How to Use Oil‐Based Polyurethane over Water‐Based Polyurethane

Co-authored by Sam Hubbard

Last Updated: July 7, 2023

Oil and water are famous for repelling one another and not mixing. Luckily, you can still apply an oil-based polyurethane over a water-based one. If you already laid down a water-based finish and decided to go for an oil-based one, do not fret. With a little bit of extra time and preparation, you can apply the oil-based finish right over the water-based one.

Part 1

Part 1 of 4:

Prepping the Floor

Download Article

1
Make sure that the water-based polyurethane coating is fully cured. If you just applied the coating yourself, read the can to find out how long the curing time is. Some brands take longer than others, but it is typically between 30 to 60 days.^{[1]
X
Research source}
- If you don't know whether or not it's fully cured, consider waiting 30 to 60 days.
- If the surface is cool to the touch, it's not dry. If you sand it lightly and get a fine powder, it is dry and ready to go.^{[2]
  X
  Research source}
Choose something that is around 150-grit. You can do this with sandpaper or with a power buffer. Use a light touch while buffing so that you don't accidentally cut through the water-based finish.^{[3]
X
Research source}

Advertisement
Wipe smaller surfaces clean with a dry cloth and vacuum larger ones. Lastly, vacuum the floor to get rid of any traces of dust.
A damp that's been dampened with mineral spirits will work the best.^{[4]
X
Research source} Alternatively, you can use a tack cloth of a dust cloth. This will get rid of any dust, which may mar your final finish.

Part 2

Part 2 of 4:

Setting Up Your Work Area

Download Article

This is very important. Not only will you be working with lots of sanding and dust, but you will also be working with chemicals. If it is not possible to take your project outside or into an open garage, open up a window.
Make sure that it is rated for organic fumes. This will help further protect your lungs against the harmful dust and fumes.^{[5]
X
Research source}
This means vacuuming the room and wiping down your work surface. If you have something in the room that might give off dust, such as a hanging rug or tapestry, it would be a good idea to remove it temporarily. You don't want to see any dust particles floating in the room.
Using it at half strength will make it act more like a wiping varnish. It dries faster and is easier to sand. If you want to use it at half strength, you'll need to dilute it with paint thinner.
5
Dilute the polyurethane, if needed. Purchase two cans of oil-based polyurethane. Set one of the cans aside to use for later layers. Dilute the remaining can with equal amounts of paint thinner.
- Not all paint thinners are suitable for oil-based polyurethane finishes. Make sure that you use the right kind.

Part 3

Part 3 of 4:

Appling the Oil-Based Coating

Download Article

1
Apply the polyurethane using a wide brush. Choose a bristle or foam brush that is about 2 inches (5.08 centimeters) wide. Make sure that you brush with the wood grain rather than against it. If you get any bubbles, brush back over them lightly; this will help them pop.^{[6]
X
Research source}
- If you diluted one of your cans of polyurethane, then you should apply the diluted one now.
How long this takes depends on the brand you are using. Most oil-based polyurethane finishes will cure overnight if it is warm enough. Some may take much longer, so read the instructions on the label carefully.^{[7]
X
Research source}
Use sandpaper or a power buffer that is at least 280-grit; 320-grit would be better, however. Once again, use a light touch so that you do not sand through it.^{[8]
X
Research source}
A tack cloth is a special, sticky cloth for this exact purpose. You can buy one at a paint supply store. If you can't find a tack cloth, you can vacuum the dust up instead. It would still be a good idea to wipe the surface down with a damp cloth, however.^{[9]
X
Research source}
Let each coat cure first, then sand it smooth. Wipe the coat clean with a tack cloth, then apply the next one.^{[10]
X
Research source}
6
Allow the final coat to cure completely. Once the coat cures, you can use the wooden piece. If you coated a floor, then you can move back all of your rugs and furniture. If you want a high-gloss finish on your piece, then continue on to the next section to learn how to obtain it.
- After the final coat, use a piece of cardboard to buff the surface and make it especially smooth.
- A high-gloss finish is not necessary or recommended for floors.

Part 4

Part 4 of 4:

Polishing the Surface (Optional)

Download Article

Start with a 320-grit, then move onto a 400-grit, and finally 600-grit. Use the same method as before, then wipe the surface clean with a cloth dipped in mineral spirits.^{[11]
X
Research source}
Shake the can for the amount of time recommended on the label. Hold it 12 to 16 inches (30.48 to 40.64 centimeters) away from the surface, and spray on a light coat using a sweeping motion.^{[12]
X
Research source}
This should only take a couple of hours, but it may take up to a day or two. If the coating feels tacky to the touch, it is not cured.
Shine a bright light on the surface, and take a look at it from an angle. If you see any specks of dust, you'll need to gently buff them out with 1,500-grit sandpaper. If you don't have any on hand, you can use a brown paper bag instead.^{[13]
X
Research source}
Gently go over the entire piece using small, circular motions. Keep polishing until you get the level of shine you desire.

Expert Q&A

Search

Add New Question

Ask a Question

200 characters left

Include your email address to get a message when this question is answered.

Submit

Tips

If the polyurethane is too thick, thin it by 10% with mineral spirits.^{[14]
X
Research source}

Thanks
Helpful 0 Not Helpful 0
Work in an area with lots of reflected light. This will help you spot any bubbles or unevenness.^{[15]
X
Research source}

Thanks
Helpful 0 Not Helpful 0
Use a clean brush for each coat. If the finish dried on the brush, you'll need to get a new one.^{[16]
X
Research source}

Thanks
Helpful 0 Not Helpful 0