Choosing Between Use of Rock Salt vs Liquid Deicer is Not as Simple as 'One Size Fits All'

Over the past couple of years, more snow removal contractors have begun to experiment with liquid ice-melting products. By and large, liquid ice melters are being used in one of two ways: 1) as an anti-icer put down before a snowfall to pre-treat the surface or 2) after a snowfall as a pre-wetting agent where the liquid solution is sprayed onto rock salt as the salt is exiting the spreader.

Generally, while more expensive, use of liquids are considered to have an impact on cutting overall operations costs, increasing profits and improving sustainability.

Ultimately, the choice of using rock salt vs liquid deicer is not as simple as “one size fits all.”

“Rock salt and liquid deicers are both important tools in the winter maintenance toolbox and are used in different ways – sometimes alone and sometimes together, depending on the particular conditions,” says Scott Koefod, Ph.D., Principal Scientist, Cargill Road Safety.

It all depends on temperature.

Ken Rost, CEO of Frost inc., explains if you are trying to remove existing ice, salt can sit on ice and do nothing unless the temperature is 15-17 degrees Fahrenheit or higher. “In colder climates like the upper Midwest, liquid ice control products are more effective because of their ability to work effectively down to -25 F,” he says.

And so, the debate rages on.

There will always be a place for salt and there will always be contractors and contracts that will specify the use of traditional salt application methods.Cargill Road SafetySpreading it out

There will always be a place for salt and there will always be contractors and contracts that will specify the use of traditional salt application methods.

Koefod says using salt is far and away the most cost-effective ice melting chemical.

“Nothing else comes close,” he says. “Indeed, if the temperature is not too cold and with the help of the sun, at a pavement temperature of 30 degrees Fahrenheit, $1 worth of salt can melt over 1,500 lbs. of ice.”

Also, he says salt is readily available in quantities needed for deicing and it is relatively benign and safe.

“The benefits of deicing with salt have been well-documented,” he adds. “Studies have found that road salting and plowing can reduce traffic injury crashes by up to 88%, and the economic cost of snow related road closures can cost a state between $300 million and $700 million per day.”

The primary argument against use of sale as a deicer is the decline in ice melting action as the temperature drops. Koefod says other chemicals, such as magnesium chloride and calcium chloride, are faster ice melters (even as solids) and are effective to considerably lower temperatures than salt, though they are also significantly more expensive.

“Not everyone wants to pay for a higher level of service,” Rost says. “Unfortunately issues like bounce and scatter, and plowing off during multiple snow events, puts more salt into our environment. As higher salinity values are measured in our surface runoff water, we are going to see more pressure for regulation on salt usage. We might as well start thinking differently today.”

Another argument against salt is it being corrosive to steel. However, this is true of all the commonly used chloride salt deicers.

“Like all human activities, it has its own unique types of potential environmental impact that must be managed,” Koefod says. “Our industry is very active in education of our winter maintenance professionals to help them use best practices so that salt is used in an environmentally responsible and sustainable fashion.”

Reality vs fantasy

A common misconception by contractors considering using liquids is the idea that the liquids will replace use of salt completely and be a cure all for deicing.

Koefod points out that really, even solid deicers like rock salt are liquid deicers in operation.

The starting point with liquids is usually a sodium chloride brine, which is salt mixed with water. What is commonly seen in the market is products being added to that mixture such as magnesium chloride, calcium chloride or any of a variety of agricultural-based products in effort to reduce the freezing point of water and allow the brine to work at lower temperatures and get more pushes at a site.

“All chemical deicers work the same way, they lower the freezing point of water, and if they can lower the freezing point below the actual temperature of the ice, the ice melts,” Koefod says. “To do this, there must be physical contact between the chemical and the ice.”

When a solid crystal of rock salt contacts ice, he says only a miniscule amount of chemical is in actual contact with the ice, leaving most of the chemical “locked up” inside the salt crystal and never in touch with the ice.

It is only when the ice melting process begins and some melt forms that things begin to speed up.  Once a bit of ice has melted, it will dissolve more of the salt and form a brine.  Koefod says the brine, in turn, will start to spread out and allow the salt “molecules” to more efficiently contact the ice and melt it.  “Thus, for the most part, it is always a brine that is doing most of the actual ice melting work by permitting efficient contact between the chemical and the ice,” he says. “You can think of the solid salt as a kind of reservoir or ‘gas station’ that can continue to ‘pump’ more chemical into the ice melt brine, allowing it to continue its relatively rapid ice melting action.”

Not all liquid products are created equal in terms of temperatures ranges that they are effective at.

Generally, working temperature for basic brine is 18 degrees. The various additives help reduce that working temperature to below zero.

“Liquid ice control products like calcium chloride applied with a straight stream can burn through existing ice at any temperature to get down to the surface,” Rost says. “It then spreads under the ice interrupting the bond between ice and the surface and the ice can then be removed.”

Salt can do some of this too, but only at higher temps and the risk of refreeze is greater.

