Can You Polyurethane over Tung Oil? Our Investigation

Woodcrafts / By

Tung oil and polyurethane varnish are top players when it comes to wooden finishes. From moisture resistance to general protection, these finishes do woodwork projects a lot of good.

Hence, you are probably considering using both finishes. Surely, if there are lots of advantages to each, combining them should cause no harm. This is correct.

Polyurethane and tung oil can indeed be a good pair but again, you should use them correctly.

We found out that you can do more for your wooden surface after applying tung oil. Having polyurethane finish over tung oil is a fascinating idea to help you enjoy the benefits of both products. As always, proper application matters to get the best results and you will learn all that here.

Before that, it helps to understand some peculiar differences between both finishes. This knowledge will guide you to use polyurethane and tung oil correctly.

How Do Polyurethane and Tung Oil Differ?

The most obvious difference is that polyurethane is a synthetic finish while tung oil is a natural one. Polyurethane combines resin solvents and other chemicals, which means it has more additives than tung oil.

In the area of use, Tung oil is mostly used indoors as a wood decor to achieve a glossy finish and protect the wood. Polyurethane contains protective properties too but is more common for its sealing abilities. It’s the ideal finish to protect the wood from moisture damage.

Tung oil penetrates better compared to polyurethane which sits on the surface. This gives you a picture of why using polyurethane over tung oil will work. Tung oil soaks the wood grain so having polyurethane as the top layer is ideal.

Similarly, polyurethane is harder and repels moisture so having it over tung oil protects the wood surface from dents and scratches. Both finishes are easy to maintain but polyurethane is even more since it is moisture-resistant and you can easily wipe off stains.

Should You Refinish with Polyurethane Over Tung Oil?

Tung oil is a great finish for woodworking projects, but by itself, it does little to protect the wood surface from water damage, dents, or scratches. This is where a layer of polyurethane becomes necessary.

Polyurethane produces a tough long-lasting coating that makes cleaning the wood easy.

Especially for high-traffic surfaces, a durable varnish like polyurethane does a lot to keep the material free from damage. Luckily, tung oil is very receptive and pairs with any finish to create a durable surface.

How Do You Apply Polyurethane Over Tung Oil?

As already established, polyurethane can pair with tung oil to create a tougher and more protective wood surface. But you have to do it right. Prepare to spend weeks on the project since the tung oil might take a long time to dry.

Here are the materials to make available for your project to go smoothly:

  • Bristle brush
  • Sandpaper
  • Power sander
  • Stirring stick
  • Lint-free cloths
  • Steel wool
  • Polyurethane
  • Tung oil

Application Procedure

Step 1: Check That the Work Area is Safe

You shouldn’t miss the step for your safety and to speed up drying time. Oil-based polyurethane emits fumes that can trigger or worsen allergies. Ensure your workstation has enough airflow and you are wearing the necessary safety gear.

Consider lining the floor with drop cloths to avoid a mess from spilled oil.

Step 2: Prepare the Material

If you are refinishing, working on a clean surface is important. Strip old existing paint from the material and sand if necessary. You want to get rid of dust that can stick beneath the tung oil.

Use the power sander to remove imperfections if you working on natural wood.

Step 3: Apply the Tung Oil

Pour the oil directly on the wood and use the lint-free cloth to rub it into the wood. You want the wood to soak as much oil so wait for a few minutes for this to happen.

Wipe off the excess oil and allow the surface to dry. This can take days, especially if you are using pure tung oil.

Go in with the second coat after the first dries, following the same application method. You may use sandpaper to work the oil in so it penetrates better while staying smooth.

Apply as many coats as you wish until you have achieved the desired sheen. The more layers of tung oil you apply, the richer color you get.

Step 4: Allow the Tung Oil Cure

Ensure the oil is fully dried even if that means waiting for weeks or more. Press a finger on a hidden spot of the material to see if the surface is firm enough and leaves no film.

Clean the oiled surface with a lint-free rag to get rid of dust so that the polyurethane adheres properly.

Step 5: Prepare the Polyurethane

Open the polyurethane container and gently stir its content with the stirring stick. Make sure the stick reaches the bottom for proper mixing. Manufacturers often advise against shaking polyurethane to prevent bubbles that give you an extra sanding job.

You can thin the initial coat with mineral spirit to increase its workability.

Step 6: Apply the Polyurethane and Leave to Cure

Evenly coat the wood surface with polyurethane using a brush or lint-free cloth. It’s best to begin with a thin layer. You can use a scrub sponge too.

Sand the surface after the first coat dries, wipe the dust away and apply the next coat. There is no need to sand again after the final coat.

The final step is to allow the polyurethane cure for as long as is necessary. This could run into weeks or months. Also, remember to keep the finished work in a ventilated area to contain the gas smell.

Will Water-based Polyurethane Over Tung Oil Work?

Yes, you can use water-based polyurethane over tung oil. As with oil-based polyurethane, you have to let the oiled surface cure fully before applying the polyurethane. You will be layering both products, not mixing them so the oil and water debate doesn’t exactly apply here.

To make the polyurethane adhere well, apply shellac on the oiled surface before going in with the water-based varnish.

How Long Should You Wait Before Applying Polyurethane?

You can apply polyurethane over tung oil once it dries. This usually takes at least a full day or more. Tung oil requires a longer period to fully cure but you won’t have to wait that long. Apply the polyurethane as soon as the oiled surface no longer feels tacky.

Tung oil comes in pure and oil/varnish blend variants. The type you use dictates how long you will have to wait before applying the polyurethane. Pure tung oil takes 1-3 days between coats to dry and a few minutes, for the modified variant.

Here are some other factors that affect drying time:

  • Temperature: Your workspace’s temperature influences the oil’s drying time. A temperature below 60 degrees can stretch drying time and make the tung oil sticky.
  • Oil’s consistency: Consider thinning the oil before applying it to speed up drying time. The thicker its consistency, the longer it takes to dry.
  • The number of coats: More coats increase the drying time of tung oil. Despite this, properly cover the surface with enough oil
  • Humidity: High-moisture levels can double the drying time of tung oil. Humidity is higher in cold weather conditions so choose the right time to work on the project.
  • Air circulation: An increased airflow in the area speeds up tung oil’s drying time. Likewise, poor ventilation can make the surface dry slowly.

How Do You Know When The Tung Oil is Dry Enough?

Allowing the tung oil to dry properly before applying polyurethane is an important step that can affect the outcome of your project.

Here are some signs to look out for to ensure the tung oil is dry enough:

  • Reduced Odor

Tung oil has an odor when wet. Once you can no longer perceive it, that may be a sign that the surface is ready to take the polyurethane. The oil evaporates when dry, leading to a reduced smell.

  • Glossy appearance

The wood surface becomes glossy when the tung oil is fully dry. Otherwise, it maintains a wet appearance.

  • Moisture-resistant

Dried tung oil repels moisture. Try sprinkling some water on the surface to see if it penetrates the wood.

  • Withstands Sanding

So long as the surface is firm enough to withstand sanding, it can take polyurethane. Sand an inconspicuous part of the wood as a test to see if the sandpaper moves freely.

Conclusion

Now you know it is possible to seal tung oil with polyurethane. Remember the most important condition for this to go well is that you allow the oiled surface fully dry. Feel free to merge both products for your next project to enjoy their combined benefits.

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