Can You put Water-based Polyurethane over Oil-Based Polyurethane?

Learn if you can put water-based polyurethane over an oil-based polyurethane

When I first started learning about polyurethane, I had to practice on my old furniture. Just like you, I eventually had to ask if it was okay to apply water-based polyurethane on what was previously finished with oil-based polyurethane.b

What I discovered has come in handy over the years, and I’m so glad I found out early.

Before I answer the question – “can you put water based polyurethena over oil based polyurethane“, let me give you a heads up on what you’ll learn from this article:

  • If and how to put water-based polyurethane over oil-based polyurethane
  • When it is okay to apply different types of polyurethane
  • Benefits of using water-based polyurethane

Time to kill the suspense.

Can you Put Water-Based Polyurethane Over Oil-Based Polyurethane?

Yes, you can apply water-based polyurethane over oil-based polyurethane. Given that both bases accomplish the same task, using one on top of the other is not a problem, whether for a refinishing job or a new project.

Some woodworkers like to start off with an oil-based finish to bring out the beauty of the wood, then top it up with water-based polyurethane.

In order to do that effectively, there are some crucial steps to follow, and the first one works in all cases.

How to Apply Water-Based Polyurethane Over Oil-Based Polyurethane

Can You put Water-based Polyurethane over Oil-Based Polyurethane image
Photo credit: Santiago’s Hardwood Flooring

Given their different constitutions, you would think water-based, and oil-based finishes don’t go together, probably because oil and water don’t mix.

However, when it comes to woodworking, you will find that there are very few things you can’t put together, provided you follow the proper protocol.

Materials you’ll Need:

  • 220 grit sanding paper
  • 320 grit sanding paper
  • Vacuum cleaner
  • Tack cloth
  • Synthetic nylon bristle brush
  • Water-based polyurethane

Step 1: Wait for the Surface to Dry

This is the most important step in all polyurethane applications, whether water-based on oil-based or oil-based on water-based. Always wait for the wood to dry!

For old furniture, this step is already taken care of, so jump to step 2.

If you have just applied the oil-based polyurethane, wait at least two weeks for it to cure. Just like we mentioned, oil and water don’t mix – when wet.

While two weeks is usually sufficient, you can play it safe and wait for two months. Dry times depend on temperature, humidity, and the type of finish. Ensure that the oil-based polyurethane is no longer tacky before you move on to step 2.

Note that you only need to wait this long for the first application.

Step 2: Sand the Existing Coat

For this, you will need either 220 grit paper or 320 grit paper. 220 grit sandpaper is more coarse than 320 grit, so I recommend this for older furniture. A refinishing job will require a bit more work as the condition of the wood may not be ideal.

It may have a few dents and bruises, so you need a bit more elbow grease, or grit power, to smooth the surface.

If what you are doing is your own water on oil job, then 320 grit should suffice. You can also use 220 grit paper for this, but remember that you are sanding lightly, not aggressively, just enough to improve adhesion.

Step 3: Clean the Wood

Dust is the enemy of a good sanding job. Therefore, you have to ensure that all of the dust from the sanding is not just cleaned but disposed of far away from your work site.

Start with a vacuum cleaner and gently hover over every inch of the surface. Follow that up with a tack cloth.

Tack cloths do a better job of cleaning than vacuums, so you may choose to go without the former on smaller tasks. However, if you are working on floors and other large surfaces, you should definitely use the vacuum first.

Step 4: Prepare the Polyurethane

As with standard applications, stir the water-based polyurethane before using it. Shaking it will add bubbles to it, and you really don’t want that mess.

Use a wooden stick to give it a gentle stir, then jump right into the next step.

As part of your preparation, you may choose to thin the water-based polyurethane with water, but you don’t have to. In fact, most manufacturers recommend that you shouldn’t thin any type of polyurethane.

Step 5: Apply the First Coat of Water-Based Polyurethane

Now, you are ready to do what you came here for. With your synthetic nylon bristle brush or any other brush recommended by the manufacturer, apply the water-based polyurethane along the grain.

A common myth is that applying across the grain then along the grain will enable the wood to absorb the polyurethane better. All that does is leave you with a huge mess you’ll need to sand down.

Applying the finish with the grain brings out the natural beauty of the wood and is less likely to leave brush marks or cause bubbles.

Step 6: Sand Again

After the wood has dried for about two hours, you should sand it again. This time, use 320 grit paper for the same reason as before. Again, you only want to make slight abrasions so that the next coat will adhere better.

Another reason for sanding is to get rid of imperfections like polyurethane bubbles and dust nibs. Most of the bubbles should disappear within five minutes of application. But if they don’t, the sandpaper will get rid of them swiftly.

Step 7: Apply Another Coat

Are 2 coats of polyurethane enough? Well, for routine jobs, you would need to apply three coats of water-based polyurethane. However, this isn’t a regular job, so you may need to apply several more coats.

You may not have to sand between subsequent coats, provided there are no bubbles or dust nibs. However, you should wait at least two hours between each coat before reapplication. That way, you not only wait for the coat to dry, but you can ensure there are no blemishes.

What are the Benefits of Applying Water-Based Polyurethane Over Oil-Based Polyurethane?

Photo credit: Wigglywisdom

The main benefit of putting water-based polyurethane over oil-based polyurethane is noticeable in the long run. Over time, oil-based polyurethane has an amber hue.

Water-based polyurethane, on the other hand, dries clear and remains clear. 

Besides this, you might prefer to use water-based polyurethane for refinishing jobs because it is less toxic, dries quicker, and does not require as much sanding or thinning.

In terms of protection, they are equally as good. Some might argue that oil-based polyurethane is better, but those are probably old cats. New water-based polyurethanes last equally as long.

Just make sure you buy the right brand.

Water-Based Polyurethane Over Oil Based Polyurethane FAQs

Can You Use Water-Based Polyurethane Over Oil-Based Stain?

Yes, you can apply water-based polyurethane over oil-based stain. You may be thinking, “But oil and water don’t mix,” and you’ll be right. You won’t be mixing them; you’d just be applying the polyurethane over the stain. Learn how to apply water-based polyurethane over oil-based stain to avoid any blunders.

Can You Put Water-Based Polyurethane Over Oil-Based Paint?

Yes, you can put a water-based polyurethane over an oil-based paint finish in most cases. Prepare the surface first by removing any dirt, grease, and wax before using water-based polyurethane over oil paint.

Can You Put Oil-Based Polyurethane Over Water-Based Polyurethane?

Yes, you can use water-based polyurethane over oil-based once the water-based coating has fully cured. It would help if you buffed the water-based poly a little in preparing for coating with the new oil-based poly.

Which is Better Oil or Water Based Polyurethane?

Oil-based poly looks better than water-based. The oil-based polyurethane has more depth in terms of – color and shine. Even better, the final look is just expected when used on hardwoods as opposed to the duller colour of water-based polyurethane.

Ready to Apply Water-based Poly Over Oil-based?

It was such a huge relief to find out I can put water-based polyurethane over water-based polyurethane. This gives woodworkers the freedom to take on old and new projects with confidence.

If you start working with oil-based poly and don’t like the way it looks, you can easily change to water-based and vice versa.

Now that you have this information, are you ready to take it for a test run? Let us know what you will be working on next and where you stand on the debate: oil-based polyurethane vs. water-based polyurethane.

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