Can you apply water based polyurethane over oil based? Well, oil based polyurethane contains solvents that emit into the environment as toxic fumes.
So how do you limit the toxicity of oil polyurethane without removing it entirely from the surface? Is the application of water based polyurethane over oil based viable?
Yes, you can put a water-based polyurethane over an oil-based one.
The most important step is proper preparation; clean the surface to remove dirt, wax, and grease.
Then, lightly sand over the oil based polyurethane before applying the water based polyurethane in light coats.
Though made of different solvents, water-based and oil-based polyurethane achieve the same task, giving your wood surface the perfect finish.
Therefore, using water on top of oil or water-based polyurethane is not a problem. You only have to learn the know-how to apply them.
Table of Contents
What Is Polyurethane?
Polyurethane is a protective coating that creates a solid plastic layer when applied on a wooden surface.
The clear finish is applied on wooden surfaces such as flooring, kitchen cabinets, furniture any wood projects you can think of.
The finish from polyurethane often comprises resins, making the product more robust than regular varnishes or lacquers.
Polyurethane is a great option, leaving your wooden surface stronger for longer.
Unlike other finishing products on your woodwork, polyurethane is more flexible as it can work on all-shaped surfaces.
The coating from polyurethane gives your wood surface an admirable resistance from abrasion, scratches, and spills.
Besides, it has also proven resistant to boiling water and harsh chemicals like acids.
If you are searching for a hard-wearing clear finish for your wood surfaces, look no more!
I’ll address most of the things you need to know about polyurethane.
What Is Water-Based Polyurethane?
Water-based polyurethane is a polyurethane finish that uses water instead of solvents as a base for carrying polyurethane solids.
Water-based polyurethane, just like the oil one, will give your wood a hard protective film if applied in several layers.
It dries faster than the oil-based polyurethane, thus allowing you to add as many coats as possible till you achieve your desired look.
Water-based polyurethane is your to-go if you are a woodworker sensitive to smell. It has no odor.
Cleaning a surface coated with water-based polyurethane is quite fast, as you only need soap and warm water.
What Is Oil-Based Polyurethane?
Unlike water-based polyurethane, which uses water, oil-based polyurethane uses petroleum and mineral solvents to form the base of the polyurethane solid.
Oil-based polyurethane solids come in a wide variety. You can always get it at your local store as it is still widely used and sold.
Depending on your preference and how you want to work, you can find an oil-based polyurethane in brush or spray format.
The product creates a hard and protective shell.
Unlike a water-based polyurethane which needs several layers, you will need fewer oil-based coatings to achieve your desired outcome.
Oil-based polyurethane is best when you have plenty of time to work on your finishing.
It dies slowly, as a single coat may consume up to two hours before it dries off.
Adding more layers will demand about six hours of your time, depending on your room temperature.
Although the oil-based polyurethane may have some odor, it will fade away as soon as the product cures.
Cleaning an oil-based polyurethane wooden surface requires a paint thinner or some mineral spirits.
How to Apply Water-Based Polyurethane Over Oil-Based Polyurethane
You are probably wondering how to apply water-based polyurethane over water-based, yet the two components don’t mix.
The art of woodworking allows you to mix almost everything. You only need to follow the proper procedures.
You will need the following materials to apply water-based poly on an oil-based poly:
- 220 & 320 grit sanding papers
- Vacuum cleaner
- Tack cloth
- Power buffer
- Synthetic nylon bristle brush
- Mineral spirits
- Water-base poly.
Once you have assembled all the materials, follow the procedures below.
Step 1: Allow Your Wooden Surface to Dry
Simple as it seems, this is the most crucial step in your polyurethane application.
If you are renovating old furniture, this first step is unnecessary.
However, if your surface has a new oil-based poly, wait for about two weeks of curing time.
The process will fail if your surface does not cure as required because water and oil don’t mix.
While two weeks is enough for your oil-poly surface to cure, we encourage you to wait for up to 2 months just to be safe.
The curing period differs depending on your room temperature, humidity, and the type of finish.
Once your finish is no longer tack, proceed to the next step.
Step 2: Sand the Existing Coat
You will need 220 or 320-grit sandpaper for this step.
