For any winter maintenance contractor, understanding how salt works to reduce the risk of ice is of the utmost importance.
Predicting road surface conditions from weather forecasts alone is not accurate enough to give a picture of what the current road temperatures are and what is happening on the surface of the road. Road surface temperatures tend to be a lot lower than air temperature and are effected by the moisture on the road.
Porous roads surfaces also chill a lot quicker than imperious surfaces and are a lot slower to warm up again. Porous surfaces tend to also waste smaller grit particles as they fall in-between the asphalt and are deemed useless.
Getting the correct application rate is also vitally important. Too little salt and the freezing point will not be raised enough to be effected, too much and excess salt is washed off the surface and makes its way to our rivers and watercourses causing environmental issues.
As a general rule, 10% salt solution freezes at -6°c, 20% salt solution freezes at -16°c, however if the road temperature falls below -9°c then salt will be inactive and sometimes the best solution is to spread sand for its gripping properties.
As a guideline to quantities, on imperious surfaces the quantities of rock salt that are required to be spread are as follows:
| Frost/ice/dry conditions | 10 – 15g per metre square |
| Frost/ice/wet conditions | 20 – 40g per metre square |
| Snow | 20 – 40g per metre square |
On porous surfaces the quantities generally need to be doubled.
It is important that we get the correct quantities of salt down onto the correct surface at the correct time to ensure an ice-free surface.