Dealing with icy sidewalks is a fact of life in northern climates where snow and winter conditions are common. There are many different ways to deal with ice, whether using one of many chemical compounds to melt it or using more environmentally friendly products to provide traction and prevent slippage.
How De-Icers Work
Ice melt products attract moisture to themselves to form a liquid brine which generates heat and melts ice. The product must reach the pavement to become effective. Once on the pavement, the brine can spread out and break the bond the ice has with the pavement. As the ice is loosened, it can more easily be shoveled away.
Every year there are more and more choices when it comes to de-icers. A lot of the choices are very similar and differ only in marketing with each product claiming to be the best. Typically blends are made to try and combine the best advantages of each chemical.
- Calcium chloride: This is the traditional ice melt. It will melt ice to temperatures of -25 degrees F. It gives off heat as it dissolves which melts the ice quicker but leaves a slimy residue. It is corrosive to metal and can be damaging to vegetation if over-applied. Magnesium chloride is a similar product and is becoming more popular. It is less corrosive and safer on concrete and plants.
- Sodium chloride: Also known as rock salt, this is the least expensive and very efficient. It will melt ice to temperatures of 20 degrees F and is effective at drying out icy surfaces. Rock salt is not as harmful to concrete as other products but can be damaging to vegetation and is corrosive to metal.
- Potassium chloride: A more expensive option than other products, it works well when mixed 50/50 with rock salt. Potassium chloride will melt ice to temperatures of 12 degrees F. It is relatively safe but can still cause plant injury if over-applied.
- Urea: Commonly used as a fertilizer, it is also an effective ice melter. It will melt ice to temperatures of 15 degrees F. Over application can harm vegetation.
- Calcium magnesium acetate (CMA): It is made from dolomitic limestone and acetic acid (the main compound in vinegar). It has little effect on plants and concrete, but its performance decreases at temperatures below 20 degrees F. It works differently than other materials in that it does not form a brine like salts. CMA helps prevent snow particles from sticking to each other on the road surface. It prevents re-freezing more than it melts ice and it tends to leave a slush.
Are They Harmful?
Given the alternative of dangerous conditions, the benefits can outweigh potential disadvantages. All de-icers have the potential to damage vegetation and concrete and corrode metal. Moderate use combined with adequate rainfall to dissolve and wash away product should be enough to protect vegetation and hard surfaces.
Damage to concrete occurs not from the effects of the salt but the effects of the freezing point of water. When the freezing point of water is lowered (by creating a brine), the number of freeze/thaw cycles increases and the expansion of freezing water (hydraulic pressure) can exceed the strengths of concrete.
Other, more natural, products can be used to treat icy sidewalks and driveways. Although they are less effective, they pose less harm to the environment and pets. Natural alternatives like sand, sawdust, wood shavings, and kitty litter are mainly effective for their gritty, anti-slip qualities. They provide better traction to walk on the ice but do not melt ice. They are often mixed with ice melt products as a way to use fewer chemicals.
There is a product called Magic Minus Zero which is a liquid de-icing agent made from a blend of magnesium chloride combined with an agricultural by-product of the distilling process. It is non-toxic, biodegradable and has a corrosion index lower than distilled water. Magic Minus Zero can be applied directly to paved surfaces in advance of a winter storm or can be sprayed onto regular rock salt.
- Do not over apply; follow instructions on the label.
- Do not try to melt everything. Clear snow first.
- Wear gloves. Ice melts are an irritant.
- Do not use on new concrete that has not fully cured.
- All products have some effect on the environment. Flush area with water if over-use is suspected or damage appears on plants.
Ice Melters and their Effect on Plants. North Carolina Cooperative Extension College of Agriculture and Life Sciences.
How Road Salt Harms the Environment. Columbia University Climate School.
Before You De-Ice With Urea. University of Maryland Extension.
Farnam, Yaghoob et al. The Influence of Calcium Chloride Deicing Salt on Phase Changes and Damage Development in Cementitious Materials. Cement & concrete composites vol. 64 (2015): 1-15. doi:10.1016/j.cemconcomp.2015.09.006