The 220-grit sandpaper is coarser than the 320, hence recommended if you are working on an old piece of furniture.
The sanding may leave your surface with a few dents. Therefore, you will need more elbow grease or grit powder to smoothen your surface.
Step 3: Surface Cleaning
Dust often ruins a good sanding job. You must be keen to remove all the dust from the sanding exercise.
Clean and dispose of the dust away from your working area.
Using a vacuum cleaner, hover over every corner of the surface to eliminate any unwanted material.
After vacuuming, use a tack rag dumped in mineral spirits.
Note that a tack or a dump cloth cleans better than vacuums. You, therefore, may want to use it instead.
If your working surface is as big as a floor, use a vacuum first to ensure there is no bit of sand left.
Step 4: Polyurethane Preparation
Gently stir your water-based polyurethane before using it, avoiding shaking it as it will create bubbles, leaving you with an undesirable mess.
Stir using a wooden stick.
While most manufacturers discourage would workers from thinning their polyurethane, there is no harm if you thin your new water-based finish using water.
Step 5: Apply the First Layer of the Water Based Polyurethane
Use your synthetic nylon bristle brush to apply the water-based poly along the surface grain. You can also use any other recommended brush.
There is a common misconception that applying your water-based polyurethane across instead of along your grain will allow for better absorption of the poly.
However, this is a wrong belief as it will only leave your surface messy and with more work for you to sand down.
Applying water-based poly along the grain makes your wood look naturally beautiful.
It also reduces the chances of water brush marks appearing on your finish or, worst, causing bubbles.
Step 6: Redo the Sanding
Allow your surface to dry for about two hours, then sand it again.
In this step, ensure you use the 320-grit paper because you only want to make slight abrasions.
By doing that, you are leaving room for your next coat to adhere much better.
Sanding also clears any imperfections, such as polyurethane bubbles and dust nibs.
Under normal circumstances, the bubbles will disappear within five minutes of application.
If they don’t, don’t panic! Your sandpaper will get rid of them in a blink.
Step 7: Add Another Coat
If you are doing a routine job, you may only need three coats of water-based poly.
However, since this is not a regular job, I recommend applying several more coats.
Sanding may be unnecessary in the subsequent coats as long as your finish has no bubbles or dust nibs.
You must wait about two hours between each coat before adding another layer.
Waiting for two hours allows your coat to fully cure while giving you a clear view of your finish.
Ensure that there are no blemishes.
Here’s How to Apply Water Based Polyurethane:
Benefits of Applying Water-Based Polyurethane Over Oil-Based Polyurethane.
Applying water-based over an oil-based poly is beneficial in several ways. One of the main benefits is the color of your finished wood surface.
While an oil-based polyurethane has an amber hue, the water-based poly is likely to retain your wood’s natural color.
It not only dries and remains clear but also forms a harder coating.
Water-based polyurethane is also recommended because it is less toxic; it does not produce smells that are likely to choke you as you work on your wood.
Woodworkers highly sensitive to smell would choose water-based poly for this quality.
Besides, water-based polyurethane is best, especially when working on a fixed schedule.
It dries quicker than an oil-based poly. Working with it is also easily manageable as it does not require much sanding or thinning.
Water-based polyurethane will also offer your wood surface solid protection.
The brands currently produced are of excellent quality. They will probably last you as long as the oil-based polyurethane will.
Be sure to get the right brand for the best results.
Frequently Asked Questions
Some of the most asked questions about this topic include:
Can You Use Water-Based Polyurethane Over Oil-Based Stain?
Yes, applying water-based polyurethane over an oil-based stain is possible.
You probably are wondering again, how? Yet oil is not soluble in water?
The similar way oil and water don’t mix is the same way you will not be mixing your water-based poly over an oil-based stain.
You will achieve a smooth finish using the proper procedures when applying the water-based polyurethane over the oil-based stain.
Can You Put Water-Based Polyurethane Over Oil-Based Paint?
Yes, you can apply your water-based polyurethane over an oil-based paint wood.
Get the best results by prepping the surface first. Remove any dirt, grease, and wax using a vacuum cleaner or a damp cloth.
