While water and oil do not mix, you can use water-based polyurethane over oil-based stain. The reason why is the oil-based stain will be completely dry before applying the polyurethane. Find out the answer to all of your questions about the process and how to use water-based polyurethane over oil-based stain right here and get an amazing finish on your wood project.
Quick Answer
The short answer to whether you can apply water-based polyurethane over oil-based stain is yes, as long as the stain is completely dry. Keep in mind that water-based polyurethane can react to the oil-based stain. There are a few other factors to consider, which we will do below at great length to help ensure you get the finish you want on your project.
As long as the stain is entirely dry, water-based polyurethane can be placed over it. However, applying the polyurethane on the stain too soon can cause the polyurethane to rub off or damage the stain underneath. Therefore, the finish will need to be sanded off and the procedure redone to repair this.
Difference Between Water-Based and Oil-Based Polyurethane?
Oil-based polyurethane is exceptionally durable and adaptable and can be used for both indoor and outdoor projects. It does, however, have a strong and poisonous odor that is not good for the environment. Also, when dry, oil-based polyurethane has a light yellow tinge instead of a clear finish. Finally, oil-based takes longer to dry, a full day or even two and a month to cure.
Water-based polyurethane is less durable and does not perform well outside. It is, however, more environmentally friendly, as it contains no hazardous VOCs or odors. Even though it dries quickly, it takes a month to cure, but you can add extra coats much sooner. It can take as little as six hours to dry.
Before sanding, make sure the object is absolutely dry and not tacky, regardless of whatever option you choose. If you’re not sure, wait a little longer. Whatever you do, the project will take a month to thoroughly cure, even if it feels finished after two weeks. When it comes to floors, you can begin using them after two weeks, but try to avoid wearing shoes if at all possible.
Change of Color
The most important step to applying water-based poly over oil-based stain is to make sure the stain is completely dry before applying polyurethane. It’s best to let the stain dry for at least four days to allow all the minerals to evaporate off the surface of the item. This timeframe can change depending on environmental factors that can affect drying time, such as weather, humidity, ventilation, and more.
Patience is key as applying the poly too soon can cause problems later. Keep in mind that raising the grain of the wood before staining it is also a good idea because the water-based polyurethane will elevate the grain whether you want it to or not. The purpose of raising the grain is to open up the wood so it can soak in the stain better.
Dry stain is less susceptible to color changes from polyurethane. To avoid this, simply wait until the oil-based stain has completely dried before applying a thin coat of polyurethane. While it is still wet, it will change color. However, once the polyurethane has dried in most circumstances, this alteration should be reversed. Once dried, the water-based polyurethane should dry clear without altering the color of the stain.
Additionally, you can use mineral spirits or paint thinner in very small quantities before application of the water-based polyurethane. Go with the wood grain to remove tacky spots, and this step will help to ensure the polyurethane adheres well to the oil-based stain and helps to reduce the amber tone or yellowish tint later.
Steps to Applying Water-Based Polyurethane Over Oil-Based Stain
Here are the supplies and steps needed to properly apply water-based polyurethane over oil-based stain.
Supplies
- A project stained with oil-based stain
- Water-based polyurethane
- An applicator such as a synthetic bristle brush, roller, foam pad, or other
- Lint-free cloths
- Vacuum
- Mineral spirits or paint thinner
Step 1
Before applying the polyurethane, it’s imperative you make sure the stain is completely dry. Use the mineral spirits and lint-free, and if the stain comes off on the cloth, then it needs more drying time. Wait another day before checking again. (Note: if you wish to raise the grain, make sure to do so before sanding or staining. At this point, you are too late unless you would like to start from scratch and make extra work for yourself).
Step 2
Once the stain is completely dry, use the applicator of your choice (we recommend checking the manufacturer’s recommendations for applicators) to apply a thin, even layer of polyurethane to the project. Ensure you follow the grain of the wood and use the minimum number of strokes. Don’t worry, you will apply multiple coats to even out the layers. Leave the item to dry completely before applying the next coat. You may notice a few bubbles, but these will go away with a little help in the next step.
Step 3
Once the first layer of polyurethane dries completely, use 220 grit or finer sandpaper to remove bubbles and even out the finish. During this step, make sure to check for any blemishes too. Use the fingernail test to see if the poly has dried completely. If your fingernail leaves an imprint, then wait longer, but if it does not leave an imprint, then it’s ready.
Step 4
Now you will need to clean the surface again before moving on to the second coat. Start by removing all the dust with a vacuum or clean lint-free cloth. Any dust or debris left on the surface can ruin the polyurethane and final finish. After, use a wet cloth to go over the surface and then allow it to dry completely before moving to the next step.
