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The crystallization of deicing salts found in many snow and ice melters can cause severe deterioration of stone, terrazzo and masonry surfaces. This crystallization is called subflorescence. Snow and ice melters containing calcium chloride, etc., are the cause for this damage.

Problems associated with subflorescence can be diagnosed and identified by visual clues, such as spalling and pitting. Accurate diagnoses of subflorescence can be confirmed with laboratory testing. Preventive applications might include an application of chemical injection and coating the masonry with a sealer or impregnator as well as switching to a snow and ice melters that contain noncrystalline salts. The following article will explore the problems caused by these deicers and what can be done to prevent damage to your stone, terrazzo or masonry floors.

HOW DO DEICERS CAUSE DAMAGE?

The deposit of salts in the pores of stone and masonry is the major cause for deterioration of these surfaces, and these salts are contained in many popular snow and ice melters. When snow and ice melts, the salts used in deicers become soluble. The water wicks into the pores of the stone and masonry carrying the salts with it. When the water evaporates, the salts recrystallize. The pressure created in the pores of the stone and masonry cause the surface to flake off or spall. This process is known as subflorescence.

DIAGNOSING AND IDENTIFYING SUBFLORESCENCE

An experienced stone consultant can recognize the signs and symptoms of damage caused by deicing salts. The stone and masonry will appear pitted (spalled). This damage is observed in the walking path at the entrances of buildings. The damage tends to lessen the when going farther away from the entrance. Certain stones such as some limestone and slate will flake off in sheets. Terrazzo and marble will become pitted. Core samples can also be taken and sent to a lab for testing and verification if necessary.

SNOW AND ICE MELTERS

There are many brands of snow melters on the market. Many of these melters contain salts that will crystallize and cause damage to stone and masonry. The following are the salts you should avoid.

Rock salt — Rock salt will go by the name of Halite but chemically it is simply sodium chloride (NaCl). This is the most common salt sold for deicing, and it is also the least expensive and hence is the most widely used. It is also the salt that causes the most damage to stone, terrazzo and masonry flooring.

Calcium and magnesium chloride (CaCl₂, MgCl₂) — These are salts that come from natural salt deposits in the Great Salt Lake in Utah. They are also destructive to stone, terrazzo and masonry. They can deposit a film on the surface of the floor causing it to become slippery.

Potassium chloride (KCL) — This salt is not a very good deicer by itself and is often found mixed with other ingredients. It can be found sold as a safer salt for plants, but not for stone, terrazzo or masonry.

Ammonium sulphate ([NH₄]₂SO₄) — Stay far away from this salt. It is very damaging to stone, terrazzo and masonry. It's not used that much in deicers, but if you see it listed on the ingredients, don't buy it.