Polyurethane is one of the most popular wood finishes on the market. It’s easy to apply, and dries fast. Plus, it is one of the more durable wood sealers you can use to safeguard wood from water-damage.
But, a quick-drying finish can only dry as fast as conditions will allow. Too much humidity, and polyurethane will struggle to cure. Too much heat, and it can begin to bubble.
Related Post: Can You Avoid Dried Air Bubbles Appearing In Your Polyurethane Finish?
But what about when it comes to very cold weather? How do you get polyurethane to dry when the temperature drops?
Well, in this post you will learn exactly why polyurethane struggles to dry at below freezing temperatures. You will also find out polyurethanes ideal drying temperature range.
And keep reading to discover why even cool (but not freezing) temperatures can slow polyurethane down…
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What’s The Lowest Temperature You Can Apply Polyurethane?
Polyurethane sealers, after they’ve dried and cured, can endure temperatures as low as -80°F (-62°C ).
But just because it can survive extreme cold, does not mean polyurethane can be applied at those low temperatures as well.
You see, in order to solidify, polyurethane (especially water-based polyurethanes) need to go through a process of evaporation.
Evaporation turns the liquid sealer into a solid film. Polyurethane then cures into a durable solid seal through a chemical reactive process called oxidation.
But, if its too cold, evaporation simply doesn’t happen.
Why Won’t Polyurethane Dry Below Freezing Temperatures?
Well, the problem with applying polyurethane at cold temperatures is that the cold hampers polyurethanes evaporation process.
The water inside the water-based poly simply won’t evaporate below freezing. That’s because water evaporates between 32°F (0°C) to 212°F (100°C).
Of course the warmer things are, (at the upper end of the above temperature range), the faster water will evaporate.
Even at a little above freezing — around 41°F (5°C) — polyurethane can take over three times longer to dry. That’s compared to it drying in ideal conditions.
So What Happens When You Apply Polyurethane In Cold Weather?
Not very much…which is the problem.
At room temperature, quick-drying polyurethanes can take between 4-6 hours to dry. But, if the temperature is too cold, polyurethane will remain tacky to the touch.
That’s not to say it will never dry. Polyurethane will dry eventually, as long as that cool room’s temperature is above freezing.
Nonetheless, you’ll be waiting around for a while.
OK. And How Warm Does It Have To Be For Polyurethane To Dry?
In perfect conditions, polyurethane should be cooling its heels in a room with a temperature between 70°F (21°C) to 77°F (25°C).
And that temperature should be coupled with moderate humidity. Ideally, no less than 40% RH (Relative Humidity) and no higher than 70% RH.
Related Post: Can Applying Polyurethane Over Tacky Wood Stain Work Out?
So How Can I Make Polyurethane Dry Faster?
There are a few things you can do. But your next step mainly depends on what specifically is preventing that polyurethane from drying.
If cold temps are the problem, then simply turn up the heat. If humidity is stopping poly from curing, then switch on a nearby dehumidifier.
Or you can check out our post right here on The Woodwork Place: Polyurethane Not Drying? What You Can Do To Fix It
In that post, we guide you step-by-step through the five main causes that prevent polyurethane from drying. And then we give you tips on what you can do to fix it.
Plus, there’s also advice on what NOT to do to make polyurethane dry faster.
To Wrap Up, Here Are The 3 Key Takeaways From This Post…
- 1). Polyurethane dries the fastest in moderate humidity temperatures ranging 70°F (21°C) to 77°F (25°C).
- 2). Polyurethane, (especially water-based polyurethanes), cannot dry below freezing.
- 3). At temperatures of around 41°F (5°C), polyurethane can take over three times longer to dry.
Heintz, Amy M., et al. “Effects of reaction temperature on the formation of polyurethane prepolymer structures.” Macromolecules 36.8 (2003): 2695-2704.