Polyurethane is a class of plastics popularly used in home furnishings, beddings, and carpet setups. However, polyurethane coats only protect the layers beneath them once they’ve dried and cured, and this process takes time.
It takes between 24 and 48 hours for a polyurethane coat to dry before you can apply another one on top. Curing polyurethane typically takes between three weeks and a month, after which the surface is ready for use.
In this article, we’ll take a closer look at the drying and curing process, the types of polyurethane varnish available, and how to speed up the curing process if needed.
Polyurethane: Drying vs. Curing Process
Polyurethane is usually available as a varnish, which you use to coat wooden surfaces to make them waterproof and durable for use. However, just application isn’t enough to protect your surfaces – the material needs time to set before it can form a protective coating.
Drying
The drying time refers to how quickly polyurethane dries up, leaving a non-sticky surface to which you can apply another coat if needed.
The speed at which the coating dries will differ based on the type of varnish used. However, it will generally take a day or two, after which you should be able to walk on the wooden surface with socks.
However, drying alone doesn’t protect the surface from warping or getting damaged. Even if the first coat of polyurethane has dried, you should avoid placing heavy objects on the surface – doing this may result in the wood bending or becoming damaged in other ways.
Additionally, you want to avoid spilling any liquids onto the surface. If the polyurethane coat has only dried and not cured, the liquid could still seep into the wood below and leave permanent marks.
Curing
Curing is a lengthy process, and it can take between three weeks and a month for a polyurethane coat to properly cure. This extended period allows the polyurethane molecules to chemically interact with oxygen, resulting in a stronger molecular bond.
This means that the curing process allows your coats of polyurethane to bind strongly to the wood surface underneath, allowing it to offer protection from heat, pressure, and liquids.
When a polyurethane surface is cured, the wood is ready for use and can withstand furniture and heavy foot traffic without sustaining damage.
While it can be tempting to start using the surface once the last coat of the varnish has dried, it’s best to wait for a month until curing is complete. This will ensure your floor will be durable enough to last for years to come.
Does Oil-Based Polyurethane Need More Time to Dry?
While most people will use the most easily accessible polyurethane varnish to protect wooden surfaces, it’s crucial to remember that not all polyurethane is the same.
The type of polyurethane you use, combined with the quality of the wooden surface, temperature changes, and humidity, will determine the drying and curing time.
Polyurethane is a liquid plastic, and the varnish is made by dissolving the resin in a liquid solvent, like oil or water. This solvent is brushed or painted onto the wood and evaporates over time, leaving behind the polyurethane coating, which protects the wood.
While the potential combinations of wood, solvent, temperature, and other factors are limitless, there are two types of polyurethane you should know of when working with this material — oil-based and water-based.
Each of these coatings has its pros and cons, and you should assess your needs carefully before determining which is best for you.
Water-Based Polyurethane
As mentioned, water-based polyurethane is the type where water is used as a solvent for the resin. Water-based polyurethane has a much quicker drying time, often allowing you to apply a second coat within two hours of applying the first.
This type of polyurethane coating is also odorless, making it possible to apply the varnish even if you do not have adequate ventilation in the area. You should be able to lightly sand the surface within a few hours of application, as the solvent (water) evaporates quickly after application.
That said, it’s crucial to remember that while this coating dries quickly, it still takes at least three weeks to cure.
Water-based polyurethane sets quickly and doesn’t turn yellow with age, making it the ideal option for most households. However, the flip side is that this type of coating is less durable and unsuitable for high-traffic areas, so if you’re looking for a polyurethane coating for a commercial space, this isn’t the right option for you.
- Protects indoor wood surfaces such as furniture,...
- Water based formula dries fast and cleans up with soap...
- Dries to the touch in 30 minutes with coverage up to...
- Durable formula provides outstanding stain and scratch...
