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The problem with road salt…

October 3rd, 2011

Road salt accelerates metal corrosion processes, which is bad news for cars.

…is that it accelerates metal corrosion processes, which is bad news for cars. Add in the wider environmental damage it causes, particularly to waterways and man-made structures, and it becomes clear that its widespread use as a road de-icer during the winter months is controversial to say the least. Last autumn, we posted an article about road salt and the need for car care enthusiasts to protect their cars against it. Despite the unusually good weather we are currently experiencing, it won’t be long now until the nights draw in, temperatures drop and the gritting lorries make an appearance. With this in mind, we thought it would be useful to revive last year’s article and refresh your memory about the importance of proper winter preparation. So, without further ado…

…IS YOUR CAR READY FOR WINTER?

Is your car ready for winter?

October 5th, 2010

This month we were originally planning to post John’s thoughts about the polishing process but, given the time of year, we thought it more appropriate to address the issue of winter preparation, and in particular why and how you should protect your car if you decide to run it all year round. Indeed, with the nights already drawing in and the brutality of last winter still fresh in our minds, now is the time to get busy before the temperature drops and the gritting lorries make an appearance (assuming your local council hasn’t completely run out of money)…

Why is winter so brutal on our cars?

In a nutshell, road salt. Ever since the 1930s, road salt has been used extensively during the winter months in the UK to lower the freezing point of moisture on road surfaces, thus helping to prevent lethal ice from forming and causing existing snow and ice to melt. Indeed, given the instant mobility demands of modern day drivers and the fact that relatively few people would ever consider fitting winter tyres, road salt remains a cost effective option for managing road safety. However, road salt is far less welcome from the point of view of motoring enthusiasts and the wider environment in terms of the long-term damage it causes to cars and man-made structures; salt deposits tend to harbour moisture and vastly accelerate metal corrosion processes.

Road salt; the real reason why winter is so brutal on our cars

How does road salt improve road safety?

Although the UK’s winter climate is not particularly severe, the combination of temperatures hovering around freezing and frequent precipitation means that icing up of roads is commonplace. In the rest of northern Europe, where winters are typically harder, many countries enforce the use of winter tyres in order to ensure better traction under such conditions. However, in the UK, where winter weather can be much more variable, drivers have never been required or encouraged to switch tyres on a seasonal basis, and as a result road safety has become dependent upon de-icing practices instead. Whilst numerous de-icing methods exist, road salt is by far the most readily available and cost-effective option open to road maintenance and traffic safety authorities, and is also easy to store, handle, and apply.

Road salt works by lowering the freezing point of water. To understand how it does this, we need to know a few things about the properties of water and ice. Water is made of tiny molecules that are always in motion. These molecules move faster when water is warm and slower when water is cold. Ice forms when the temperature is cold enough for the molecules to slow down and form bonds with each other; normally, this happens at 0 °C. On the surface of ice, water is constantly melting and freezing as some water molecules break free of the ice lattice while others are captured. This happens at such a tiny scale that you cannot see it; you just see the overall effect. If more molecules are melting than freezing, you will see the ice begin to melt. Conversely, if more molecules are freezing than melting, you will see the ice thicken and spread.

When road salt dissolves in water, it separates into individual sodium and chloride ions, and it is these ions that lower the freezing point of water (typically down to around -9°C). When you spread road salt on top of ice, its hygroscopic nature attracts water molecules that have broken free of the ice lattice, which in turn then dissolve a little bit of the salt. The dissolved salt ions then inhibit the freezing process (by causing fewer water molecules to come into contact with the ice lattice, and by interfering with the molecular bonding process itself), so these molecules do not refreeze. As more water molecules break free, they gradually dissolve more of the salt, which in turn reinforces the melting process. However, if the temperature falls below -9°C the water molecules will begin to bond with each again regardless of salt interference, resulting in ice reforming.

Road salt is extracted in a brown, gravel-like form from underground mines

Why is road salt so damaging to cars?

Technically speaking, road salt is hygroscopic in nature, which means that it attracts, absorbs and retains moisture wherever it is deposited. Road salt accumulation on vehicle surfaces is therefore highly undesirable, since dampness is known to accelerate electrochemical oxidation, i.e. the rusting of iron containing metal components. In a nutshell, whenever iron comes into contact with water in the presence of air, oxygen is liberated from the water and then used to break down the iron into iron oxides (which are typically red or orange in colour, hence the term rust). Modern factory applied paint systems offer excellent protection against rusting, but once treated surfaces are breached by surface weathering or stone chip damage, corrosion can quickly set in. Suspension assemblies, brake components, steering systems, drive trains and sub-frames are all highly susceptible to this type of corrosion.

In addition to its hydroscopic nature, dissolved road salt also transforms water into a highly effective electrolyte, which not only accelerates the speed of rusting, but also enables galvanic corrosion to occur. Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially when in electrical contact with a different type of metal. In order for galvanic corrosion to occur, both an electrically conductive path and an ionically conductive path are necessary. This effects a galvanic couple where the more active metal corrodes at an accelerated rate and the more noble metal corrodes at a retarded rate. On cars, this type of corrosion is most common on alloy wheels with stone chip or kerbing damage, as iron-rich brake dust sitting on the damaged rim surface initiates more rapid corrosion of the aluminium alloy making up the wheel beneath. In the presence of road salt, such corrosion can proceed very quickly indeed.

A classic example of galvanic corrosion setting in on an exposed engine cover

How can I better protect my car against road salt?

