Winter is a dangerous time for exposed concrete. Freeze-and-thaw cycles can cause bases to expand and heave, leaving cracks and uneven surfaces. But there’s another danger that’s often overlooked, especially by homeowners and businesses that are more concerned with convenience than safe ways to remove ice from walks, steps and driveways without causing damage—salt.

Sodium chloride is the same chemical as ordinary table salt. It’s inexpensive, so it’s the main ingredient in cheaper deicing products. While it will melt ice effectively down to about 10° F, it will damage concrete, metals, soil and plants if not used carefully.

Concrete is very alkaline and needs to stay that way to remain strong. It is also porous. Since dissolved salts are acidic, when they work their way into the concrete, they lower its alkalinity, thereby weakening it. The most common result is spalling—the pitting and flaking of the concrete surface. But over time, it also penetrates deeper, weakening the entire slab and encouraging cracks to form.

Moisture accelerates the penetration of salts into the concrete, so melting snow and ice add to the problem. One way to remove surface salts is to brush them away once the concrete is dry, but enough remains behind to do damage over time. Washing it away might remove more from the surface, but it comes with other hazards to surrounding plants and vegetation, as well as to the environment when it passes through the sewer system or groundwater.

Other salt-based deicing products include chlorides of calcium, potassium, and magnesium. Calcium chloride is widely used, and while it is less hazardous to vegetation than sodium chloride, as it melts ice it causes the surface to become slippery, presenting a hazard itself. Calcium chloride is popular as a deicer, though, because it’s relatively inexpensive and effective to about -15° F. But it’s still no friend of concrete and can damage the roots of plants if it reaches them. Potassium chloride can also cause severe damage to plants if splashed on foliage or allowed to soak into the soil and will damage concrete like sodium and calcium compounds.

Magnesium chloride in the form of calcium magnesium acetate (CMA) has come into widespread use as a safer deicer by road and highway crews. It’s made from limestone and acetic acid (the main ingredient in vinegar) and works differently from other salts in that it prevents snowflakes from sticking to each other. While it has little effect on concrete and vegetation, it’s less commonly available to consumers, is more expensive, and works best at temperatures above +20° F, limiting its effectiveness in many icing situations.

While all of these products can be acceptable if used carefully, the best advice is to prevent ice buildup by removing snow before it can be compacted by foot traffic or vehicles or partially thaw and refreeze.

As a concrete professional, you might want to share this information with your customers to help them maintain their concrete surfaces properly. It’s good customer relations and might even prevent them from blaming you if problems pop up from ignoring your advice.

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