Q–Ice and snow cause big problems where I live. My sidewalks, driveway and concrete and wood steps get slippery. Is it safe to use deicing salts on concrete, asphalt and wood surfaces? I have been told that deicing salts can cause severe damage to concrete. Are there safer salts that work differently than others?
A–The damage to concrete most people fear is actually caused by the freezing and thawing of water that soaks into the upper surface of the concrete. The use of deicing salts increases the frequency of freeze-thaw cycles that a concrete sidewalk or driveway experiences. The volume of water increases by 9 percent when it freezes. This expansion creates internal pressures that can blast apart weak concrete.
Concrete that contains small air bubbles (air-entrained), a minimum of 564 pounds of cement per cubic yard (a six-bag mix) and a minimum amount of water when mixed (4-inch slump) can resist repeated episodes of ice expansion within the concrete.
In addition, the concrete must be moist cured at or above 50 degrees Fahrenheit for a minimum of seven days, produce a 28-day strength of 4,000 pounds per square inch and have a minimum drying time of 30 days before it is subjected to the first freeze-thaw cycle. These practices are commonly followed by experienced, professional concrete masons.
Deicing salts rarely cause problems on wood surfaces and asphalt. What little damage they may cause is far outweighed by the benefits of preventing personal injury as a result of a fall on some ice.
There are three primary deicing salts. Each has different characteristics. The most common deicing salt is regular rock salt or sodium chloride. It is widely available and can melt snow and ice until the temperature drops to between 16 and 20 F. Below these temperatures, the rock salt stops melting snow and ice. Rock salt also releases the highest amount of chloride ions when it dissolves. Chloride can pollute streams, rivers and lakes. The chloride also causes metal to corrode.
Calcium chloride is another deicing salt. Many people have seen these small rounded white pellets, which can continue to melt snow and ice as temperatures fall well below 0 F. This type of salt can cause skin irritation if your hands are moist when using it. Concentrations of calcium chloride can chemically attack concrete.
The newest deicing salt is magnesium chloride. It continues to melt snow and ice until the temperature reaches -13 F. This salt releases about 40 percent less chlorides into the environment than either rock salt or calcium chloride. It is also less damaging to concrete surfaces of questionable or unknown quality. Magnesium chloride is also less toxic to plants, trees and shrubs. It also does not leave a powder residue when tracked into your home.
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Have questions about the remodeling process? Write to Tim Carter, c/o The Chicago Tribune, P.O. Box 36352, Cincinnati, Ohio 45236-0352.
For a list of sources of magnesium chloride, test data of different salts and a list of 10 guidelines for proper concrete installation, send $3 and your name and address to Tim Carter at the above address. Ask for Builder Bulletin No. 246.
