Standard Tar Products in the New York Times

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Easing Removal Of Ice
JAY ROMANO
ANYONE who has been to a hardware store in winter knows that there are scores of products on the market designed to make ice- and snow-removal less of a backbreaking chore. But sorting through the various chemicals, compounds, combinations, concentrations and price-per-ice-melting-pound computations is better suited to a chemist with a degree in economics than to a homeowner with an inch of ice on his driveway.

"Not all de-icers are created equal," said Edward Chouinard, president of Standard Tar Products, a company based in Milwaukee that makes Snomelt Instant Ice Melter. "But virtually all de-icers work on the same basic principle: They lower the freezing point of the water produced by the ice they melt."

Mr. Chouinard, whose company manufactures de-icing products used by homeowners, commercial property managers and state and local highway departments, explained that while plain water freezes at 32 degrees Fahrenheit, the freezing point of water containing a de-icing chemical is lower than that — sometimes much lower.

"The nice thing about Snomelt is that it's exothermic," Mr. Chouinard said. "That means that when you mix it with water, it creates heat."

Some de-icers — for example, sodium chloride, better known as halite or rock salt — are endothermic, meaning that they need to absorb heat from the atmosphere, sunlight or friction from tires to melt ice or snow. As a result, while rock salt is the least expensive de-icing agent available — selling for anywhere from $2.50 to $4 for a 50-pound bag — it is only effective at temperatures above 15 or 20 degrees Fahrenheit.

Products like Snomelt, on the other hand, which is 90 to 95 percent calcium chloride and sells for about $15 for a 50-pound bag, can melt ice or snow at temperatures as low as minus 59 degrees Fahrenheit, depending on the concentration of the chemical in the solution produced by the melting ice — a solution that de-icing experts call "brine."

In fact, it is the brine produced by a de-icing product — rather than the melting action of the product itself — that does the work the homeowner is hoping to avoid.

Rick May, marketing manager for Dow Chemical in Midland, Mich., said that most de-icing products work by penetrating the ice, dissolving into brine and then seeping into the pores of the concrete under the ice. Once there, the brine breaks the bond between the ice and the sidewalk, making it easier to remove the ice.

Mr. May added that while calcium chloride can indeed melt ice at minus 59 degrees Farenheit, that is the "laboratory limit" of the chemical's effectiveness. "In the real world, its practical effective temperature is more like minus 28 degrees Fahrenheit," he said, adding that the effective temperature of the chemical decreases because its concentration in the brine becomes lower as more and more ice melts.

He also explained that since calcium chloride is effective at such a low temperature, products containing it are less likely to cause problems on concrete surfaces, which are vulnerable to damage as a result of being exposed to freeze-thaw cycles.

The damage occurs, he said, when water that has been melted by the de-icer refreezes because the temperature has dropped below the level at which the de-icer is effective. When that happens, the concrete may crack.

When de-icers like plain rock salt are used, Mr. May said, the freezing point of the brine is relatively high — around 15 to 20 degrees Fahrenheit — thereby making it more likely that the temperature will drop to a point where the melted ice will refreeze. When a de-icer like calcium chloride is used, on the other hand, the temperature would have to fall below minus 28 degrees for the ice to refreeze.

"De-icer damage to concrete is usually not a chemical reaction," Mr. May said. In addition to products like calcium chloride and sodium chloride — the most and least expensive consumer de-icing chemicals, respectively — other de-icers on the market include potassium chloride, magnesium chloride and urea, as well as various combinations of some or all of them.