Here's why:
* Rock salt (sodium chloride) is primarily composed of sodium chloride, which is a very effective de-icer. It lowers the freezing point of water, preventing ice from forming or melting existing ice.
* Sea salt contains a mixture of salts, including sodium chloride, magnesium chloride, and potassium chloride. While some of these salts also have de-icing properties, the presence of other minerals can reduce its overall effectiveness compared to pure sodium chloride.
* Sea salt is also more likely to leave behind a residue that can damage concrete and other surfaces.
Therefore, rock salt is the preferred choice for de-icing due to its higher concentration of sodium chloride and its lower cost.
