In any climate where temperatures reach below freezing, deicing walkways will be required for safety reasons. Yet all deicing methods are not created equal. The best available method is mechanical heating of the walkway surface to eliminate the chance for ice to form; however, this method is cost-prohibitive and not always practical to install for historic buildings. Alternative chemical deicers are more affordable, but come with a host of other considerations, including their compatibility with historic building materials.
The most common deicer used in the United States and internationally is sodium chloride (NaCl, or table salt). Sodium chloride is inexpensive and easily sourced, but employing it as a deicer can be very harmful to historic building fabric. Both sodium chloride and other salt-based deicers—including calcium chloride (CaCl2), magnesium chloride (MgCl2), and potassium chloride (KCl)—are highly corrosive to many building materials. So though sodium chloride is cost-effective, using it or other chlorides as deicers near a historic structure will necessitate more money and effort spent in conservation repairs over time.
Instead, building stewards should consider acetate deicers, the gentlest of which is calcium magnesium acetate (CMA). Sodium acetate (NaOAc) is also minimally corrosive. A third acetate deicer, potassium acetate (CH3COOK), is more corrosive but still less harmful than chloride deicers. By choosing one of these deicers instead of sodium chloride, time,money, and historic integrity can ultimately be saved.
