Rock salt has long been a go-to item for clearing driveways and walkways of ice during the winter. But can de-icing salt be dangerous? When it comes to your concrete and asphalt surfaces, yes.
How de-icing salt works
When salt comes into contact with water, it lowers the freezing point—the temperature at which water freezes. Normally, the freezing point for water is 32 degrees Fahrenheit. As salt is added, a lower temperature is needed for freezing to occur. When roads, driveways and walkways are between 15 and 32 degrees Fahrenheit, placing rock salt on top of the ice can dissolve the ice and turn it into liquid water. But below 15 degrees, salt cannot penetrate the ice well enough to dissolve it.
The effect of rock salt on concrete
Although concrete is a solid material, sturdy enough for walking on and building with, it’s also incredibly porous.
Concrete absorbs water like a sponge, including ice melted by rock salt. Since salt is hydroscopic, it actually pulls extra water into the concrete — about 10 percent more than water without salt.
Because temperatures fluctuate during the winter, there is a strong chance that the concrete will dip below 15 degrees, which means that the water will freeze again. Ice then expands and exerts pressure on the concrete that will crack it and cause flaking. The newer the concrete is, the greater the damage will be.
The effect of rock salt on asphalt
Asphalt is not as porous as concrete, making it less susceptible to damage from rock salt. However, older asphalt surfaces that have already been cracked or damaged provide easy avenues for the salt-infused water to get inside. Once it does, asphalt, like concrete, is damaged by the expansion of water as it freezes. If you have an asphalt surface that is more than a few years old or has sustained visible damage, avoid using rock salt.
Alternatives to de-icing salt
Calcium chloride is a good alternative to rock salt if you are looking to melt ice, not just add traction; this chemical compound will melt ice at temperatures as low as -25 degrees Fahrenheit. Other effective alternatives include sand, coffee grinds and cat litter.
No matter what option you choose, it is vital that you manage any ice on your property to prevent liabilities. Speak with your insurance broker about the liability coverage built into your homeowner’s insurance.
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