Tung oil is a very tricky finish to apply on wood. It takes a long time to dry, and it’s prone to being tacky or gummy. When that happens, the best solution is to remove the old finish and re-apply another coating. But to do this, you should know the proper steps in removing gummy tung oil finish to avoid ruining the wood material.
Below, I’ve outlined simple steps that every woodworker can use. Read each step carefully and prepare all the needed materials before starting the finish removal.
Why do tung oil finishes become gummy?
Before we head down to the procedure, I think it’s crucial for woodworkers to know why tung oil becomes gummy.
First of all, tung oil is a natural drying oil. It’s similar to linseed, which is also used to treat and seal the wood. It requires oxygen exposure to harden and cure properly.
Once it hardened, tung oil will protect the wood against various elements. It has topnotch water resistance as well as a food-safe characteristic as long as it’s not thinned.
However, as the tung oil finish gets exposed to various elements, it will start to change chemically. In fact, chemical reactions on oil finishes never really stop after curing. It just slows down, so you don’t really perceive it with a mere touch or visual inspection.
After a few years or decades, the tung oil finish would have changed dramatically compared to its initial quality. It will become gummy and sticky, which is far from its solid and smooth characteristic after curing. The exception is if the tung oil has been thinned or mixed with polymers. In that case, the finish is unlikely to become gummy.
Being gummy is just a natural reaction, and most oil finishes will manifest the same. And if you applied too many layers, the tung oil would become sticky faster than usual.
By this time, you’ll need to strip the old finish and apply a fresh coat. Below, I discussed the simple steps you can do.
How to remove gummy tung oil from wood
Step 1. Apply turpentine to a test spot
When it comes to removing tung oil finishes from old furniture, you have to be careful. First, you should perform a spot test to ensure that the method won’t damage the wood material.
To start, choose a hidden spot and saturate it with turpentine. You can also use other thinners, but try to look for low-VOC types.
Let the turpentine bubble. This means that the thinner is already reacting with the tung oil finish. Depending on how hard the tung oil coating is, it may take some time to bubble up.
Step 2. Scrape with fine steel wool
Once the test spot is bubbling with turpentine, the next step is to sand it with fine steel wool. Your goal here is to help the turpentine remove the oil by lifting it off the wood material. Remember that you only need to perform light scrubbing to avoid making the wood material rough.
Also, the fine steel wool will help press the thinner into the wood. This will allow the turpentine to penetrate the wood pores where more tung oil is absorbed.
Step 3. Apply the first two steps on the entire wood
If the first two steps didn’t damage the test spot on the wood, you could apply it to the entire material. I suggest working on small areas at once, so you can control the result.
In case you’re dealing with hard tung oil, you can swap the fine steel wool with high-grit sandpaper.
Step 4. Wipe and clean
Once you’re done removing the tung oil finish, wipe the wood using a clean, lint-free cloth. Make sure that you remove all the excess thinner.
Also, it will help to let the wood dry before applying the fresh coat of tung oil. You can also sand it one more time, but be gentle and just aim to get a thin layer removed to allow the new coat to adhere well.
Step 5. Re-apply the thinner if necessary
If there’s still tung oil left on the wood, you can re-apply more solvent and scrub it with fine steel wool. Always work on a well-ventilated area as thinners release volatile organic compounds that’s harmful when inhaled.
Tips to avoid gummy tung oil finish
If the gummy finish is the result of improper curing, here are some tips that will help prevent the problem from recurring:
- Keep each coat thin. One way to prevent your gummy finish from being gummy or sticky is to keep each coating thin. After that, let the coating dry before applying another. A very thick layer of tung oil won’t cure properly as a large amount remain suspended on the wood surface.
- Control humidity. Keeping the humidity levels low to normal is the key to fast and proper curing of tung oil. This will help a lot if you keep getting gummy finishes. A warm area will also be a good choice in applying the finish but avoid extreme heat.
- Consider thinned tung oil. Thinned tung oil has a lower chance of becoming gummy over the years compared to pure ones. Also, thinned oils dry faster, though it’s not food-safe due to the added solvents. Also, you have to aerate it well to allow the VOCs to dissipate safely.
- Give it time to cure. You can’t be impatient when using tung oil. This finish takes a long time to dry and harden fully, so you should dedicate at least two weeks to the curing process.
Can you sand gummy tung oil?
Sanding alone won’t remove gummy tung oil. It will likely scrape a small amount of the finish and damage the wood at the same time. It’s still best to use thinner to soften the oil first. Once it’s soft, you can scrub the wood gently using fine steel wool or high-grit sandpaper.
Remember that you only need to lift the hardened tung oil and not sand vigorously. This is crucial, especially if you’re working on old and expensive furniture.
How long does tung oil finish last?
Tung oil finishes can last for decades, but for optimal protection, woodworkers will re-apply a thin coat every six months. This is mostly done on wood installed outdoors where it’s exposed to higher levels of wear and tear.
Overall, the lifespan of tung oil finishes depends on the oil quality, the manner of application, and the area where it’s installed.
How should the tung oil finish look like?
A tung oil finish has a dark look with transparent and wet finish. If applied to dark-colored wood, it would also produce a deeper finish.
If you want to make wood darker, you can apply multiple coatings of tung oil. However, you should keep in mind that too many coats will make the hardened tung oil almost plastic-like.
Do you need to thin tung oil?
If you want to avoid a gummy finish in the future, thinning your tung oil is a good decision. It will also help in creating even stains as well as preventing the coat from being sticky.
If you are to dilute tung oil, you should use 7 parts solvent and 3 parts tung oil on the first coat. After that, the solvent should consist of 50%, 40%, and 25% for the next three coats, respectively.
However, you should also know that thinning tung oil will defeat its food-safe characteristic. For example, pure tung oil is applied to picnic tables since it has little to no off-gassing. But if mixed with solvents, tung oil would emit more toxic gasses.
Removing gummy tung oil finish is a simple process. You have to test it out first to ensure that the wood won’t sustain damages. Always choose a hidden spot on the workpiece, so the damage will be hidden if the process didn’t succeed.