Can You Put Water Based Polyurethane Over Oil Based Polyurethane?

Layering finishes can be tricky. You might be staring at that oil-based polyurethane and wondering if a water-based topcoat is the right move.

Compatibility between these two types of finishes is a common concern. Mixing oil and water doesn’t usually end well, but in the world of wood finishes, the rules are different.

This blog unpacks the do’s and don’ts of combining these two finishes. If you’re looking for clarity and a smooth, durable result, let’s break it down step by step.

Can You Put Water Based Polyurethane Over Oil Based Polyurethane?

Yes, you can apply water-based polyurethane over oil-based polyurethane, but proper preparation is crucial.

Ensure the oil-based layer is fully cured, lightly sand the surface to remove gloss, and clean it thoroughly.

This ensures proper adhesion and a smooth finish. Always follow manufacturer instructions for best results.

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

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.

Required materials:

Below are the required materials you will need to apply water-based poly on oil-based poly.

• 220 grit sanding paper
• 320 grit sanding paper
• Vacuum cleaner
• Tack cloth
• Power buffer
• Synthetic nylon bristle brush
• Mineral spirits
• Water-based poly

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 drying times.

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

If you have just applied the oil-based poly, wait at least two weeks of curing time. 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. Curing time depends on temperature, humidity, and the type of wood finish.

Ensure that the oil-based finish 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 surface 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 to use a light touch, not aggressively, just enough to improve adhesion.

Step 3: Clean the surface

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 surface and site.

Start with a vacuum cleaner and gently hover over every inch of the surface. Follow that up with a tack rag dumped in mineral spirits.

Tack cloth or damp cloth 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 to make your surface dust-free.

Step 4: Prepare the polyurethane

As with standard applications, stir the waterbased poly 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 new water-based finish 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 surface grain.

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

Applying water-based polyurethane along 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 surface 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 all the 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 poly. 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 be fully cured, but you can ensure there are no blemishes.

Related read: Can I put polyurethane over Danish oil?

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

The main benefit when you apply water-based polyurethane over oil-based poly is noticeable in the long run. Over time, oil-based polyurethane has an amber hue color.

Water-based poly, on the other hand, dries clear, remains clear, and forms a harder coating.

Besides this, you might prefer to use water-based finish 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.

Related post: Can I use poly over chalk paint?

Can You Put Oil Based Polyurethane Over Water Based Polyurethane?

Yes, you can apply oil-based polyurethane over water-based polyurethane. However, the surface must be fully cured and lightly sanded to remove any gloss.

This helps the oil-based layer adhere properly. Ensure the surface is clean and dust-free before applying the oil-based polyurethane for a smooth and durable finish.

Can I Put Water Based Poly Over Oil Based Poly: FAQs

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

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.