Once clean, apply your water-based poly over your oil-based paint. Applying water0based poly over oil-based poly is such a game changer!
It gives a woodworker the freedom to confidently take up old and new projects. It also allows you to make mistakes and rectify them whenever possible.
If you start working with an oil-based poly and feel dissatisfied, don’t worry! You can easily change it to a water-based poly or vice versa.
Be keen to follow the proper procedures for a perfect finish.
Can You Put Oil-Based Polyurethane Over Water-Based Polyurethane?
You can apply your oil-based polyurethane upon drying and curing your water-based coat.
Consider polishing your water-based polyurethane surface for desirable results before covering it with the new oil-based poly.
Oil Based or Water Based Polyurethane, Which Is Better?
While both types of polyurethane can give you the perfect finish you are looking for, the oil-based poly outshines the water-based.
The final appearance of the oil-based poly is way better than that of the water-based. It will offer you more depth in color and shine.
Also, if you are working with hardwoods, you want to consider the oil-based ones, as they will give you the amber color you desire.
Water-based poly is much duller; it has no shine as it most likely will retain your wood’s natural color.
However, no one size fits all. You will decide which polyurethane is better based on your needs.
The water-based is best for you if you want your wooden surface all-natural looking.
If you want to enhance your surface’s appearance and make it glossier, oil-based polyurethane should be your perfect pick.
What Is the Drying Time of Polyurethane?
In deciding the type of polyurethane, you would use as a finishing to your wood surface, you can use one of the water-based or an oil-based poly.
Depending on your needs, both of them will give you excellent results.
When using water-based polyurethane, the question of how long you should wait for it to dry up always arises.
The time length varies depending on the type of surface you are working on.
Other factors are your coat’s thickness and the working environment’s humidity and temperature.
Generally, a water-based polyurethane will take at least two hours to dry between the coats.
Also, note that you should only apply up to two coats of water-based poly daily.
After six hours, your water-based polyurethane should be dry enough that you can walk on with socks. Keep your pets off the floor.
Within 48 hours, your water-based poly will be completely dry. Also, be sure to leave it uncovered for two weeks.
After 30 days, your water-based poly will have cured.
Since temperatures are a crucial determining factor over how long a water-based poly takes to dry, the recommended temperatures should be between 60 and 90 Fahrenheit.
If applied on a floor surface, your water-based polyurethane will take up to 24 hours after the last coat to dry up.
It takes 24-48 hours for an oil-based polyurethane to dry up.
After an estimated 24-hour period, you can comfortably walk on your oil-based polyurethane floor finish.
The floor should appear dry and not have a tack feeling on your touch.
Keep your pets off the floor before it the coat cures. Remember to wear your socks as you walk around.
After a minimum of 24 hours, you can start sanding based on your project or add another layer.
Forty-eight hours post your last polyurethane coat is enough for it to dry up comfortably.
You can now walk with your shoes on without feeling tacky. Within four days, your oil-based poly will be completely dry.
However, wait until two weeks before you allow your pets around. After a whole month, your oil-based poly will have cured completely.
Drying Vs Curing
Now that we have discussed how long it will take before your polyurethane dries, keep in mind the difference between drying and curing.
Consider your polyurethane dry when your surface does not feel tack and does not have a wet appearance.
If dry, you can comfortably walk on the floor. Be keen not to walk roughly as it can give your wooden surface wrinkles and blemishes.
Also, avoid moving furniture around or setting down anything heavy until your polyurethane completely cures.
Your polyurethane varnish will be entirely cured by the chemical reaction between the polymer molecules and oxygen.
The reaction allows the molecules to bind firmly, thus minimizing any chances of damage or wrinkling on your floor.
Unlike drying, which takes hours, curing takes an average of 30 days. Therefore, you should be extra careful around the floor for about a month.
Polyurethane Varnish Sheen
The question “how long does polyurethane take to dry?’ goes hand in hand with “what kind of sheen in my polyurethane dries faster?”.
Different sheens have different properties, which you must consider before applying on your hardwood floors.
- High Gloss polyurethane. The high gloss will give your floor a desirable heavy-duty, and shiny.
