Woodworkers know polyurethane to be a good choice for finishing your home shop project, whether it’s a piece of furniture or a new floor in the kid’s bedroom. It is one of the most common wood finishes used today, and for good reason. We have either written about it specifically or at least mentioned it in past articles, here and here.
It’s a heat-resistant finish composed of polymers (plastics) and urethane. A liquid plastic, a specific type of polymer, used as a wood finish that dries to a solid plastic sheet. It is what is called a film finish – it does not sink into the wood – that sits on the wood surface and provides water-proof protection.
The previous articles we’ve written on the subject have pertained to a water-based polyurethane. However, there is also an oil-based polyurethane. The oil-based product will last longer than its water-based relative, has a distinctive odor when used that requires a respirator when applied, and will take 2-3 times as long to dry between coats.
Therein lies the issue for impatient woodworkers. Whether it’s on that piece of furniture or the refinished floor, drying time can become a frustrating point. If time is your enemy in the project, there are some pretty straightforward and obvious ways to speed along the drying process.
Water-based: 8 hrs between coats, 24 hrs dry to touch, 2-3 days ready to use, and full cure in 20 days.
Oil-based: 24 hrs between coats, 48 hrs dry to touch, 4-5 days ready to use, and full cure in 30 days.
While these dry time and cure time frames can be sped up, there is no magical trick for doing so. Although some suggest the addition of naphtha to polyurethane will speed up these times, this is a false premise. Don’t waste your time (pun intended) with this suggestion.
Many woodworkers prefer to use an oil-based polyurethane, believing it to look better than the water-based option. Even though the chart above suggests a much longer drying time, there are some steps you can take to reduce the dry time:
- Use a High-Build Polyurethane. For instance, Minwax High-Build Polyurethane is a clear, oil-based product that is specifically designed to provide a durable, long-lasting finish with just 2 coats. It is suitable for any of your likely home projects – furniture, kitchen cabinets, floor refinishing. In and of itself, it doesn’t necessarily speed up the dry time, but it does reduce the number of coats that will need to dry.
Another product along similar lines is Rust-Oleum Varathane Triple Thick Polyurethane. This is a water-based product that will provide a one-coat coverage that will dry within 2 hours of application.
- Use a Fast-Drying Polyurethane. Another Minwax product, Minwax Super Fast-Drying Polyurethane For Floors, is also an oil-based finish specifically designed for use on hardwood floors. Its optimized drying technology will give you faster second coat times. If you choose this option, be sure to apply a thin coat using a high-quality natural or foam brush and allow it to dry for 4-6 hours before sanding with a high grit sandpaper (220 grit) to give it a smooth and even finish.
What Will Help Speed Up Polyurethane Drying Time?
If the polyurethane on hand is neither a high-build nor a fast-drying product, though, what other steps can you take to move the dry time along?
Environmental conditions will have an effect on the dry time of your finish, as you might expect. The wood being finished may also affect the dry time, depending on the type of polyurethane you’re using. Natural wood oils and oil-based polyurethane could in combination increase the drying time of the finish, to be sure to consider this when choosing your polyurethane product.
Generally, though, there are some simple and obvious steps you can take to improve drying time, including:
- Ventilation. Humidity and stagnant air will contribute to a longer drying time for polyurethane application. With oil-based poly choices, there is also the odor problem and the need for a respirator during application.
Create air circulation by opening windows and doors, and use large floor fans to keep the air moving around your project. This will help speed up the dry time.
The use of a dehumidifier will also help. They are not expensive, and drying the air in the room will help dry the finish that much faster. Just be sure to remember the collection bucket will need to be emptied from time to time depending on the humidity level. Dehumidifiers are designed to shut off when the bucket is full, and if not attended to, the room’s humidity will not be reduced when it’s off.
- Heat. Higher temperatures, when not accompanied by higher humidity, will increase drying times for polyurethane finishes. Depending on the size of your project (a chair, or a cabinet, or a table top, but probably not a floor), a hair dryer could be used. For something larger, a heat lamp or space heater might be a better choice.
For an oil-based polyurethane, a higher ambient room temperature, generally, will help reduce dry time. A temperature of between 79 and 95 Fahrenheit, and with low moisture, will speed the dry time along for you.
Just remember, though, that increased heat to improve drying time will not change the curing time. The cure time numbers in the chart above will still apply (no pun intended).
There are a few caveats about improving drying times, as well, and they include:
- The sun. While heat from sunshine in warm weather will improve drying times, the sun will also harm the wood. While polyurethane provides a strong, durable, and water-proof finish on your wood, it does not protect the wood from harmful UV rays. It’s a clear varnish, and without a tint, the UV rays will harm the wood. So, don’t move your project outside on that sunny day thinking it will be the solution. Yes, the finish will dry faster, but the wood can be harmed in the process.
- Your impatience. If you have not allowed the first coat to dry sufficiently before applying the second coat, the accumulated wet polyurethane will just take that much longer to dry and you will be defeating your own purposes.
You also put yourself in the position of having to remove the second coat with a solvent such as a paint stripper or acetone in order to allow the first coat to dry fully before you try again. In these instances, refer back to the application of heat and increasing ventilation to then speed up the remaining dry time of the first coat.
On the subject of patience, remember how carefully you measured, cut and assembled. Your project has turned out as well as you had hoped. You’ve sanded and smoothed, and applied your stain well. If you’ve taken all that time to produce that piece of furniture, or install that new floor, or replace cabinet doors in the kitchen, just show a little more patience when applying your polyurethane finish.
In looking for a helpful video to recommend, we came across one that departs a little bit from some of the advice we offered about adding solvents to polyurethane to decrease drying time. The fellow who made the video ran his own test of adding mineral spirits to both Minwax Fast Drying Polyurethane, and an oil-based poly product.
By the way, we’ve written about mineral spirits previously, too, and you’ll find that article here.
General Rules of Polyurethane Application
As we have mentioned, you want to sand and smooth the wood surface well before applying the first coat of polyurethane. A rough or scratched wood surface will create a rough and uneven finish surface. The same holds true for cleaning the surface well before that first coat. If it’s dirty, you’ll have a dirty finish.
Assuming you’ve followed these rules, you’ll want to sand the finish between coats. A fine sandpaper, like 220 grit, should be used to sand lightly. It will remove any brush strokes if you’ve used a brush, and create another smooth and level surface for the second coat. If you plan on applying a third coat (not a bad idea), repeat this after the second coat. Be sure to clean the sanded surface of all dust, also.
If you follow these steps, the end result is a smooth final coat finish, just exactly what you were hoping for on your project.
Again, patience, and putting in the right effort so your project has that professional appearance with a great finish. Take your time, do what you can to speed up the drying process as we’ve presented here, but don’t skip any of the steps.