Step 5
Now you are ready for the second coat. Keep the coat thin but a little thicker than the last coat to avoid bubbles. Again, allow the coat to dry completely before moving on to the next step.
Step 6
Repeat the steps above for the third coat remembering to sand between coats for the right finish. Most people are happy with two coats; however, some want a more durable finish. Do not miss any of the steps to avoid any complications.
Step 7
If you want a beautiful and professional finish, then finish with some steel wool and wax. While neither is necessary, they will help to improve the appearance and durability of the item.
Drying Time
Oil-based products take longer to dry, but the stain can usually dry in a couple of hours, unlike oil-based polyurethane. However, the water-based polyurethane will take about eight to 24 hours to dry, depending on the temperature. For colder or more humid weather, you may want to allow a full 72 hours for the products to dry and cure.
Amount of Coats Necessary
Water-based polyurethane is not as durable as the oil-based option, which is why we recommend a minimum of three coats but no more than five for a smooth and even finish. For raised wood, though, you may need up to eight coats for a smooth finish.
Because you must thin it out with mineral spirits and prime the surface before applying subsequent coats, the first coat takes less time to dry. You must wait approximately 24 hours before sanding and applying the next layer. The subsequent coatings will take one to two days to dry before you can sand them. If you apply three coats, the process will take at least a week to dry and a month to cure.
Sanding
Make sure to sand before applying the stain, but you do not need to sand the stain again. However, you will need to sand between layers of the polyurethane to reduce bubbles and improve the smoothness of the finish. Thankfully, wood absorbs stains nicely and allows polyurethane to adhere with ease.
Toxicity
Both stain and polyurethane emit VOCs or volatile organic compounds, which are toxic. Keep in mind those that using both will not make the products more toxic, especially since you will not be using them while both are wet. Once the stain dries, it no longer sends out VOCs into the air, and polyurethanes work the same way. Additionally, water-based polys are even less toxic than their oil-based counterparts.
Pros and Cons of Using Water-Based Poly over Oil-Based Stain
Water-based polyurethane has no notable advantages or disadvantages over oil-based polyurethane. However, there is one consideration that you must keep in mind before proceeding. Water-based polyurethanes aren’t recommended for use over lacquer or shellac.
The cost of employing water-based polyurethane instead of oil-based polyurethane is another disadvantage. Water-based poly is twice as expensive per square foot as oil-based poly.
FAQ’s
How long does stain take to dry?
Oil-based stain can trick you into thinking it’s dry before it is, and you should always test for full dryness. First, run a mineral spirit-soaked cloth over the stained wood to see if the stain is dry. If any color appears on the material, the stain is not yet dried, and you should wait at least one more day. Repeat the test after a day. If no color appears on the material, repeat the test in a few more spots to be sure. After then, the stain is considered dried.
What’s the difference between water-based and oil-based stains?
Water-based stains take a bit longer and more effort to apply than oil-based stains, but they last much longer. Oil-based stains are easier to use and require less effort, but they do not persist as long as water-based stains. They’ll also have more mold, mildew, and algae issues in the future, as well as more maintenance. Before you begin your deck staining project, figure out which type of stain will work best for you.
How many coats of polyurethane do I need over stain?
One to two coats should be applied over stain for the most durability and longevity. Three coats offer the best protection and can help to make the finish a bit smoother too. After applying the polyurethane, also make sure to use steel wool to get a consistent sheen and then a paste wax for a fabulous luster. While not necessary, these last two steps can make a piece look professional.
Is water-based poly better than oil-based?
Both are equally good but with different pluses and minuses. If you want less smell and quicker drying time, then water-based is the better option. However, if you want a more durable finish ready to handle high traffic, then oil-based makes a better choice.
How can I avoid brush marks?
Avoid brush marks by using a roller instead of a brush to apply polyurethane. A roller also produces a more even finish, making it a good choice for larger projects. Use a paintbrush for covers and small spots and sand to remove the brush marks with fine-grit sandpaper with even pressure. Clean after and follow these steps after each layer.
Conclusion
Now you know that water-based polyurethane can be applied over oil-based polyurethane, and we know that it’s fine to do so as long as the application’s surface is clean and free of debris and grease. Next, removing any traces of grease from the oil-based finish is necessary using the processes outlined earlier in this article. Lastly, it’s important to ensure the surface is dry and cured after the stain to ensure proper adherence of the polyurethane over the stain.