Nov
9
2015

Rock Salt – Spreading Guide

gritting

With the UK’s unpredictable weather, you can never be too prepared for a sudden drop in temperatures!

Rock salt is the most common form of ‘grit’ and is widely used across the UK to treat roads and pathways  to prevent frost forming on the surface.

Here is our quick guide to what rock salt is, when it should be spread and how much should be used.

Why rock salt and grit?

The main reason rock salt is effective is because it has a lower freezing point than water. By spreading rock salt onto a road, path or driveway, when vehicles or pedestrians manoeuvre over it, the crystals crush and spread across the ice. This causes a reaction between the water molecules and rock salt which prevents ice developing.

However, it is important to know that rock salt has a limit. On average, rock salt will have minimal effect on temperatures below -5 and will have virtually no effect on temperatures below -10.

There are two types of rock salt – brown and white.

The benefits of brown rock salt are that it is a drier form of grit which enables easier spreading. It is also a cheaper form of rock salt and has a lower carbon footprint compared to white rock salt.

The benefits of white rock salt are that it is a cleaner product. It does not leave a dirty residue after use and will not stain paving. Generally, it is a more aesthetically pleasing form of grit, that is recommended for use next to main entrances to buildings, such as large office buildings and shopping centres.

When?

The optimum time to use rock salt is before freezing temperatures are forecast, therefore preventing the snow/rain from freezing. Spreading rock salt before the cold temperatures hit will also save on the amount of rock salt needed in order to make surfaces safe.

We would recommend checking the Met Office website for an accurate forecast.

How much?

The amount of rock salt to be used varies depending on the temperature and location. For example, steep hills and sharp bends will benefit from more rock salt compared to flat and straight roads.

However, we recommend that 10-15 grams of rock salt are to be spread per square metre. This amount can increase to 20-40 grams if weather conditions are more severe or if rain has fallen before freezing temperatures are predicted (rainfall will wash away the rock salt).

For example;

  • 500 square metres area = 5000 – 7500 grams of rock salt

Therefore, if you have a 6 cu ft grit bin which holds 175kg, you can cover the area a minimum of 23 times.

  • A football pitch – 7,140 square metres (1.76 acres) = 71400 – 107100 grams of rock salt

Therefore, if you have a giant 50 cu ft grit bin which holds 1400kg, you can cover the area a minimum of 13 times.

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