Bitter Cold Temperatures & Rock Salt
In order for salt to effectively work, salt needs to dissolve and form a solution of salt and water, which is called brine. As temperatures drop to below -10 degrees, salt cannot form its own natural brine with existing snow readily. A sunny day will aid with the creation of brine at lower temperatures.
Treated Rock Salt
Treated rock salt is made available when temperatures remain constantly below -10 degrees. Rock salt is treated (or coated) with an activator to allow the salt to form brine at lower temperatures. Treated rock salt is best used on hills, entrances and icy surfaces. As the rock salt is 'treated' with an activator (such as beet juice), staining may occur on carpeted surfaces; therefore, the treated rock salt will not be used on doorway entrances.