How Long Does Polyurethane Take To Dry? (Oil and Water-Based​)

Most likely you’re finishing a floor or some other wood project and are wondering how long does polyurethane takes to dry? Like most simple questions, the answer is a bit more detailed. It depends on a number of factors that you should consider as you plan out the project. The principal variables are what kind of polyurethane are you using and how warm the room is among other things will determine dry time.

It takes oil-based polyurethane 24-48 hours and water-based polyurethane 6 hours to dry enough to be able to walk on it in socks and proceed to the next step of the application process. Don’t confuse dry time with curing time which can take up to 1 month depending on conditions.

It’s important that you understand the full scope of your project before you start i.e. how many coats of polyurethane do you plan to apply, or do you expect to sand the floor? 

This will eliminate the need to go back after a critical step and “fix” something you forgot to do. You can use these “rules of thumb” to plan your project:

Oil Based Polyurethane Drying Time and Curing Time 

For an oil based polyurethane, you can walk on floors after 24 hours. The floor should “look” dry and not be tacky to the touch. Keep pets off and walk on the floors wearing socks. Don’t wear shoes and don’t walk in bare feet. After 24 hours, you can then start sanding if you intend to, or you can add another coat.

48 hours after your last coat you can walk on the polyurethane with shoes and it should not feel tacky. After 4 days it will be totally dry. Keep your animals off of any polyurethane for at least 2 weeks. After a full 30 days oil based polyurethane will be completely cured.

Water-Based Polyurethane Drying Time and Curing Time 

A water based polyurethane should be dry enough to walk on with socks after 6 hours. At this point it should look dry and not be tacky to the touch. You still want to keep your pets off of it and only walk on it with socks. If you plan on sanding it, now is when you can start, or you can add another coat of water based polyurethane.

After 24 hours your water based polyurethane will be dry enough to walk on. After 48 hours it will be totally dry, but you want to keep animals off of it for at least a week. You also want to make sure you leave the polyurethane uncovered for 2 weeks. After 30 days your water based polyurethane will be fully cured.

Polyurethane Drying vs. Curing

There are two phases to applying a polyurethane finish to a floor. Drying time is the recommended duration needed between coats. Curing time is the recommended length of time before using it. Keep in mind that each manufacturer produces a range of finishes each with a secret recipe with different additives and chemicals affecting the application, the behavior of the product while you’re applying it, and the result. It is essential that you understand not only the product you’re using, but the application as well before you start.

Drying Polyurethane

The first phase is the “drying” phase. When you apply polyurethane to the floor, you’re applying a layer of polyurethane resin in a liquid solvent, to the floor. The resin is what remains after the solvent dries and is the material that forms the final barrier protecting the wood. The solvent can be either water or some type of finishing the oil, e.g. linseed, tung, or walnut oils. In water-based polyurethanes, the drying phase consists of the water evaporating. In oil-based polyurethanes, the finishing oils evaporate. Water simply dries faster than the oils or solvents.

Curing Polyurethane

The second phase is the “curing” phase. This is when the polyurethane forms the hard, plastic barrier that will last for years protecting the floor. Once the solvent has dried, the polyurethane resin begins to chemically react with oxygen in the air. The oxygen reacts with the polyurethane cross linking the polymer molecules and forming a three-dimensional matrix of the resin.

Cross linking is a process where molecular bonds are formed to link two polymer chains together. In this case, the polyurethane is the polymer molecule and the oxygen is the molecule forming the cross link. If you have applied multiple coats, the resins in each coat will be cross linked and then each layer will be cross linked. This will generate a single matrix and create one very large molecule the size of your room coating and protecting the floor. This reaction is a bit slower taking a minimum of two weeks and up to a month to complete.

Factors Affecting Polyurethane Drying and Curing

Every project is unique. The length of this type of project is measured in days and weeks instead of minutes and hours. When you’re planning how you’re going to approach your project, keep in mind that the “rules of thumb” listed above are affected by a host of variables:

Starting Surface

Raw, sanded wood will absorb the first coat and will shorten the dry time. The first coat wets and seals the wood. Each subsequent coat consists of applying one layer over an existing layer of polyurethane and will take longer to dry.

Type of Wood

Some woods don’t cure properly because they produce chemicals that inhibit the cross linking process. Rosewoods and some aromatic cedars are included in this category.

Type of Polyurethane

Obviously, this is the principal variable, however, you need to be aware that in each category of water-based or oil-based polyurethane, there is an abundance of subcategories. Some manufacturers add drying agents. Some add oil and possibly other solvents. You can get stains to add color and the list goes on. Each component may impact the dry and cure time by a little or it may force you to change your entire approach. Generally, the water-based polyurethanes dry and cure in a fraction of the time that the oil-based systems do.

Temperature and Humidity

The times stated above are based on a 70°F (21°C) day and 70% humidity. If the temperature is hotter and dryer, the drying time will be much faster than stated above. Conversely, a cooler temperature on a wet day could extend the drying time by as much as half a day.

Mixing Polyurethanes Types

Mixing polyurethanes is complex. Remember you’re trying to form a single large molecule. If you are using one type of polyurethane with the same kind of solvent or oil, the chemical reaction turns out to be straightforward without a lot of mitigating factors. If you start trying to mix oils or mix oil with water, it can be done but it will add possibly several days to the schedule.

Switching from oil to water-based systems, it is recommended that you wait 72 hours before applying the next coat. Switching from water to oil-based systems, it is recommended waiting only 24 hours. The point of waiting is to ensure the first coat is completely dry before introducing a solvent that may not be compatible with the previous coat.

How The Polyurethane is Applied

If you apply the polyurethane by brush, the layers will be thicker than if you spray it on or if you’re applying it and then wiping it off (a technique used in woodworking). A thicker layer of polyurethane will take longer to dry, so you can expect a job done with a brush to take a little longer to dry.

Polyurethane Safety

So, is using polyurethane safe? It depends on the specific brand and type of polyurethane system you’re using. Before using ANY chemical, read the instructions and pay particular attention to the safety precautions!

While the polyurethane is drying and curing, oil-based systems smell a lot worse and contain chemicals in the solvent that can be harmful to your respiratory system. Water-based polyurethane doesn’t smell as bad as the oil-based systems, but the cautions still apply. If you have asthma, bronchitis, or some other respiratory condition, be aware that drying or curing polyurethane generate fumes that can irritate these issues. Once the floor is fully cured, there is no further cause for concern.

Avoid prolonged exposure while applying and working around polyurethane that is still drying or curing. Make sure the area is well ventilated. It will also help to wear a mask while you are working with polyurethane.

Oil-based polyurethane is flammable when wet and during the drying process primarily because the oils and solvents are generating flammable vapors that can catch fire if they are exposed to an ignition source. This applies to wet rags used to wipe up any liquids. Water-based systems are not flammable.  So avoid smoking or activities that could potentially generate sparks. If using oil-based polyurethane, consider having a fire extinguisher handy. Always follow directions.

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