cures, it becomes an inseparable part of the wood.

This makes the wood immune to water, dirt, chemicals, and humidity to a certain level, but not strong enough to be used alone. Therefore, tung oil offers more protection as it strengthens the wood whereas polyurethane is more moisture resistant.

Consequently, applying polyurethane varnish over tung-oiled wood is more effective than applying extra coats of tung oil or polyurethane only. It is found that adding polyurethane, especially the oil-based one, offers a higher level of water resistance.

Safety

Secondly, tung oil does not contain any metals, additives, or distillates so it is eco-friendly. As for polyurethanes, water-based poly is slightly more eco-friendly than oil-based poly because it emits fewer VOCs, which are basically gases that include harmful chemicals.

Moreover, tung oil is food-safe, non-toxic, and inflammable material, which gives it vantage over other materials. Although polyurethane too is non-toxic, it’s not as good choice as tung oil for kitchenware. So, if you are thinking of waterproofing your wood kitchenware, you better use natural oils. Anyway, no finish is safe until it’s fully cured.

Processing Time

Thirdly, the issue of time: tung oil’s main problem is with time. Its penetration into the wood is very slow; to fully penetrate the wood, tung oil needs a minimum of 6 coats. Due to the slow process of penetration, each coat needs from 3 to 4 days to cure enough to allow another coat to be added.

So, it takes almost a month for a piece of furniture or a floor to be fully cured; therefore, it is a time-consuming process that many people may not have the privilege of.

As for polyurethane, it cures way faster than tung oil; it takes only a few hours. If you are in a hurry, water-based polyurethane is superior as it cures much faster than the oil-based one: two hours for a water-based poly coat to dry compared to 10-12 hours for an oil-based one. As a result, mixing polyurethane with tung oil can accelerate the processing time of applying tung oil a bit.

Texture

Moving to the texture of the finish after applying; in the case of tung oil, the texture stays rough because tung oil cannot smoothen the grain of the wood, rather it enhances it. So, if you like the natural touch of tree woods, this is your perfect choice, but it certainly is not the best finish for a house floor, daily used furniture, or commercial products.

On the contrary, polyurethane gives a mirror-like finish to the wood. Between oil-based and water-based poly, the oil-based one is better because of its rich solids that give an even more shiny and smoother look to the wood.

Odor

Concerning the smell, tung oil has a slightly unpleasant odor that comes from its naturally produced VOCs. Usually, it lasts for a few days, and up to a month, after it is applied and gradually fades away with time. It is not a bad smell, but it is a strong one that many would not like or would not be able to endure.

Polyurethane produces VOCs, and resales a similar odor as tung oil as well but not as strong. Fortunately, we have water-based poly which emits less VOCs and therefore less smell. If the tung oil is to be coated with some polyurethane, this unbearable smell of it while curing will no longer be noticeable and will diminish faster due to the fast process of applying water-based poly.

Color

As for aesthetics, tung oil does not only protect the wood, but also highlights its natural beauty as it gives a goldish-honey-like finish when applied to wood, and it will not turn pale or yellow over time.

It also provides a matte, non-oily look because of the bond it creates with wood pores that gives a natural finish, unlike other types of oil. You can mix it with polyurethane to avoid this dull finish because polyurethane, on the other hand, gives a glossy shiny finish. You can also tint your polyurethane before applying it if you want to give a color to your finish.

Price

Economically speaking, tung is expensive compared to polyurethane which is pocket-friendly. Also, water-based polyurethane would not be your best choice compared to its oil-based equivalent because of two reasons: it is expensive, and it needs more coats – 4-5 water-based poly coats compared to 2-3 oil-based ones– to give the same result as the oil-based one.

Moreover, applying additional coats every couple of years is needed for a lasting result. So, if you need to protect huge amounts of wood items, you better use polyurethane. And keep tung oil for kitchenware’s valuable antiques.

Final words

Polyurethane turned out to be the perfect match for tung oil as it solves almost all of its problems. Mixing tung oil with polyurethane, water-based or oil-based, is apparently a perfect idea practically, aesthetically, and economically, in both the long and the short terms.

Of course, it is noticed that tung oil and polyurethane varnish, whether singular or mixed, each has their strengths and weaknesses. Actually, this is not a bad thing, rather it is an extra that offers various options that each person can choose between according to their preferences.

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