Oil-Based Polyurethane
Oil-based polyurethane takes longer to dry and cure, with the quick-dry versions taking between four and six hours to dry. However, most oil-based coats take at least twenty-four hours to dry before another layer can be applied (though it’s always best to wait at least forty-eight hours).
When applying oil-based polyurethane, you’ll need a well-ventilated setting to ensure the chemical odors don’t cause harm. Oil-based polyurethane requires a minimum of thirty days to cure (the longer, the better) and offers a durable finish if allowed to set correctly.
Oil-based polyurethane is more resistant to changes in temperature, moisture, and liquid spills. The only drawback is that this type of finish ‘yellows’ with age, which may ruin the aesthetic of a space.
- Protects interior wood surfaces such as furniture,...
- Oil based formula provides maximum durability and...
- Dries to the touch in 2 hours with coverage up to 150...
- Unique formula provides outstanding stain and scratch...
Factors That Affect the Drying Time of Polyurethane
We’ve established that oil-based polyurethane takes longer to dry. However, there are other factors that affect the drying time of polyurethane.
Temperature
Polyurethane dries best between 70°F and 80°F (21°C and 27°C). Keep in mind that while it’s possible to control the temperature at home, it’s challenging to do so in a garage or workshop, so you may not be able to control how long it takes to dry.
Higher temperatures will cause the coating to dry by increasing the rate of evaporation, while lower temperatures prevent the solvent from evaporating, slowing down the drying time.
Humidity
Water-based polyurethane should ideally be applied when there is 50% humidity. If you’re using an oil-based option instead, humidity should ideally be 70%.
That said, you may not be able to control humidity as well as you do temperature. An easy rule of thumb to keep in mind is that the more humid a space is, the longer polyurethane will take to dry.
Ventilation
While it’s crucial to control humidity, it’s also imperative to ensure adequate ventilation in the area – this isn’t just a safety precaution when using oil-based polyurethanes, it also ensures that any polyurethane coating you use dries quickly.
For good ventilation, consider keeping the windows open and allowing plenty of fresh air in. However, keep in mind that this will also allow dust or dirt from the outside to seep in and settle on your coat, which you’ll need to clean before applying the next coat.
Wood Absorbency
Wood, like any other material, is made up of cells and absorbs liquids that are poured onto it. However, there’s a limit to how much liquid can be absorbed before the wooden surface is saturated.
As such, polyurethane will dry at a different rate depending on how saturated the wood is. If you’re using new wood that hasn’t been dried yet, the coating will take longer to set. This extended drying time is because there’s already moisture in most cells on this wooden piece.
On the other hand, dry wood will absorb the polyurethane much quicker, significantly reducing drying time. Of course, this will only happen with the first two or three coats, after which the cells will be more saturated and slower to absorb the liquid.
Thickness
While it’s pretty obvious, it’s still worth mentioning here.
The thickness of the coat will play a role in the drying time. A thicker coat will take longer to evaporate, causing the finish to settle later than it would with a thinner layer. The thickness of the coat can be controlled, so it’s worth keeping in mind when applying a coat. However, if you opt for thinner coats, you may need to apply more coats until your surface is as protected as possible.
Sheen
Polyurethane coatings are available in different types of sheen, with each of these types taking a different amount of time to dry. The four most common types of sheen are:
- Matte
- Satin
- Semi-Gloss
- Glossy
Matte and satin finishes take less time to dry, while semi-gloss and glossy finishes take longer to dry, regardless of which type of polyurethane you use.
How to Speed Up Polyurethane Drying Time
Now that you’ve taken a look at the different factors that affect the drying time of polyurethane, here’s how you can help speed up the drying process.
Control the Temperature
If you can regulate the temperature in the drying area, you can help speed up the process. Ideally, maintaining a temperature of around 70°F (21°C) will ensure your polyurethane coating dries faster.