Over the last twenty years manufacturers have invested heavily in improved multi-layer paint systems that are now much better able to withstand environmental stresses and the damaging effects of road salt; corrosion warranties now typically extend to twelve years or more, and it is uncommon to see cars with visibly rusting bodywork on the road. However, if you take a closer look at the underside of most cars, you will typically find evidence of fairly widespread surface corrosion, particularly on suspension assemblies, brake components, steering systems and the sub-frame itself. This arises because such surfaces are highly susceptible to surface damage from stones and road debris, and once protective paint coatings are breached surface corrosion quickly sets in. In order to properly protect our cars, we should therefore remember to care not only for the bodywork and wheels, but also for exposed surfaces in wheel arches and beneath the car as well.

Starting with the bodywork, in most cases a late autumn application of either a high quality synthetic polymer sealant or a high quality natural carnauba wax will be sufficient to protect the paint system properly through the winter months; modern paint systems are very advanced and able to withstand environmental stresses very well on their own. The only caveat is that care should be taken to perform stone chip repairs as soon as possible after they are noticed, otherwise localised corrosion can set in. Various options exist with regard to making stone chip repairs, ranging from simple do it yourself touching in through to employing bodyshop services to respray the affected panel. Whichever option you choose, act quickly to repair penetrating damage, or at the very least make sure you apply sealant or wax protection as soon as possible – maintaining a barrier against moisture is critical in terms of corrosion prevention.

When it comes to choosing what sealant or wax to use for winter protection, there are plenty of options available on the market, based on criteria such as cost, durability, ease of application, etc. In order to make the selection process a little bit easier, we would advise the following: (i) prioritise durability if you want the resulting finish to last all the way through to spring without being topped up (ii) prioritise ease of application if you knowingly want to top up the finish periodically throughout the winter months. In the former case, long-life paste waxes such as those made by Collinite are ideal, as are long-life liquid nanotechnology sealants such as Nanolex Premium Paint & Alloy Sealant and Wolf’s Chemicals Nano Paint Sealant (Body Wrap). In the latter case, we would strongly avoid choosing any kind of wax as they tend to be difficult to apply in cold, damp weather – a far better choice would be a sprayable acrylic sealant, such as Werkstat Acrylic Jett Trigger or Auto Finesse Tough Coat, both of which remain perfectly useable right down to freezing point.

Moving on to your wheels, I can’t stress enough how important it is to clean your wheels regularly throughout the winter months; preferably at least once a week using a non-aggressive wheel cleaner, such as R222 Wheel Cleaner (Regular). It doesn’t matter how hard it is raining or how cold it is, just get your coat on and give your wheels a quick wash and don’t worry about drying them off; just make sure you remove all of the brake dust and road salt. It only takes a few weeks for galvanic corrosion to set in on damaged rims crusted with brake dust and road salt, and in the winter many weekends can pass by without a single nice day, so avoid procrastination at all costs. We recommend spending a full day removing, cleaning and protecting your wheels prior to the onset of the first frost. Multiple layers of a good quality high temperature resistant wheel sealant, such as Swissvax Autobahn, should be applied at this time, and top up applications should be added as and when opportunities arise throughout the winter months.

When it comes to caring for exposed surfaces in wheel arches and beneath the car, a combination of practices are recommended. Firstly, synthetic polymer sealant or natural carnauba wax coatings should be applied periodically to all smooth textured painted and bare metal surfaces, including springs, damper bodies, brake calipers, control arms and the sub-frame itself (if a factory applied layer of underseal is not present). Industrial grade products with proven durability are ideal in this respect, and we tend to favour Collinite Insulator Wax and Blackfire All Metal Sealant (which is ideal for painted surfaces too). Secondly, such surfaces should be cleaned regularly using a pressure washer, in order to prevent salt deposits and grime from building up. This isn’t a particularly pleasant job, but attachments are available for most popular makes of pressure washer that make underbody access easier. Time spent washing such surfaces is time well spent, as it will help to prevent corrosion from setting in.

If you wish to go one step further, you could also look into an aftermarket underseal treatment. These range from effective do it yourself products such as CarPlan Tetroseal through to professionally applied Waxoyl treatments (although the latter is an increasingly hard to find service, reflecting the reduced demand for such treatments in recent years as a direct result of improvements to modern paint systems in terms of corrosion resistance). However, even if a virtually bomb-proof layer of underseal is added, care should still be taken to wash off salt and grime on a regular basis. As the saying goes, prevention is better than cure, particularly on surfaces subject to the worst our roads throw at them.

Recommended products for protection against road salt and winter grime

What else can I do to lessen the impact of winter on my car?

In addition to caring for your car and preparing it properly, you can also lessen the impact of winter in other ways too. Your driving style can make a profound difference in terms of the potential to acquire stone chip damage. If you always drive closely to the car in front you run the risk of regularly being sand-blasted with grit and other debris, much of which will progressively chip the paint on the front end of your car. It is far more sensible in the winter months to leave a bigger gap than normal to the car in front, not just from a braking perspective, but also to minimise the amount of front end impact damage from grit and other road debris. Fitting mud flaps can also help to greatly reduce stone chip damage to side skirts and lower panels, but do be aware that this also provides additional nooks and crannies for salt accumulation, so make sure you wash around them very carefully!

Going off on a slight tangent, I am also a firm believer that fitting dedicated winter tyres makes good sense, not just from a handling and safety point of view, but also from a cultural standpoint. If enough of us start doing this voluntarily then the government may yet realise that winter tyre legislation makes more sense than throwing down millions of tonnes of road salt each year. If we can remove road salt from the winter equation then our cars and roads should stay in better condition for longer in the future, potentially saving ourselves and the country a significant amount of money in the long run. In addition, when temperatures drop below -9°C or when significant amounts of fresh snow falls then road salt becomes ineffective anyway. Surely it would be better from a road safety perspective if everyone was permanently and properly equipped for all possible conditions throughout the winter months?