A guide to the use of chemicals for Ice and Snow control around buildings

A guide to the use of chemicals for Ice and Snow control around buildings

By James White MaintechMRO.com

Why use chemicals at all?

The removal of ice and snow by mechanical means is made more difficult by a layer of ice that bonds to substrates. After a fall of snow or the freezing of surface water by temperatures below freezing, ice will bond to concrete asphalt and other substrates. The addition of salt and other chemicals acts to lower the freezing point of water creating brine that will break the bond between the ice layer and the substrate making it easier to remove by mechanical means.

There are two types of chemical deicers. The first being endothermic, those that take heat from their surroundings to work such as rock salt (sodium chloride) which work best at temperatures around freezing and will only work down to a temperature of -6 to -9C. The second type is exothermic, these create heat when added ice and snow, such as Calcium Chloride and work down to a temperature of -28 to -30C.

Exothermic deicers tend to work faster than endothermic because they generate heat rather than need heat to work. Endothermic deicers take their heat from available sunshine, heat from the substrate e.g. pavement, and heat from the surrounding air. Endothermic deicer will also use friction as a source of heat and this is why rock salt can work successfully on roads in moderately low temperatures.

All chemical deicers work best if deployed in advance of ice forming, it is no-good putting a chemical deicer on 30cm of snow and expecting it the melt all the snow.

It is better to use too little rather than too much deicer. Too much rock salt will result in the brine turning back to crystal form having no greater effect. Too much calcium chloride which is hygroscopic, drawing moisture from its surroundings, will result in a greasy and slippery residue.

When deployed before the formation of ice, deicers can be used at a rate of 25-50g/m whereas more than 20 times this amount will be needed to completely melt 10cm of ice on 1m at temperatures of -5C. It is never recommended to use deicers in these high quantities, in a situation of thick snow or ice, use 100-250g/ m, the brine that is produced will help break the bond between ice and substrate allowing faster removal by mechanical means.

If the deicer cannot be deployed in advance of ice or snowfall, use as soon as possible i.e. as soon as the snow starts falling, to minimize the amount needed.

Detrimental effects of using chemical deicers

Concrete and Asphalt

There is still some debate about whether the salts damage concrete. There is general agreement that chemical deicer should not be used on concrete less than one year old and that any cracks are sealed and chips repaired in concrete before the onset of winter.

The main cause of damage to substrates such as concrete and asphalt are due to increased freeze thaw cycles when deicers are used. Water gets into cracks and porous parts of concrete and asphalt and expands when it freezes causing the breakdown of the substrate. This is very noticeable on road surfaces where rock salt has been used and the night time temperature dips below -6C. The water melts during daylight hours and freezes again at night damaging the road surface where it has penetrated causing potholes.

The use of Calcium Chloride which will not freeze above -28C will help prevent this type of damage.

Vegetation

Most damage appears to be caused where chemicals are applied in large quantities and traffic splashes brine or water runs off into gardens and lawns. Rock salt tends to cause more damage to vegetation than calcium chloride, however excessive use of any deicer will be detrimental to vegetation.

Metals

Chemical deicers will case corrosion to metal parts of building, fences and railings, this can be reduced by good maintenance practices including washing down and the use of protective coatings. Care should be taken when storing De-icing chemicals near metal objects.

Tracking inside

Rock salt will leave a white powdery residue that is unsightly and can damage carpets and floor finishes. Calcium chloride can leave an oily residue that can damage wax or urethane finishes on wood floors.

To prevent tracking do not over use deicers, clear the area nearest to entrances regularly and use track mats inside entrances.

Any tracked rock salt can be removed by vacuum cleaner or mop and calcium chloride using a mop with a good detergent.

Other types of chemical deicer

Potassium Chloride and Urea (endothermic)

These are common fertilizers but in high concentrations are deadly for plants. Work down to about -10C. Both materials work more slowly that calcium chloride

Magnesium Chloride (exothermic)

Benefits similar to calcium chloride, main draw back; it is only 48 percent active and therefore needs to be applied at a higher rate than calcium chloride.

Sodium Acetate & CMA

A dry formulation that is used on bridges, multi storey car parks and airport runways where reinforcing bars may be near the surface and it is not recommended to use chlorides. Sodium Acetate is also biodegradable, creating no problems in run off water. Sodium acetate & CMA work down to approximately -17C and melt rapidly similar to calcium chloride. Sodium Acetate & CMA are expensive. CMA is often used as a corrosion inhibitor and can be blended with rock salt and other deicing chemicals.

Potassium Acetate

A clear liquid that contains no chlorides. It is safer to use on structural steel and reinforced concrete. Can be corrosive and is often mixed with a corrosion inhibitor. Effective down to approximately -27C.

Alpha methyl glucoside (MG-104)

A corn by-product that is usually combined with other ingredients. MG-104 provides a catalytic effect that speeds melting, helps other chemicals to work at lower temperatures, and assists in the extension of the freeze-thaw cycles to reduce surface damage.

What to consider

Maintaining a safe environment, preventing slips and falls and keeping roads clear for access of people and materials are the priorities of maintenance and facilities managers in ice and snow conditions. An effective and fast acting deicer makes the removal of ice and snow easier thus saving time and money.

Facility and maintenance managers tend to rate qualities of a deicer in the following order.

Works fast

Doesn't harm concrete

Works at low temperatures

Prevents damage by extension of freeze thaw cycle

Non tracking

Safe for vegetation

Labour is always the biggest cost of ice and snow clearance so effectiveness has to be a major consideration. Conditions such as temperatures must be taken into account, temperatures around freezing and rock salt will be effective. Lower temperatures may call for calcium chloride for its effectiveness and extension of the freeze thaw cycle that will help prevent ongoing maintenance to substrates after the thaw.

Number one consideration, deploy deicer before snow and ice where possible.

References:

Chemicals for Snow and Ice Control Around Buildings - G.P. Williams

Ice melts dos and don'ts - Becky Mollenkamp

Maximizing Melters - Cathy Walker

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