However, the components in their shining appearance increase the time it takes to dry up.
- Semi-gloss. You will likely find a semi-gloss polyurethane in most of your wooden surfaces: the cabinets, floors, doors, and a lot more in your woodworking projects.
While this varnish will give you a glossy surface, you will not achieve the kind of “shine” with a high-gloss polyurethane.
- Satin. Of all the varnish sheens available, satin offers the fastest drying process. Its shine is not as much as a high-gloss poly. It is subtle and very durable on your matte surface.
Side note: you may want to use the satin sheen to shorten drying time. If you are not a fan of a gleaming appearance, then the satin sheen is what you need.
- Matte. Your manufacturer will label this varnish as either matte or flat. Such a varnish will leave no shine or gloss on your wooden surface. Its drying period is a bit shorter than that of high-gloss and semi-gloss.
Factors Affecting the Drying Time of Polyurethane
Several factors determine the dry and cure time for any polyurethane. As earlier noted, water-based polyurethane dries up faster than oil-based.
However, there are still other crucial factors to consider. Depending on your brand, some polyurethane manufacturers often include drying agents in their products.
These agents fasten up the drying period, especially for an oil-based polyurethane.
Other manufacturers include natural oils, different solvents, or stains for coloring in their polyurethane brands.
All these features influence the drying period of a polyurethane. Other factors that affect the drying time include the following:
Cleaning is a vital step in the application of polyurethane. The dirt elements will likely stick under your varnish if the floor is not perfectly cleaned.
Such a misstep will reduce the quality of your wood surface and increase the drying time.
To avoid such an unwanted outcome, ensure that your working surface is thoroughly clean before applying the varnish.
Type of Wood Surface
There are wood varieties that all have different drying abilities.
If you are working with raw and sanded wood, your first polyurethane court will quickly dry up and absorb.
However, every coat added to another will take longer to dry up.
For instance, polyurethane applied on a live edge wood would take less time to dry than a traditional piece of lumbar.
The temperatures during hot weather will fasten the drying process of your polyurethane.
Unlike hot temperatures, cold weather increases the drying period by up to 24 hours. Also, leave your windows open, changing your room temperature.
I encourage opening the windows even in cold weather as it will give you proper ventilation.
Also, while working during the cold days, consider wearing protective gear if you are reluctant to open the windows.
Doing so will protect you from fumes that may otherwise intoxicate you.
An increase in humidity will equally increase your drying and curing time.
With increased humidity, moisture stays in the air for longer, thus slowing down the drying process of your finished surface.
Check the temperature and humidity on the day you intend to vanish.
Doing so will help you estimate the drying time of your polyurethane. If the humidity exceeds 50%, anticipate a more extended drying period.
Type of Wood
The wood species, like the wood surface, influences the drying time of your polyurethane.
Woods that contain more oil will take longer to dry.
For instance, aromatic cedar and rosewood will take longer to dry because their oil does not readily absorb polyurethane.
The Number of Coats Applied
The number of coats you apply to your finish will affect the drying time.
When you do more coats, it will take longer to dry up. Fewer coats translate to a faster drying period.
While applying, be keen to apply thin layers as they dry up quicker than thicker ones.
Applying extra coats during hot temperatures is a plus, as they will dry even more quickly.
Ventilation in your working room also affects the drying period. Some woodworkers choose minimal ventilation by closing the windows.
Doing so prevents dust or allergens into the room, which may stick under the varnish.
This will only work well when using water-based polyurethane, as it dries faster than an oil-based poly.
Oil-based polyurethanes have quite an odor, hence the need for proper ventilation.
However, leave the windows open if you want your wooden surface to dry up faster, regardless of the type of polyurethane you use.
The dust is unlikely to return to the room unless the weather is very windy. A fan is a plus for your ventilation too. It also fastens your drying time.
Generally, the average drying time of the oil-based and the water-based poly is between 24-48 hours.
However, different things determine how long your surface will take to dry up.
Expect longer or fewer drying hours depending on your environmental conditions, the type of wood, and the number of coats you are applying.
How to Make Polyurethane Dry Faster
Most woodworkers prefer an oil-based polyurethane over a water-based one because of its beautiful glossy finish on their wooden surfaces.
