Polyurethane finish is one of the highly durable coatings that is used in furniture making, retouching a boat, or constructing cabinetry. The sealant is easy to apply and it’s resistant to heat, chemicals, and wear and tear such as scratches.
The only problem that occurs with polyurethane is when it becomes soft and tack instead of drying on the wood surface. While it certainly can be annoying, depending on circumstances it may take a polyurethane finish several hours, if not far longer to fully dry.
Why is Polyurethane Sticky?
There are several reasons why this may be happening. Let’s address them one by one and know about the possible fixes that can ease the complications.
1- Too Thick a Coating Has Been Applied
One major reason why the polyurethane is not drying is due to a thick coating that has been applied incorrectly. The best way to apply a coating of polyurethane finish is to do so in thin layers using a poly brush which is generally a natural bristle or a synthetic brush.
You may feel the need to apply a thicker coating, but that will take considerably longer to dry. To leave the non-sticky layer, it is far better to apply a thin coat, let it dry, and then apply another thin coat which should dry even faster compared to the first.
2- Cold Room Temperature & Poor Air Circulation
A cold room with still air means it will take far longer for the liquid inside the polyurethane finish to evaporate away. Ways to combat this are to open a window, turn on a fan, and use a heater to warm up the temperature in the room itself.
Remember not to have the fan directly blow onto the finish as small dust or dirt particles might become embedded. Instead, open a window or door on at least two sides of the room and place the fan facing outwards. This will effectively move the air inside the room.
3- Wood has Natural Oil
The natural oil found inside the wood can greatly lengthen the time it takes for the polyurethane finish to dry. This means that the polyurethane will eventually dry as it covers the natural oil, but it may take longer than the average time listed on the product.
You can feel the natural oil in most woods, particularly the exotic timber with the exception of mahogany.
Keep in mind that mineral spirits are present in the polyurethane which will act as a solvent for the resin of the wood. But this will still affect the drying time of the first coat of finish that you apply.
However, once the first coat dries, the second coat will not take nearly as long since it is separated from the natural oil of the wood.
4- Polyurethane is Past Its Shelf Life
Although polyurethane finishes can sit on the shelf for a good decade under proper conditions, they can still congeal within the container and become worthless.
If you open a can of polyurethane finish and it is gummed-up, gunky, or congealed, it is best to throw it away. While you can use mineral spirits to loosen up the ingredients, that will often not work very well to bring back the finish.
To extend the time your polyurethane finish can last on the shelf, be sure the container is air-tight and stored in a cool, dry place that is not in direct sunlight.
5- Not Enough Time has Passed
You can always wait longer for the polyurethane finish to dry even if it seems the wait time is unreasonable.
But before doing that know what type of polyurethane finish is being used and under what conditions, to get a decent estimate of the time it normally takes to dry.
There are two basic types of polyurethane finish, oil and water-based. While water-based polyurethane finish is clear, oil-based finishes will have an amber accent to them.
Another difference is the drying times as oil-based products can take considerably longer compared to water-based versions.
Under average conditions, a water-based polyurethane finish will take five hours to dry, give or take an hour, and up to two weeks to fully cure. Whereas an oil-based finish will take up to a full 24 hours to dry and a month to fully cure.
So, for using or before putting light foot traffic on the polyurethane-coated surfaces you should at least wait for a full day (24 hours).
How Do You Get Polyurethane to Dry?
The first method to try when polyurethane won’t dry as expected is to turn up the heat, especially if the room you are working in is cold. Be sure it is dry heat as added moisture will only lengthen the drying process.
Break Out the Hair Dryer
A hairdryer applies dry heat, which makes it perfect to speed up the drying time of your polyurethane finish and your hair as well.
However, unlike your hair which dries quickly, it will take far longer for the hair drying to work on your sticky polyurethane finish.
You will need to go over it, section by section, which may take some time. Plus, there is the chance that you will kick up some dust or dirt that will embed in the finish itself.
If you have one spot on the project that is still tacky, then applying a hair dryer to that spot will speed up the drying time. Otherwise, there are faster methods available.
Set Your Thermostat and Dehumidify the Room
Another method you can use to reduce the drying time is by removing the moisture in the air and turning up the thermostat a few degrees.
Ideally, a quick-drying polyurethane finish should be in a room that is set at 77 degrees F. Getting within a degree or two of that temperature will lessen the drying time.
A dehumidifier will also work quite well in lowering the humidity levels so the finish can dry faster.
Can You Help Polyurethane Finish Dry Faster Under Sunlight?
Polyurethane finishes will not be affected in terms of the light but may be affected by the heat that is generated.
However, you want to keep the finish out of the sunlight because of the ultraviolet or UV rays that can damage the Varathane polyurethane coating and cause it to fade.
Of course, there are polyurethane finishes that have UV protection built-in, but it is still advisable to keep the finish out of direct sunlight anyway.
How Long to Let Polyurethane Dry Between 2 Coats?
It will typically take between 2 to 4 hours for a water-based polyurethane and between 6 to 10 hours for an oil-based polyurethane to dry before you can put up a second coat on your wood furniture or flooring.
With that said, keep in mind that the curing time for polyurethane will essentially be higher and it should take around 30 days to completely get cured before you can say it has reached its full hardness.
My recommendation for a DIY poly job is to allow about 24 to 48 hours between coats, sand it carefully with a wood sander after the first coat, and then apply a thin layer of the second. You may add third or additional layers; but, generally, two coats are enough.
The final coat of polyurethane should not be sanded but allowed to dry and cure into a hard protective finish.
So, why is your polyurethane sticky, how to fix and can you speed up polyurethane’s drying time?
Perhaps a better question is whether you should speed up the drying time at all.
It’s a good thing to open two windows and place one fan facing outward to increase the airflow.
But specific methods such as a hair dryer may waste more time and electricity than it is worth. Plus, if the polyurethane dries too quickly it may crack which means you are only adding time to sand and refinish the surface.
So, if you are worried about polyurethane not drying or taking too long to dry – it is best to purchase a fast-drying polyurethane finish and gently increase the airflow into the room for the best results. This will be far better than fixing the poly mistakes like bubbles later on which could take tons of time and effort.
Jack Luis is a semi-retired painter who loved painting his clients’ ideas on their walls.
He had worked as a painter for over a decade serving customers in areas such as Charleston, Mount Pleasant, Beaufort, and Georgetown, SC (South Carolina). Today in his free time, he likes to read and write about the newer techniques implemented in his profession. You may read more about him here or get in touch with him here.