When the winter ice rolls around making your driveway and path slippery it can be difficult to know exactly how much salt you should add to melt the ice.
Too little and it won't get the job done (or it'll take too long), too much as it's a waste of money and can cause damage to your plants, pets and even your concrete.
The ratio of salt to water or ice ultimately depends on what you're using it for.
If you're trying to thaw your driveway in the winter, you likely need less salt than you think. When distributed evenly, a single 12oz cup of road salt is sufficient for thawing a 20-foot driveway (approximately 500 square feet).
The colder the outside temperatures are the more salt you may need to apply or the longer you'll need to wait for the ice to full melt.
Using too much salt to de-ice your driveway and walkways can impact the local environment, your pets, and the integrity of your property. Too much salt or other ice melts can also be damaging to concrete, so you really only want to use the smallest amount possible to get the job done.
What Temperature Does Salt Stop Working To Melt Ice?
There's a common belief that most salt will stop working to melt ice below 16ºF (-9ºC), thanks to freezing point depression.
In reality, the salt will still work away at the ice, but it becomes significantly less effective.
At 30ºF (-1ºC), one pound of salt can melt 46.3 lbs of ice in five minutes. At 15ºF (-9ºC), it takes 60 minutes for one pound of salt to melt 6.3 lbs of ice. The efficacy continues to decrease in correlation with the temperature.
|Pavement Temperature (°F/ºC)||Amount of Ice Melted by 1 lb (0.45kgs) of NaCl||Melt Times|
|30ºF / -1ºC||46.3 lbs / 21 kgs||5 minutes|
|25ºF / -4ºC||14.4 lbs / 6.5 kgs||10 minutes|
|20ºF / -7ºC||8.6 lbs / 3.9 kgs||20 minutes|
|15ºF / -9ºC||6.3 lbs / 2.9 kgs||60 minutes|
|10ºF / -12ºC||4.9 lbs / 2.2 kgs||N/A|
|5ºF / -15ºC||4.1 lbs / 1.9 kgs||N/A|
|0ºF / -18ºC||3.7 lbs / 1.7 kgs||N/A|
|-6ºF / -21ºC||3.2 lbs / 1.45 kgs||N/A|
However, Sodium chloride isn't the only type of salt. Many ice melt products use other forms of salt to get the job done in extreme temperatures.
Magnesium chloride is estimated to work at temperatures as low as -15ºF (-30ºC), and Calcium chloride should work until -25ºF (-32ºC).
What Happens If You Put Salt On Ice?
Even though you can't see it, ice has a thin layer of water on top of it. When you apply salt, it prevents this water from freezing and starts to break down the underlying layers.
Without salt, the layer of water may get deeper (and visible) if the temperature warms slightly. If you live in a cold area, you've likely seen this in action.
There's ice on a sidewalk from a winter storm. The sun comes out and partially melts the ice, creating a visible layer of water over top. Then, the sun goes down and the ice refreezes into a thicker, smoother sheet.
If you're Canadian, it's basically what the Zamboni does with hot water.
When you add salt, it prevents that thin layer from refreezing. Then, it starts melting the layers of ice below, progressively until it's thawed.
Yet, there are a few disruptors to keep in mind when considering this process.
If the temperature drops below the freezing point of saltwater (16ºF or -9ºC), the salt becomes less effective. That's why people say road salt is ineffective in extreme cold.
Additionally, even though the salt is melting the ice, the remaining ice and slush surrounding it will be colder for a while as the salt “steals” the heat. Here are the 3 ways salt makes ice colder.
How Much Salt Should You Add To Your Cooler?
In the summertime salt can be added to the ice in your cooler to make the ice colder. This can help you keep items frozen and fresh for longer. But how much salt do you need to add to your cooler?
If you're adding salt to your cooler to keep contents cold, there's no perfect ratio, as there are many variables to consider.
Coolers work best with a 2:1 ratio of ice to contents. If you don't meet that ratio and have insufficient ice, salt is unlikely to have a strong effect.
Many adventurers find success by adding a few handfuls of table salt to their coolers. Others report adding half a box of rock salt to a cooler with positive results.
If you need a scientific approach, consider the salt ratio of seawater, which is typically around 35 grams (0.128 cups). So, adding about 1/4 cup of salt for each frozen liter of water is a good starting point.
Alternatively, creating reusable saltwater freezer packs or purchasing high-quality reusable freezer packs (like the Yeti brand) is an effective way to keep your cooler cold while minimizing the environmental impact.