Clearing your sidewalk and driveway can be a difficult task after a large snowfall. When shoveling doesn’t do the trick, a chemical deicing agent may be beneficial. De-icers come in many different forms and are made from many different chemicals. You can purchase de-icers as pellets, particles, flakes and liquids. Although many different chemicals can be used, the five most common are:

• Sodium Chloride: Often referred to as rock salt, this is one of the most inexpensive deicers;
• Calcium Chloride: Studies have shown that this chemical tends to work better than other deicing agents – especially at lower temperatures – because it gives off heat as it melts;
• Potassium Chloride: This is a naturally-occurring chemical that is also used as a fertilizer and food salt substitute;
• Calcium Magnesium Acetate (CMA): CMA is a salt-free melting agent made from limestone and acetic acids (the main compound of vinegar); and
• Urea: Made from ammonia and carbon dioxide, this chemical is also used as nitrogen-based fertilizer.

How De-Icers Work

Since many deicers are made from a variety of chemicals, it is important to follow manufacturer’s instructions. De-icers aren’t meant to melt every piece of ice; instead, they break the bond between ice and pavement, making it easier for you to mechanically or manually remove the remaining ice and snow.

De-icers can’t melt snow and ice in a dry solid state. They first must attract or come into contact with moisture to form a chemical/water solution called brine. The brine then penetrates down through the ice and snow until it reaches the pavement. Once it is on the pavement surface, it spreads outwards, melting and undercutting the ice and snow, readying it for plowing or shoveling.

Because there are so many different chemical de-icers on the market (made from a variety of ingredients), each de-icer works in a different way. Some chemicals take longer than others to penetrate the ice and snow. Studies have shown that calcium chloride and magnesium chloride have the greatest ability to attract and retain moisture from its surrounds, with calcium chloride melting more ice than any other de-icer.

Sodium chloride, on the other hand, is the most popular deicer. It’s inexpensive, effective, and easy to store and apply. It comes from rock salt that has been crushed, screened, and treated with an anti-caking agent.

When these de-icers are thrown on the road, it lowers the freezing temperature of water and prevents ice from forming on the ground. When cars and other vehicles drive over the salt crystals, their sheer weight applies force onto the ice, which pierces the snow and shatters the ice.

The Problem With Chemical De-Icers

Chemical de-icers have the potential to damage grass and other plants if their concentration in the soil becomes too high. Manufacturers can sometimes add dangerous chemicals to keep salts from clumping together. In high concentrations, the various ingredients can stunt or kill plants and pollute rivers and streams through storm runoff – which ultimately can harm birds and fish.

Magnesium chloride is one of the most popular choices; it can contain a derivative of cyanide. The high phosphorus content of some de-icers can contributes to algae blooms, which deprives water of oxygen needed by aquatic animals and plants.

According to the National Wildlife Federation, extensive use of potassium chloride has the potential of inducing plant damage through nutrient imbalances and excessive amounts of soluble salts. Soil, vegetation, and water (including the fish and aquatic plants that live in it) are also adversely affected. Most soil and vegetation damage occurs within 60 feet of the road and is greatest close to the pavement.

Only plant salt-tolerant vegetation near the road – they are more likely to survive and will help to absorb excess salt before it drains into local waterways. A few examples of salt-tolerant plants (although the ability to plant these depends on region) are:

• Blue spruce;
• Horse chestnut;
• Red cedar;
• Sumac;
• Willow;
• Black locust;
• Redbud;
• Hawthorn;
• Walnut; and
• Dogwood.

On a side note, there is minimal chance of damage to trees, grass, and shrubs in the minimal amounts recommended for driveway and sidewalk deicing. The de-icers used to salt roads and bridges, however, are a different story.

De-icers used to salt roads and bridges are much more highly concentrated so you should be sure to clean your car frequently during the winter. Salt de-icers can accelerate the corrosion of unprotected iron and steel by holding moisture against the exposed surfaces.

Chemical de-icers can also lead to the corrosion of metal and infrastructures (concrete and steel are the main make-ups in bridges). It has been estimated that the annual road salt cost for motor vehicle and infrastructural damage is between $3.5 and $7 billion.

Sources: The Salt Institute; Evanston Environmental Association; National Wildlife Federation