Rock salt is spread over the road or pavement and as vehicles or pedestrians move over it, the crystals are crushed and spread across the ice. The salt reacts with the water molecules, and the freezing point of the water falls.
A mixture of grit and rock salt is generally used to treat carriageways - the sandy grit does not melt the ice or snow directly, but it makes for a less slippery surface while the salt gets to work.
It's important to note that grit does not work if the temperature is too low - somewhere between -8 and -10 Celsius is its limit. Colder than this and salt water will still largely freeze.
How much grit should I use?
This will vary depending on the severity of the winter, and whether you're gritting proactively or reactively.
Cumbria County Council are experts in winter highway maintenance, with a vast area to treat and plenty of cold weather in and around the Lakes. Their website has an excellent winter roads section (found here: http://www.cumbria.gov.uk/snow/grittingfaqs.asp) and they say:
"To prevent ice from forming, we spread salt at 10-15 grammes per square metre. But more is needed to melt ice which has already formed and the rate of spread is increased to 20-40 grammes per square metre to achieve this."
So on a cold, clear day with a crisp night forecast, a light dusting of grit/salt mixture can save you having to spread up to four times as much the next morning.
Do I have to grit my premises?
Yes! To quote the Health & Safety Executive:
"Employers have to ensure that their employees and anyone else who could be affected by their work (such as visitors, members of the public, patients etc) are kept safe from harm and that their health is not affected.
This means slips and trips risks must be controlled to ensure people do not slip trip and fall."
I've heard that if I grit the pavement outside my property, I could be sued if someone falls - is this true?
The above article from a national newspaper quotes the President of the Association of Personal Injury Lawyers:
"This is a common misconception. By clearing the snow from your paths, you do not invite any extra liability that wouldn't have existed had you done nothing and left the snow on the ground. The only circumstance in which you might invite a claim was if you acted completely unreasonably, and somehow created a new latent hazard that had not existed before your actions."
The Guardian reporter goes on to add, however:
"For example, if you poured huge quantities of water on to your drive which then froze to create a dangerous hazard, that in theory might open you up to a claim, he suggests."
Spreading Icemelt™ on the pavement outside your building, or clearing a path through the snow with one of our Shovels, is good samaritan behaviour. If we all did our part this winter, Britain's pavements would be a safer place.