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Road salt and corrosion - Q&As

Side of rusty van

Why do classic cars rust?

The majority of cars are constructed using steel, a material primarily composed of iron with a small amount of carbon. Iron corrodes due to its inherent tendency to return to its natural state, known as the ‘thermodynamically favoured state’. Nearly all metals tend to combine with oxygen to form metal oxides. When found in the ground, these metal oxides are referred to as ores. Consequently, the rust found on a car panel is essentially akin to iron ore. Under completely dry conditions, iron rusts at a slow pace, but in the presence of water iron atoms readily combine with oxygen to form an oxide.

Why does road salt increase rusting?

Steel components exhibit accelerated rusting when exposed to water rich in electrolytes. Electrolytes are chemicals that enable the conduction of electricity when dissolved in water. Generally speaking, steel rusts approximately five times faster in saltwater compared to freshwater. Cars are also subject to attack from acids formed from road contaminants and even stray battery currents and dissimilar metals can contribute to the electrolysis process. Consequently, if your car comes into contact with saltwater, it is advisable to clean it thoroughly using ample amounts of freshwater to mitigate the effects of corrosion.

Electrolyte solution
Rust bubble on bodywork

What is the chemical process that causes rust?

Rusting is classified by scientists as a ‘redox reaction’. In redox reactions, certain atoms gain electrons while others lose electrons. In the case of rusting, iron atoms release electrons while oxygen atoms gain electrons. The iron acts as a negative anode, and the oxygen serves as a positive cathode. Water, acting as an electrolyte solution, facilitates the movement of ions between the cathode and the anode. Due to its higher electrolyte content, saltwater enables faster ion movement. Once the redox reaction takes place, the iron (Fe) undergoes a transformation into hydrated ferric oxide (Fe2O3·H2O).

Why are roads salted?

Salt is commonly applied to roads because it effectively lowers the freezing point of water. While fresh water freezes at 0 degrees Celsius, a 20% salt solution only freezes at -16 degrees Celsius. As a result, when snow melts and mixes with salt, it takes longer for the resulting solution to solidify into ice. When salt dissolves, it separates into sodium ions and chloride ions, which disperse within the water. These ions, in essence, act to separate the water molecules and hinder the formation of ice. Consequently, when road salt effectively fulfils its purpose, it introduces a significant number of free-floating ions. So when you drive on a salt treated road your tyres spray your car in this a ion rich brine.

Back of gritter lorry
Huge pile of road salt

What is road salt?

Road salt, also known as halite, is a naturally occurring mineral. The largest rock salt mine in the UK is in Winsford, Cheshire. Halite shares a fundamental similarity with table salt in that both are primarily composed of sodium chloride. However, there are significant differences between the two. While table salt undergoes  purification processes to meet strict standards for human consumption, road salt is typically sourced directly from mines. Impurities like like calcium, magnesium, potassium give road salt its distinctive grey or brownish appearance.

Is road salt bad for the environment?

Our Environment Agency don’t believe road salt has a significant impact on the UK environment. They claim the rapid dilution of road salt mitigates any potentially negative effects on wildlife.

However, the situation differs in the United States (and Canada) where certain states apply road salt for prolonged periods. Extensive studies conducted there have confirmed road salt can harm vegetation and wildlife. Surveys conducted alongside US highways have demonstrated the accumulation of salt in wetland areas.

Salt being spread on road
Painting to protect against rust

How can you stop rust?

Stopping rust is very difficult, a more relevant question is how can you slow rust down. The issue with steel is that unlike other metals that corrode, rust does not form a protective barrier but continues to erode the material. Consequently, the key to slowing down rusting lies in shielding the steel from the surrounding atmosphere.

There are several effective barriers that can be utilized, common ones include paint, oil, grease, wax and lacquer. Galvanizing is another technique where a thin layer of zinc is added to the steel to forms a protective barrier as it oxidizes. Chrome plating offers a further layer of defence by coating the steel with a more durable and robust metal.

Our wash wands make it super easy to rinse salt off your classic.



The starter kit comes with two Wands – one for cleaning bodywork and one for cleaning under your car. PLUS 100ml samples of our Road Rinse & Winter Wash Shampoo and a small super-absorbent natural chamois.



The complete kit comes with the same two wands. PLUS 500mls of Road Rinse, 500mls of Winter Wash Shampoo and a full-sized super absorbent natural chamois.



The pro kit comes with the same items as the complete kit BUT the long underbody wand is replaced by a wheeled trolley cleaner, which avoids the need to bend.

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