Salt: The bane of every classic car owner’s existence. When the first glints of sun appear in late January that familiar desire to take your classic for a drive returns. Then you find that the temperature fell below freezing last night and the council had the gritters out. Good for your gran’s safety, not so much for the integrity of your classic car. After seeing many treasured classics at the Sunday Scramble in January it seemed sensible to do some more digging on the effects salted roads have on classic cars.
Grit consists of mined chunks of rock salt or sodium chloride which when mixed with moisture on our roads combine to create a saline solution. The presence of salt amongst water molecules prevents the molecules from aligning in the correct formation effectively lowering the freezing point of water. Hence, salt spreading is used as a preventative measure to decrease ice formation on our roads to ensure the safety of cars and pedestrians.
Over 1 million tonnes of the stuff are spread on UK roads every year. Unfortunately, salt spreading has a potentially significant impact on cars as it accelerates the rate of rust formation. Rust is an oxidation reaction that occurs when ferrous metals, most commonly steel in cars, react with oxygen and moisture. Adding salt to the equation speeds up the reaction as salt acts as medium through which metal loses its electrons more quickly.
Modern cars are significantly more resistant to rust due to advances in paint, lubricants, design and especially materials. Plastic undertrays now shield vast sections of the underside of cars and line most wheel arches. Classic cars however, are not so well protected from this troublesome reaction.
Until the late 1980’s many automotive manufacturers still used cheap unprotected steel to build cars, stuck in the post war mindset that a layer of paint provided enough protection from rust – which it didn’t. Many body panels stored poorly before assembly had already begun to rust, paint often didn’t reach internal parts of box sections and so on. Only when rust began to affect brand reputations and profit margins did the big manufacturers begin to adapt. Bodies were dipped in primer initially which helped but the biggest step forward was galvanising whereby steel parts are coated in a thin layer of corrosion resistant zinc.