Are you new to the DIY floor varnish club? Here you’ll get information on all things related to polyurethane coatings and varnishes.
Whether you are a seasoned woodworker or just starting a home improvement journey, you are sure to stumble upon polyurethane coating solutions more than once. This is because polyurethane is a perfect finishing product for wooden surfaces.
If you have questions like, “How long does it take to dry?” read this piece till the end, and you’ll have many similar queries resolved. We will talk about types of polyurethane, kinds of finishes, drying and curing time, along with valuable tips for getting the best out of polyurethane.
So, let’s begin.
How Long Does Polyurethane Take To Dry?
In short, polyurethane takes 24 to 48 hours to dry and 25 to 30 days to cure completely.
Types Of Polyurethane Sealers
All polyurethane coatings or varnish are made of fine polyurethane resins, which can be dissolved in a liquid. You can think of it as a liquid plastic that can be spread on flat surfaces to protect from water, heat, dust and microbes.
There are various types of polyurethane coatings available nowadays, but we can generally classify them into two types – water-based and oil-based polyurethane. Even though both of them provide the same functions, they vary in drying and curing time.
So before discussing the drying time, let’s take a look into the characteristics of the two main categories.
Water-based polyurethane is considered to be the safer option between the two since it does not contain any VOCs. Since they don’t produce strong, headache-causing odors, they are much easier to work with. Generally, the solution is much thinner; thus, the coatings are paper thin too. Due to the lightweight solution, it doesn’t take long to dry and cure.
Another factor that increases the drying time is the presence of water in the mix. As the water evaporates, it leaves only the polyurethane resin on the surface. However, to get an even finish, this type of sealer requires more layers as compared to oil-based polyurethane. Moreover, water-based polyurethane dries off clear and tends to fare better in the long run.
On the opposite end of the spectrum is oil-based polyurethane. These provide comparatively thicker coatings due to their robust formula. The downside of this dense and oily formula is that it doesn’t dry off easily. When it comes to safety and toxicity, they are safe to use for floorings and furniture; however, they do contain VOCs.
Volatile organic compounds in large quantities can be harmful to human health. It can cause respiratory symptoms like runny nose, itching in the throat, sneezing, and skin rashes if precaution isn’t taken. These compounds and the oily solution combine to produce a strong odor which is unpleasant to be around and can even cause headaches.
Also, after a few years, you will notice the varnish change to a darker yellowish color which is not the case with water-based polyurethane. We will discuss in detail about the two types of polyurethane and their drying and curing time in the following sections. So make sure you read till the end.
Type Of Finish
Apart from the base of the polyurethane product, features like types of finishes are a contributing factor to the drying time. There are 3 different types of finishes available – high gloss, semi-gloss, and satin finish. Take a look at the 3 types because all of them have a different drying time.
This finish gives a sleek and shiny look to floors. It’s suitable for hardwood floors and is resistant to scratches and water damage. They are often used in living rooms or even on wooden surfaces outdoors for their glossy look. Often you will find that these finishes stay longer and retain their gloss for a significant time.
Semi-gloss polyurethane is quite versatile and durable. This is why it is often found on furniture, cabinets, doors and intricate wooden artwork. One benefit of semi-gloss is that it dries faster than high gloss polyurethane. This type of finish does provide some shine, but it doesn’t match the slick look of high gloss options.
Satin finishes in polyurethane products do not provide any sheen or gloss to surfaces. In fact, they look almost like matte-finish most of the time. The little shine they have is subtle, making it look fresh, but otherwise, they have a unique appeal. These types of finishes are the fastest drying polyurethanes available.
Polyurethane Drying Time
Now the question arises, how does one know when polyurethane has dried? Take a look at this table to get a fair idea of the difference between water and oil-based polyurethane drying times.
|Water-Based Polyurethane||Oil-Based Polyurethane|
|Time for next coat||7 hours||24 hours|
|Dried enough to touch||24 hours||48 hours|
|Add furniture||2 days||4 days|
|Add rugs and mats||1 week||2 weeks|
|Completely cured||25 days||30 days|
Drying Time For Water-Based Polyurethane
Water-based polyurethane coating dries up quickly; in fact, they need merely 5 to 6 hours to dry. After 7 hours of applying the first coat, you can walk on the sealed floor without causing any damage. But remember to wear socks while walking because friction and dust from your bare feet might ruin the finish.