Is liquid deicer the answer?

Despite the similarities of general purpose, Rost maintains that liquid ice control products are more powerful than dry salt.

“It's important to know that liquid ice control products can be used as deicers, but they are more effective when they are pre-applied as an anti-icer,” he says. “When used as a pretreat anti-icer, less product is necessary to disrupt bonding between ice and the surface. I have always used the example of trying to fry an egg in a cast iron pan without oil versus with oil. If you pretreat the surface, you will prevent the bonding of snow and ice in the same way.”

Both Rost and Koefod agree that liquids are powerful ice melters.

“This allows contractors to get surfaces cleared much faster and this is what the customers want,” Rost says. “Because they are more powerful, less can be used to achieve a similar result and this has a positive benefit for the environment.”

Koefod points out that all ice melt chemicals are limited by two things: the available ice melting capacity (pounds of ice that can be melted per pound of chemical) and ice melting speed (how quickly a chemical can produce its ice melting capacity). Both markers decrease as the temperature drops below freezing.

Ice melting capacity cannot be changed, it is a characteristic constant of any chemical at a given temperature. As a result, Koefod says if it takes so many pounds of salt per square foot to provide sufficient ice melting capacity at 25 degrees Fahrenheit and the temperature drops to 15 degrees Fahrenheit, the only way to achieve the same amount of ice melting capacity is to apply more chemical.

As example, he says salt’s ice melting action becomes much slower as temperature drops. Koefod says it can take salt up to 2 days to generate all its available ice melting capacity at temperatures below 0 degrees Fahrenheit. Typically, contractors can’t wait that long for deicer to work.

Conversely, liquids do not have the same problem, being faster ice melters on their own, they also accelerate the ice melting action of rock salt.

“By blending rock salt with a liquid, in a practice known as pre-wetting, the wet salt will start working faster, especially at colder temperatures,” Koefod says.

Pre-wetting can be accomplished in a variety of ways. Some operators have equipment that allows them to spray a liquid on the salt as it is ejected from the spreader. It is also possible to treat the rock salt with liquid in advance or buy rock salt that has been pre-treated with a liquid for easy use.

By pre-wetting salt with a liquid, the salt sticks to the pavement better, so less salt is bouncing or scattering and also works faster to melt the snow and ice.Cargill Road Safety“By pre-wetting the salt with a liquid, the salt sticks to the pavement better, less salt is lost by bouncing or scattering and, as mentioned above, also works faster, with the net result being that pre-wetted salt can be applied at about 30% lower application rates than dry salt to achieve the same performance,” Koefod says.

Another benefit of liquids is a more efficient application of deicing chemical and overall reduced application rates, reducing costs.

One method is through anti-icing, through which the deicing chemical is applied to the pavement surface before the storm begins so that it can prevent snow from compacting and bonding to the surface as soon as it falls, facilitating its removal and helping keep that pavement safe until the plows arrive. 

“This is always the most efficient way to use ice melting chemicals, it takes only about 25% as much salt to prevent snow from bonding than to break the bond after it has formed.,” Koefod says. “Liquids are the ideal way to apply anti-icing chemical because they permit application of a small amount of chemical more uniformly than is possible with rock salt.”

Applying liquid deicer prior to a storm, prevents the snow from compacting and binding to the pavement, allowing for easier removal.Frost Inc.However, he explains that anti-icing cannot always be done and conventional, reactive deicing with rock salt is still needed, but liquids also help to improve the efficiency of rock salt deicing.

A drawback to using liquids is that they cannot be used during a rainstorm event preceding a snowstorm. Also, while they are very fast ice melters, they have a relatively low ice melting capacity, hence why liquids are traditionally used in that anti-icing capacity or pre-wetting of salt to help “activate” it more quickly.

Koefod says another potential con of liquids is that under certain circumstances they can cause slipperiness (particularly magnesium chloride or calcium chloride liquids) and so should be used with appropriate training and care.

Customer buy-in

Despite similarities in purpose, liquid ice control products are more powerful than dry salt.Frost Inc.Transitioning to use of liquids as part of a snow and ice management contract can be challenging to explain to clients. Many property owners or managers are averse to use of liquids and want the more common sight of salt on the ground as proof that the contractor was present.

It is important to educate your clients, while also maintaining the right to use the best tool for the job.

“A wide range of best practices in deicing have developed over the years and there are more tools and techniques available today than ever before to help winter maintenance professionals do their jobs more effectively and efficiently,” Koefod says.

Rost agrees, noting that knowing what liquid products will work in a specific climate takes a lot of education and a little bit of trial and error.  “Contractors that are willing to break from tradition and get out and pretreat prior to snow events will be more efficient and successful using liquids,” he says.

The potential increased revenue comes from demonstrating the added value of service and ability to clear surfaces faster and more thoroughly.

“Contractors that offer this service are the leaders in their markets and are going to be better suited to win premium contracts,” Rost says.