The question of whether chemical products used to clear walkways—often generically called “salt”—work on snow as well as ice is common. The answer lies in the fundamental difference between the two forms of frozen water. Snow is characterized by its light, airy structure and low density, while ice is a dense, compacted layer of frozen water. Understanding this distinction is key to effectively using de-icing chemicals.
How Ice Melt Works
All chemical de-icers function by exploiting a scientific principle known as Freezing Point Depression (FPD). Water normally freezes at 32°F (0°C), but when a solute, such as a salt compound, is dissolved into it, the freezing point of the resulting solution is lowered. This effect is a colligative property, meaning the reduction in temperature is dependent on the number of dissolved particles, not their specific chemical identity.
When a granule of ice melt lands on a frozen surface, it must first dissolve in the thin layer of liquid water present on the surface. The dissolving chemical then dissociates into ions, which interfere with the ability of water molecules to align and form the rigid crystalline structure of ice. This interruption forces the water to require a much colder temperature to solidify.
The process of the solid chemical dissolving creates a liquid solution called brine, which has a lower freezing point than pure water. This brine penetrates the ice or snow, continuing to melt the frozen material by lowering its freezing temperature. The ability of the chemical to quickly form this concentrated brine solution determines its speed and efficiency in melting the surface.
Effectiveness on Snow Versus Ice
While chemical ice melt can technically melt snow, applying it to a bulk accumulation is highly inefficient and wasteful. The products are designed to break the bond between a compacted layer of ice and the underlying surface, not to clear large volumes of snow.
Snow’s structure is mostly air, meaning the chemical granules must penetrate a vast volume of low-density material before they can dissolve and create the necessary brine solution. A granule of ice melt that lands on thick snow is isolated, and its melting effect is localized and quickly diluted. This results in the chemical being spent on a small pocket of snow rather than contributing to widespread melting.
The products are most effective when applied to a thin layer of ice or a small remaining layer of snow after major clearing. When applied to compacted ice, the chemical dissolves quickly into the dense frozen water, immediately creating a potent brine. This brine tunnels through the ice and breaks its bond with the pavement.
Comparing Different Ice Melt Compounds
The term “ice melt” covers several different chemical compounds, and their effectiveness varies significantly based on temperature. Sodium chloride, commonly known as rock salt, is the most affordable option, but it loses its effectiveness dramatically below about 15°F to 20°F. This is because it is an endothermic chemical, meaning it must draw heat from its surroundings to dissolve and create the necessary melting solution.
Calcium chloride is a more powerful de-icer, capable of working in temperatures as low as -25°F. Unlike rock salt, calcium chloride is exothermic, meaning it releases heat when it dissolves. This accelerates the melting process and allows it to perform better in extreme cold.
Magnesium chloride offers a balance, remaining effective down to a range of -13°F to 5°F. It is generally considered less corrosive to concrete and vegetation than rock salt.
Other compounds like potassium chloride and urea are also used, but their effective working temperatures are often warmer, typically stopping around 12°F to 25°F. Users must consider the specific chemical’s temperature threshold and potential side effects, such as corrosiveness to concrete and metal or harm to nearby plants and pets.