If you want to add the next layer or a finishing topcoat, you can do that after 7 hours of drying. After the 24-hour mark, you walk on the varnished floors with shoes as well. As far as moving furnishings into the room is concerned, keep a gap of 48 hours after the last coat to shift anything bulky in.
Pets and children should not be allowed in the room for at least 3 days. There are two reasons for this – one is for their safety, and the other is to ensure the varnish is maintained without scratches and marks.
Drying Time For Oil-Based Polyurethane
As we mentioned earlier, oil-based polyurethane takes longer to dry and cure. After application, it is recommended to keep the surface off-limits for at least a good 24 hours. If you have varnished a hardwood floor, you can attempt to step on it after 24 – 48 hours, but don’t walk in with shoes or barefoot. Instead, wear a clean, dry pair of socks for inspection.
It goes without saying that you should keep children and pets away from the freshly varnished surface to prevent any interference in drying. After the 48-hour mark has crossed, the coating should be completely set, and you can take a walk on the floors with your shoes. Wait for another day to add the furniture back since dragging heavy things might damage the finish.
After two weeks or so, it is safe to bring in rugs and floor coverings. However, these are ideal recommendations that might not be necessary for all projects like wall or furniture coatings.
Note – These estimates are primarily valid for a moderate climate. If the humidity of the room is high or there is dampness and moisture accumulation, the drying time will significantly increase. Turning on an air conditioner or dehumidifier of increased ventilation may be required to speed up the process.
How Long Does Polyurethane Dry In Layers
Generally, no one applies only one coat of polyurethane. Even the thickest oil-based varnishes need two or three layers to settle in and show any kind of long term effect. Now, the first layer is the simplest, you just have to ensure the surface is sanded and bits of dust are thoroughly removed by vacuuming.
Next, apply the first layer in a thin coat and wait for it to dry. Once the coating is dry to touch without any stickiness or wetness, it is ready for the second coat. The surface does not need to be cured entirely for the next coat; surface-level drying is enough for the second and third coats.
Difference Between Drying And Curing
Now, there is a difference between drying and curing polyurethane coatings, even though these terms are often used interchangeably. While we discuss drying time, it is essential to understand the definition of drying and curing when it comes to polyurethane.
A coating is said to be dry when the external polyurethane hardens. At this stage, the varnish is no longer wet, sticky or tacky. However, the surface is not ready for use yet because the coating is prone to wrinkling, imprinting, and forming scars even at this stage. If too much pressure is applied, the smooth finish can be ruined easily.
And for curing, we call a surface wholly cured when the polyurethane resins have completely hardened (not just the surface). This happens when varnish has been exposed to oxygen, creating a chemical reaction that causes the hardening of the resins in the coating.
This is the final stage of any application process, and the floor is ready to use after curing. Often, it can take up to a month to completely cure a floor.
Now that we understand what curing is, you might be wondering how long it will take to cure floors and walls.
As we discussed earlier, we know the time required to dry and cure. However, there are certain aspects that we cannot ignore when it comes to a complicated process like drying polyurethane. Take a look at some of the factors that influence curing time.
Factors Affecting Curing Time
Type Of Polyurethane
Since water-based polyurethane solutions tend to be thinner as compared to oil-based ones, they are sure to dry much sooner. If the project needs to be completed within a time limit, water-based ones are your best bet as you can get many layers in little time.
A room humidity percent of 50 – 70 is good enough for drying and curing usually. If the moisture happens to be too high, the varnish may not dry easily and will end up damaging the result. If your room suffers from high humidity levels, there are a few actions you can take to counter the effects.
Firstly, you can opt for oil-based polyurethane since water-based ones are more prone to damage by moisture. Secondly, you can install a dehumidifier in the room to help the coating dry quickly.
External temperature is one of the most critical factors which can change the drying and curing time. Ideally, a room temperature of 70 degrees Fahrenheit is perfect for optimal curing. If the temperature drops too low or near the freezing point, the polyurethane coating will take far too long to dry.
