Calibrate, check, recalibrate


National Winter Service Research Group (NWSRG) initiatives have highlighted the effect that changes in salt grade, moisture content or supplier have on the spreader’s performance and the importance of calibrating the spreaders to each individual salt pile. Should the salt type change or vary after the initial manufacturer calibration this should result in recalibration.

The proliferation of de-icing materials such as Thawrox 6, Thawrox 6+, Cleveland Potash, Pre Wet, ABP (agricultural bi products) and a host of imported materials only increases the need for all spreaders to be regularly calibrated and checked.

The differing discharge settings used for a different salt grade could result in a significant amount of material – as much as 40% – being wasted, or more importantly less salt being applied.


The weather can also have a major impact on salt stored unprotected outside. Dry weather will obviously reduce the moisture content of the salt in the pile, giving the salt entirely different characteristics if stored for long periods.

At the NWSRG we are continuing to try to find new ways to detail how crucial it is to check this key service and ensure the correct amount of de-icing material is distributed on the roads.

Our Calibration Working Group, consisting of members from the Steering and Technical Advisory Group, are working towards a simple step-by-step guide to walk practitioners through completing a conformity check on the salt quantity and distribution of their vehicles throughout the winter season.

Static distribution and discharge checks, (as pictured), are key to the step-by-step process along with the recording of the results and subsequent recalibration if required.

Calibration and continuous monitoring/checking of winter service vehicles throughout the season are vital for the provision of a good winter service.

If the spreader’s calibration is inaccurate, the information recorded on vital functions such as spread width and discharge rate will also be inaccurate.

If this goes unnoticed throughout the season and is repeated across several vehicles, a completely misleading picture of actual spreading performance will result.

For maximum efficiency, salt should ideally meet the industry standard regarding moisture. This not only helps to prevent the salt from being blown away in the wind but previous research has also shown that salt at the recommended moisture level initiates a more rapid de-icing process.

In controlled experiments carried out at -50C on a 2mm thick ice sheet, 6mm damp salt performed better than 10mm damp salt and both grades performed better with the addition of water. With the growth in popularity of initiatives such as the Code of Practice Guidance, accurate calibration is more important than ever.

New technology enables highway engineers to be updated daily on all aspects of overnight spreading operations.

Salt stockpiles are automatically adjusted and further supplies ordered if stocks are low. But if the vehicles are poorly calibrated the data will be inaccurate.

Cold Comfort 2018, the 27th Annual Winter Maintenance Conference and Exhibition takes place at the Ricoh Arena, Coventry on 16 and 17 May 2018.

Register your interest today at and we will keep you informed with the Early Bird Discount offers and programme updates.

This article appears in the December/January issue of Highways magazine.

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