However, one primary con of using oil-based polyurethane is that it takes longer to dry and cure.
The following tips will help you speed up the drying period.
- Work with a high-build polyurethane. Different manufacturers offer different qualities for their brands.
High-build polyurethanes like Minwax are designed to offer you a durable finish with just two layers. We previously mentioned that the more coats, the slower the drying process.
While using this product will not speed up the drying time, it will reduce the number of coats you need on your surface.
The fewer the coats, the faster your wooden surface dries and cures.
Products like Rust-Oleum Varathane Triple Thick is a reliable and high-build polyurethane formula. It is water-based.
You only need to apply a single coat coverage to achieve your perfect finish. The coat will dry up within two hours of application.
- Work with a fast-drying polyurethane. Minwax products like the Minwax super-fast-drying polyurethane are oil-based and designed for hardwood floors.
It has an optimized drying technology that will offer you faster second coats. If this is your choice, be keen to apply a thin coat using a recommended brush or foam.
Allow it to dry for 4-6 hours, then sand it with high grit sandpaper.
- Ventilation. If you cannot access a high-built or fast-drying polyurethane, allow proper air circulation by opening your windows and doors.
Enhance this by using large floor fans to allow air to move around your project. This will speed up your drying time.
Since humidity also slows down the drying process, using a dehumidifier will work magic for you. Dehumidifiers are relatively affordable.
The collection buckets are designed to shut off once complete. Therefore, remember to empty it now and then.
- Heat. We discussed earlier that high temperatures speed up the drying process.
Even though increased temperatures will speed up the drying time, the curing period will remain the same.
Depending on the size of your project, you could use a hair dryer in your working area to increase the heat.
If your project is bigger, a heat lamp or a space heat will work best for you. Also, remember to use the hit alongside a dehumidifier for best results.
- Cleaning surfaces. Dirt trapped under your varnish will increase the drying time.
To avoid this, ensure that your wooden surface is as clean and smooth as possible. This will allow your polyurethane to dry faster.
While you may want your project completed as soon as possible, it is also essential to stay patient.
If you speed up the drying times too quickly, you will make a mess on your first coat.
If your product is taking longer to dry than recommended, seek help from your manufacturers before opting to “speed it up.”
Safety Tips When Using Polyurethane
- No smoking. Due to its highly volatile nature, ensure that there are no open flames, and no one is smoking around your working area.
- Fire safety. Fire may start for whatever reason, so don’t risk being caught off-guard.
As you may be working in a well-ventilated area, avoid fire risk by ensuring that you have a fire blanket and a fire extinguisher in your workshop.
- Face mask. A facemask is very important, especially when working with an oil-based polyurethane.
It has a strong odor and may produce exotic fumes. Breathing in such air may burn your throat and cause dizziness.
- Safety goggles. Polyurethane can irritate your eyes. Always wear a pair of safety goggles to ensure no tiny drops or splashes are in your eyes.
- Ventilation. Ensure that you are working in a well-ventilated area to prevent fumes from building up within your work environment.
The ventilation will facilitate proper breathing and faster drying of your projects.
- Clean up. Do a thorough cleaning after working with polyurethane. Leaving your cans open will increase the risk of a possible fire.
It will also allow fumes to escape into the air. Besides, you do not want to walk on a sticky floor because of that spill that you did not clean up.
- Paint thinner. Paint thinner is recommended, especially when working with an oil-based polyurethane.
You will likely spill some of your varnishes in unwanted areas around your project. A paint thinner or mineral spirits will help you remove the excess.
Also, take care while using them as they are highly flammable and can be hard to clean spills up.
Can You Apply Water Based Polyurethane Over Oil Based?
Isn’t it interesting how you can apply these formulas interchangeably?
This flexibility gives you immeasurable freedom as a woodworker. It allows you to work on new projects and renovate old ones.
If you find the oil-based polyurethane you have applied unappealing, you can always change it to water-based and vice versa.
We hope you enjoy your work as a woodworker as you switch between polyurethanes.
Whatever gives you the finishing you want, water- or oil-based poly, feel free to test both out.