The Salt Mines in Northern Ireland extract up to half a million tonnes of rock salt grit every year for use on the roads all over Ireland and the UK and even as far as the USA. The Rock Salt Grit is more than 90% pure Sodium Chloride (salt) with the remaining insolubles being mostly Marl (mudstone or siltstone). This Marl helps improve traction under foot and between the wheels of vehicles and the highway. It is preferred by the Road Service for de-icing the public highways - over 2 million tonnes are spread on UK roads every year.
How Salt Works
Salt works by lowering the melting point of ice. When salt mixes with water or moisture, it creates a saline solution (salty water). In the same way as it needs to be really cold for seawater to freeze, this saline solution will freeze at a lower point than fresh water. The temperature at which it freezes will depend on the salinity of the water (how salty it is).
Does salt work on snow?
Salt will not directly melt snow. It needs to mix with water or moisture to create a saline solution which will in turn melt snow. The Road Service often tells us that the roads have been gritted but it takes cars to drive through the snow to mix up the salt and snow and moisture to help with the melting process.
Is it better to put salt or grit down before or after snow?
Scattering salt on top of snow will have a limited effect. There needs to be a salt saline mix on the ground for the snow to land on and in turn melt. The salt will reduce the chance of the snow freezing to the ground. If there are heavy falls of snow, the snow will simply lie on top of the snow. The snow will need to be cleared away (ploughed or pushed) and salt spread on the ground to reduce the build up of ice.
Can I keep my grit salt for next year?
Rock Salt has been forming in the ground for hundreds of millions of years. Of course it is best that it is kept somewhere dry so it does not dissolve but if it is stored properly, in its sealed bags preferably, then it should definitely keep for another year if it is not used this winter. There is an anti-caking agent added to the salt which works by preventing it from clumping together even it does get wet. If you are using a non-salt deicer such as exoTHAW, it should be kept inside somewhere dry as it absorbs and reacts with moisture and may become hard and unusable if not stored properly.
Both are relatively equally effective providing the salt content is the same. White is preferred by some as it cant be seen and doesn't stain the snow. The Rock Salt Grit is preferred for providing better traction under foot. exoTHAW Calcium Chloride deicer is much more expensive that other salt because it it mush fast acting (as it creates heat as it reacts with moisture) and works down to temperatures as low as -32oC
Is salt corrosive?
Salt (white salt or rock salt grit) has a corrosive effect on metals, tarmac and concrete. It also has a damaging effect on plants and is toxic in high enough levels for animals. Salt should be stored properly so that it does not get damp and cause a leakage into water courses and onto vegetation. Whilst all de-icers do have a negative effect on metals, tarmac and concrete, the best option is to use a non-salt de-icer such as exoTHAW.
Where does the salt come from?
Our brown Rock Salt Grit is mined at the Belfast Lough. Our white salt is usually European, Turkish or Egyptian marine salt although this may change from year to year.