What Works at Coldest Temperatures?
Calcium chloride can be effective in cold-weather conditions down to minus 25 degrees Fahrenheit. In comparison, rock salt is effective down to 22 degrees Fahrenheit. Urea is effective to 15 degrees Fahrenheit and potassium chloride effective to 12 degrees Fahrenheit. Sodium Acetate and Calcium Magnesium Acetate are effective to 5 degrees Fahrenheit.
Recent reports from highway departments indicate the calcium chloride and sodium acetate can shield against frost and ice formation for several days following application. A highway superintendent described it as an almost shield-like effect.
The first measure of an ice melter's effectiveness is the range of temperatures in which it can provide deicing action (in a reasonable time period). The "practical" lowest temperature limits for these materials is defined as effective within 15-20 minutes of application and is listed next to the material. When reviewing deicing materials on the basis of their effectiveness at practical temperatures, they rank as follows:
"Scientifically proven to melt at temperatures to -5 degrees". This may be true, but this is a laboratory measurement taken in a controlled environment, not a practical ice melting temperature. In a laboratory, a liquid with a 10% concentration of salt will freeze at 20 degrees, a 20% solution will freeze at 2 degrees, a 23% solution will freeze at -5 degrees, and a 26% solution will freeze at -28 degrees. It's not likely that you will create an exact 23 percent concentration of salt out on the sidewalks.
The practical ice melting temperature is one at which visible ice melting occurs within 15 minutes of application. Temperatures given previously were the practical melting temperatures.