Also, if drying at a cold temperature, you will notice a thin whitish layer will develop on the surface, which needs to be avoided. And if the room temperature is too high, it shouldn’t have a problem curing, but the smooth finish might be compromised due to extra heat.
Number Of Layers
Before starting the application, you’ll need to calculate how many layers are required for your flooring. Of course, if you opt for a water-based polyurethane, the number of layers needed will go up. Besides this, the thickness of coats will heavily influence the drying time.
If you use a brush to apply the varnish, the layers tend to be thicker than foam rollers. So, if you want to keep the layers thin, opt for rollers or sprays, which will save a lot of drying time.
This factor might be overlooked often because not many people are aware of the type of flooring. Essentially, if you have hardwood floors, then there can be a variation in drying and curing time depending on the type of wood.
Certain wood types like cedar and rosewood have chemicals that do not allow the complete chemical reaction required for layering. Any kind of interference in the chemical process will increase the time necessary to dry.
The starting surface needs to be spotless. The first step is to sand the floor to remove unwanted bumps, to create an even canvas for applying varnish. An adequately sanded wooden surface can absorb the polyurethane solution quickly and thus allows for quick drying and curing.
Tips For Drying Polyurethane Coatings Faster
There might be occasions when you are running short on time or don’t have the patience to wait for weeks for the coatings to dry. In such circumstances, there are a few methods that can help to increase the rate of drying. Let’s see what these tips and tricks are –
Add A Thinner
A simple solution for thick polyurethane coating is to thin it down using solvents. You can add naphtha to the polyurethane solution because it helps the coating to dry faster. Naphtha has a higher evaporation rate than spirit or turpentine, making it an excellent choice for thinning varnishes.
Once you add the thinner, mix it well and pour it from a height to understand the consistency. It should be fluid and run efficiently. This lighter solution will not hold well on brushes, so a foam or sponge roller will be required to spread it across the surface. Try this method and see for yourself how much quicker the coating tends to dry.
Polyurethane does not handle cold temperatures very well. It’s not like the coating will get damaged by low temperature, but the drying time will become prolonged. This is especially true in frigid climates without a heating system or coating the floor during the winter season.
To overcome this issue, people use artificial heat to warm up the room to assist in drying the polyurethane quickly. While some people use powerful hairdryers, others use portable heating devices or heating lamps.
Do note that these methods are effective for drying the varnish speedily but not for curing it. The speed at which the floors cure cannot be increased even with artificial heat assistance.
Similar to low temperatures, humidity also increases the hours required for drying. One of the many solutions to this issue is to use a dehumidifier in the room. After the coating for the entire floor is complete, you can bring in a dehumidifier and suspend it from the ceiling. It could even be attached to the walls to work overnight and remove the excess moisture from the air.
Even an air conditioner can do the same job. Set it at low humidity adjustment at room temperature, and it works just as well. If you know the humidity in the home is always on the higher side, you might want to consider the oil-based options. This is because they do not get affected by moisture in the environment the way water-based ones do.
Apply Thinner Layers
Applying thin layers will definitely save you a few extra hours of waiting for the floors to dry. It would help if you used a larger roller that can be dipped in the pan holding the varnish. This kind of tool will ensure you cover a large area at once. Apart from that, you can also remove the excess coating by running a dry roller over the floor.
Prepare The Surface
Even before you open the polyurethane can, the floor should be sanded and vacuumed. You can use any kind of sandpaper to flatten the uneven pieces of wood which might be sticking out. Then grab a vacuum and remove all the dust and debris. Once this is done, your surface is ready for the first coat of polyurethane.
Taking these efforts are essential because smooth and clean wooden panels allow the polyurethane to adhere readily. And this step will noticeably reduce the drying time.
The drying of polyurethane was one topic we really wanted to address because so many people seem to be confused about how to use them. Many people new to DIY home improvements also had requested for drying times of different types of polyurethane.
We hope we were able to resolve all your questions related to drying and curing polyurethane. If you have any further queries or would like to give a few suggestions of your own, the comment section is always open.
That being said, coating and varnishing your own home should not be a daunting task. Just skim through this article whenever you get stuck with applying polyurethane to the floors, and you’ll get all needed for the next project.
With that, we take your leave, bye!
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