You could even turn the temperature up a notch – however, make sure you don’t go too high. Very hot temperatures can also adversely affect the drying process. That said, even something as simple as choosing a warmer day to apply the finish will help speed up the drying time (though you may want to avoid applying polyurethane outside at the height of summer, of course).
Open the Windows
Opening the windows in the area will help regulate humidity and provide ventilation to the coating, which is essential for the surface to dry quickly. If you’re concerned about dust and debris affecting the coating, consider using a fan to blow air across the room instead.
That said, while a fan will help speed up the drying process, it can also stir up dust that is already in the room and cause it to settle on the wet coat. So, you should ideally make sure your room is as clean as possible before starting polyurethane application.
Use Dry Wood
If you’re looking to dry your polyurethane coats as quickly as possible, one easy option is to use dried wood for the surface, as this will quickly absorb the coating as fast as possible. That said, this option is only feasible if you’re building something from scratch – if you’re coating an existing surface, you won’t be able to control what type of wood was used in its construction.
Apply Coating With a Roller
As mentioned earlier, the thickness of the coat plays a crucial role in determining the drying time, and the thicker the layer, the longer it’ll take to dry.
To ensure you don’t lay it on too thick, consider using a roller instead of a brush to apply the varnish. A roller will apply the coat evenly and consistently across the surface, ensuring a quicker drying process.
Note: While drying can be sped up, it’s crucial to adhere to the necessary curing time before you start using the surface in question.
How to Determine the Number of Polyurethane Coats to Apply
The number of polyurethane coats you apply will depend on various factors, including the type of solvent used, the time you have to complete the project, and whether the project is indoors or outdoors.
There’s typically a small window of time when you’ll be able to apply the second coat. For water-based solvents, that’s usually between two to three hours after applying the first coat, and for quick-drying, oil-based solvents, it’s between six and twelve hours.
If you apply the second coat too early, it’ll ruin the consistency of the first coat, and if you use it too late, it won’t blend correctly with the first.
If you’re using oil-based solvents, you’ll need to ensure you have enough time to complete the project, as there will be longer intervals between each coat. Additionally, if your project involves coating an outdoor area, you’ll need to be careful and ensure the first layer isn’t ruined by rain or excess sun before applying the second layer.
Ideally, you’ll need three to six coats of polyurethane to provide the smooth finish and protection you’re looking for. However, beyond that, you can decide on the number of layers based on the type of solvent you use, where it’s being applied, and the time frame you have in which to complete the project.
See also: What Kind of Paint Will Stick to Polyurethane?
More FAQs About Drying Polyurethane
How Do You Know When Polyurethane Has Dried?
To know whether your polyurethane coating has dried, wait until the surface no longer has a “wet,” tacky look to it. Once the surface looks dry visually, you can check by gently rubbing a finger over the surface. If liquid sticks to your hand, the coat has not dried yet.
If it doesn’t stick, the polyurethane has dried, and you can now apply an additional coat (or leave it to cure).
Why Is My Polyurethane Coat Not Drying?
Your polyurethane coat may not be drying due to several factors:
- The temperature may be too low. Temperatures around 55°F (13°C) and below will prevent the coating from drying at all.
- Not enough ventilation. Closed-up areas aren’t ideal for drying polyurethane finishes as there’s no ventilation available.
- The coat may be too thick. While your coating will eventually dry, an excessively thick coat can prevent the first layer from evaporating entirely, leaving the surface tacky and sticky.
- The wood may be naturally oily. Some wooden surfaces contain natural oils that prevent the coating from seeping into the cells, which can impede the drying process.
Final Thoughts
Polyurethane coating is an effective way to protect wood and furniture against damage from moisture and heat. There are a number of factors that will determine how long it will take to try, including the type of polyurethane you use, the temperature, and the humidity.
In general, each coat will take 1-2 days to dry. Once the final coat is applied, the polyurethane will take another 3-4 weeks to cure fully.
Related post: How Many Coat of Polyurethane on Wood Floors?
