With November winds and the approaching winter, a young man’s mind (well, not so young anymore) turns to snow and ice. Oh, and rock salt. In our decade in the salt biz, I’ve been frequently asked ‘how much salt should I put down?” and I began to do a little research to see if there really is a “magic number.” As a for-profit business owner you would think that I would advocate the over-application of rock salt but, hey, I do have some morals and ethics.
Rock salt admittedly has some environmental risk, but it becomes an unavoidable safety necessity during Michigan’s winter weather. When applied incorrectly salt can linger in the soil and eventually work its way into the groundwater. The best way to reduce our negative impact on the environment is to look for the “perfect” amount to apply that melts the ice without melting your wallet.
How does rock salt work? Technically, it doesn’t actually melt ice, but it prevents the cold water from forming ice crystals. As a mass of water approaches 32F, the molecules slow down and move closer together. At freezing, the molecules' electrical charges allow them to combine into ice crystals. Rock salt (Sodium Chloride) forms two particles, a positive sodium ion and a negative chloride ion. These ions occupy the space between the water molecules preventing them from latching on to each other and producing ice crystals.
Why the chemistry lesson? (Careful, there may be a pop quiz later.) Well, once enough sodium chloride is applied there comes a point that more is not better, faster, safer, or more effective. Many variables can affect the “magic number” calculation but here goes: The best research I found for straight halite rock salt application shows between 300# and 800# per two lane mile is the optimal rate for roadways to melt the ice without leaving ineffective residual salt. Let's take an average from the survey results and use 500# per two lane mile; two lane miles is equal to 63,360 square feet or 1.45 acres, so 500# would translate into 5.8 acres per ton. For the homeowner...if your driveway is 1200 sq ft you’d need about 9.5 lbs of rock salt evenly applied. (and Sr. Rosemary said I wasn’t paying attention in math). Intuitively, these numbers sound low; my personal experience has numbers closer to 2.33 acres per ton or 25 lbs for that driveway. Maybe I'm the over-applying type? or maybe those survey numbers are too conservative. I think we'll all find out this winter...
Rock salt admittedly has some environmental risk, but it becomes an unavoidable safety necessity during Michigan’s winter weather. When applied incorrectly salt can linger in the soil and eventually work its way into the groundwater. The best way to reduce our negative impact on the environment is to look for the “perfect” amount to apply that melts the ice without melting your wallet.
How does rock salt work? Technically, it doesn’t actually melt ice, but it prevents the cold water from forming ice crystals. As a mass of water approaches 32F, the molecules slow down and move closer together. At freezing, the molecules' electrical charges allow them to combine into ice crystals. Rock salt (Sodium Chloride) forms two particles, a positive sodium ion and a negative chloride ion. These ions occupy the space between the water molecules preventing them from latching on to each other and producing ice crystals.
Why the chemistry lesson? (Careful, there may be a pop quiz later.) Well, once enough sodium chloride is applied there comes a point that more is not better, faster, safer, or more effective. Many variables can affect the “magic number” calculation but here goes: The best research I found for straight halite rock salt application shows between 300# and 800# per two lane mile is the optimal rate for roadways to melt the ice without leaving ineffective residual salt. Let's take an average from the survey results and use 500# per two lane mile; two lane miles is equal to 63,360 square feet or 1.45 acres, so 500# would translate into 5.8 acres per ton. For the homeowner...if your driveway is 1200 sq ft you’d need about 9.5 lbs of rock salt evenly applied. (and Sr. Rosemary said I wasn’t paying attention in math). Intuitively, these numbers sound low; my personal experience has numbers closer to 2.33 acres per ton or 25 lbs for that driveway. Maybe I'm the over-applying type? or maybe those survey numbers are too conservative. I think we'll all find out this winter...
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