Before you can use a polyurethane sealed surface, the polyurethane must dry. So, how long does polyurethane take to dry?
Water-based polyurethane takes 8 hours to dry enough for a re-coat and 24 hours to cure. In comparison, oil-based polyurethane takes 24 hours to dry enough for a re-coat and 48-72 hours to cure.
However, the dry time of polyurethane depends on the temperature, humidity levels, the thickness of the coat, and airflow. Also, if you apply thin coats of polyurethane, the sealer dries faster.
There are a few tricks you can do to speed up the dry time of polyurethane. Check them out down below.
Polyurethane Dry Time Between Coats
Oil-based polyurethane must dry 24 hours between coats. In comparison, water-based polyurethane must dry for 8 hours between coats. The dry between coats refers to the time it takes polyurethane to dry before you can apply another coat.
Oil-based and water-based polyurethane have different drying times because they have different paint solvents. Oil-based polyurethane uses synthetic or natural oil as its solvent, while water-based polyurethane uses water as its solvent. Since water evaporates faster than oil, it means water-based polyurethane dries faster than oil-based polyurethane.
However, there are several types of polyurethane, and each type has a different drying time. For instance, satin polyurethane will dry faster than high-gloss polyurethane even if both sealants have the same base or solvent. That’s because the high-gloss polyurethane has more additives and gloss in the paint formula, and that increases the drying time.
You must wait for the polyurethane to dry before applying a new coat. If you re-coat too soon, the polyurethane will turn sticky. That’s because the solvent will be trapped between coats of polyurethane and won’t allow the new coat of polyurethane to stick. Since the coat of polyurethane won’t stick, the polyurethane will become tacky and peel off.
Polyurethane Cure Time
On average, water-based polyurethane cures within 24 hours, while oil-based polyurethane cures within 48 hours. The curing time refers to how long to wait until you can use and clean the polyurethane finished item.
There’s a difference between the drying time and curing time of polyurethane. Polyurethane dries through evaporation, while it cures through oxidation.
The solvent (water or oil) must evaporate for polyurethane to dry. However, for polyurethane to cure, the oxidation process must be completed.
Oxidization is a process where the chemical particles in the polyurethane coating react to the oxygen in the atmosphere. In simple words, when the polyurethane cures, the paint particles harden and bond together.
The polyurethane must cure before you use or clean it. If you clean a polyurethane coating before it cures, you will ruin the finish.
Speeding Up Polyurethane Dry Time
To speed up polyurethane drying time, you must increase the temperature around the paint coating. Here are 4 methods you can use to do it:
Method 1: Apply Thin Coats
Polyurethane has a thick flow; the thicker the flow, the longer the polyurethane takes to dry. However, polyurethane will dry faster if you apply thin coats. So, to speed up the drying time of polyurethane, thin it before applying.
To thin water-based polyurethane, use water. To thin oil-based polyurethane, use mineral spirits or turpentine. If you spray polyurethane, thin it with a ratio of 1:4 (1 part paint thinner 4 parts polyurethane). For a paintbrush or roller, thin polyurethane with a ratio of 1:3 (1 part paint thinner 3 parts polyurethane).
Once you thin polyurethane, apply it, and polyurethane will dry faster.
Method 2: Use a Hairdryer
Since polyurethane dries through evaporation, increasing the temperature (heat) around the paint coating will increase the evaporation rate. If the evaporation rate increases, the polyurethane dries faster.
Here’s how to use a hairdryer to make polyurethane dry faster:
- Plug in the Hairdryer – Turn on the hairdryer and set the temperature heat to medium.
- Move the Hairdryer Around The Polyurethane – Keep the hairdryer 8 inches away from the polyurethane coating. Move the hairdryer from one side of polyurethane to the other side. Don’t keep the hairdryer over the same spot for too long because the polyurethane will dry unevenly.
- Let the Polyurethane To Dry – You shouldn’t fully dry the polyurethane with a hairdryer because the polyurethane will dry too fast and peel off. If the paint particles harden too fast, they won’t bond properly, and the polyurethane coating won’t be durable.
You should use the hairdryer over polyurethane for only 5 minutes.
Method 3: Lower Room Humidity
The polyurethane will take longer to dry if the moisture content exceeds 50%. However, using a dehumidifier will lower the moisture content, and the polyurethane will dry faster.
Here’s how to use a dehumidifier to speed up the polyurethane drying time:
- Turn On The Dehumidifier – The dehumidifier will draw in air, condense (or remove) the moisture in the air, and release dry air into the atmosphere. This decreases the moisture content and helps the polyurethane dry faster.
- Keep The Dehumidifier Running – You can keep the dehumidifier running for hours. The longer the dehumidifier works, the lower the moisture content will be, and the faster polyurethane will dry.
Method 4: Allow Proper Room Ventilation
Before applying polyurethane, open all windows and doors to allow proper air circulation. If the air is circulating properly, the rate of evaporation and oxidization will increase. This speeds up the polyurethane drying and curing time.
Other tips that can help polyurethane dry faster are:
- Use water-based polyurethane because oil-based polyurethane takes longer to dry.
- Apply polyurethane early in the day before the weather gets hot.
- Turn on fans in the room while applying the polyurethane.
- Apply the polyurethane in proper painting conditions. Humidity should be less than 50%, and temperature should be between 50-80 degrees (F).
Polyurethane is Dry If:
To know if polyurethane is dry, inspect the texture of the finish. If the finish looks wet or tacky, the finish isn’t dry yet. If the polyurethane finish is shiny and reflective, the polyurethane is dry.
Another way to know if the polyurethane is dry is to use the nail test. Swipe your nail (or a razor) across the polyurethane coating; if polyurethane builds up in your nail, it hasn’t dried yet. If the polyurethane doesn’t build up or get removed, it has dried.
You can also use sandpaper to know if the polyurethane has dried. Swipe across the finish a fine-grit sandpaper. If the sandpaper clogs up, the polyurethane hasn’t dried. On the other hand, the polyurethane has dried if the sandpaper doesn’t clog up and goes smoothly over the surface.
Don’t Re-coat Too Soon
If you re-coat polyurethane too soon, the second or third coat will not stick well to the existing coating. This is because moisture (oil or water) will still be trapped in the polyurethane coating. The trapped moisture will repel the second coat. If that happens, the finish will be uneven, blurry, and tacky for several days.
When you re-coat polyurethane too soon, the existing coating won’t have enough time to dry and cure. This means evaporation and oxidization processes will be halted when you apply a new polyurethane coating.
Since evaporation and oxidization are stopped, moisture will be trapped in the polyurethane. The trapped moisture will prevent the second coat from adhering properly, and the entire finish will peel off.
Also, trapped moisture will bleed through. When a second coat is applied, it seals the existing coat. And, since polyurethane is water-resistant, the trapped moisture will have nowhere to go but bleed through the second coat. This will cause stains and uneven drying.
The finish will become semi-solid or tacky if you re-coat over a tinted polyurethane too soon.
Water-based and oil-based polyurethane have different drying times. Oil-based polyurethane takes 24 hours to dry for a re-coat, while water-based polyurethane takes 8 hours.
However, you can speed up polyurethane drying time by increasing the heat around the paint coating.