Reducing Rust

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Not helped by most classics having negligible protection from new, Rob Marshall advises on how to reduce the chance of rust emerging and what can be done, should corrosion be found

Ashes-to-ashes, dust-to-dust; as cars are made from steel, they will rust. While I hope that Anglicans will not chastise me too much for the little addition to their funeral passage, the philosophy of us all returning to a base state eventually is also relevant to cars. Most car bodies are made from steel, a metal that results from applying energy, during the smelting of iron ore, which is rich in iron oxide (rust). However, with the help of water, oxygen, and sufficient time, the applied energy leeches out and the metal returns to its natural, crumbly state.

Should you be using your classic all year-round, be aware that the process is accelerated by salt, which is applied regularly to the roads during wintertime.

PREVENTION IS BETTER THAN CURE

Logically, the most practical way of protecting steel-bodied vehicles is to shield it from both oxygen and water. Galvanising, which applies another metal over the bare steel (to enable ‘sacrificial corrosion’ to occur), is performed during the raw material’s manufacturing process and, while the majority of classics do not benefit from their steel panels being protected by another metal, many models feature chromium-plated bumpers. Ironically, should a pin-hole develop, the steel beneath will corrode even faster, sacrificing itself to preserve the plating. Paint provides an inexpensive barrier from both moisture and oxygen but the coating is easier to damage.

As the underside of a car is vulnerable to being pelted with salt and grit, a tough but flexible rubber, or bitumen-based, underseal might be applied but that can also dry out and trap moisture, pinning the dampness against the steel. Condensation can also lurk within the vehicle’s box-sections, resulting in the car rusting from the inside out. A thin, protective wax, or oil, can be sprayed into these hollow sections, to prevent the damp from making contact with the metal.

Inspecting the underbody regularly is essential. Yet, unless the dark underseal has peeled off, it can be tricky to spot rust. Should you not be a fan of the gungy, black finish, I have found that hard-setting, two-pack, modern coatings, such as the Epoxy Mastic (sold by Rustbuster, 01775 761 222), provide exemplary underbody protection that can be over-painted in body colour. This is not necessarily to keep the Concours judges on your side but it has the practical advantage of allowing you to spot any developing rust, prior to it spreading. Yet, you will need to de-grease the underside of any previous oil-based underseal thoroughly, prior to applying the new coating, which can be both time consuming and messy.

Incidentally, I do not recommend that you use certain air-drying coatings, such as Hammerite’s popular metal paint, because it tends to chip off too readily, when used beneath a car and require regular maintenance. Excellent, air-drying, rubber-based stone-chip products are available but they tend to leave a mottled finish, when applied with a Schutz gun.

While many owners report great success, spraying engine oil into the insides of doors and box-sections, high-quality cavity waxes possess specialised corrosion inhibitors and do not need regular topping-up, plus you will not be irritated by the occasional whiff of old oil.

Waxoyl tends to be the most recognised but alternatives are available to the classic enthusiast, such as Dinitrol’s 3125 and Noxudol 700 but do not discount alternatives from respected companies, such as Würth, Sika and Bilt Hamber.

Topping-up, or even adding to, this protection, prior to corrosion taking hold, is the best and least expensive method of rust protection.

Being both cheap and easy, washing the paintwork and hosing the underbody (not forgetting the wheel arches) regularly is vital, because it prevents accumulated mud and salt from holding moisture against the metal. Applying a wax not only improves your car’s kerb appeal but it also helps to repel water, albeit for a limited period. An inexpensive wax might give protection for several months, whereas a more expensive type, will last longer.

‘CORRODERE’ – TO GNAW INTO PIECES

The meaning of the Latin word, from which ‘corrosion’ originates, appears to be well chosen, when viewing rusted steel, because the damaged surface appears as if it is being eaten away, even though the steel is really reverting back to its natural state. The resulting iron oxide also takes up more mass, which will cause any paint, which might be applied over it, to swell and blister, until the coating fails completely. Unlike corrosion on aluminium, iron oxide does not protect the underlying steel from further rusting; the process is accelerated instead, because further moisture is drawn into the metal.

If you discover rust, do simply not plaster paint over it, because the coating will not halt the deterioration. Additionally, certain coatings, such as body filler and filler primer, absorb moisture and will hold it against the bare steel. The best method is to remove all of the brown iron oxide completely but, should you jab a screwdriver at the rusty area and it passes through, the steel has become extremely weak and the only option would be to cut out the rusty zone and weld-in new material.

In other cases, the first step is to remove as much surface rust as you can, by grinding it out, preferably with a flap-disc, or a wire brush, fitted to an angle-grinder.

You will sacrifice some sound metal in this process but all is not lost, if you cannot access the area, because you can use a chemical rust remover instead. Some versions, including professional products, are very acidic and they require washing off afterwards.

Other types, such as Bilt Hamber’s (01277 658 899) Deox gel, are more DIY user-friendly but several time-consuming applications might be needed. As the bare metal will start rusting again almost instantly, apply a rust converter, as soon as the area has dried.

While Hammerite’s Kurust is widely available, it is expensive, especially as more heavy-duty products, such as Rustbuster’s FE-123 or Bilt Hamber’s Hydrate 80 can be obtained from specialists, for a similar outlay.

All of these products convert any remaining iron oxide into a more stable substance, while forming a protective barrier against any moisture ingress, which can be over-painted with the anti-corrosion paint of your choice, from underseal to Epoxy Mastic, or even an etch primer, prior to applying a top coat.

Banishing the dreaded ‘car cancer’ is far from easy but, with regular inspections and washing, coupled with applying the latest removers, converters and coatings, there is no reason why your classic’s bodywork should not emerge from the winter in rust-free health.

THE UNITARY BODY: KEEP IT BEAUTIFUL

Early motorists were not overly worried about rust, one reason for which was that a separate chassis tended to be made from steel thick enough to shrug off corrosion for at least several decades and rust in the body, bolted to it, tended not to weaken the structure. Despite his genius, the US engineer, Edward Budd, can be ‘blamed’ for ensuring that a chassis- less car body could be made out of steel thin enough to be cut with a pair of domestic scissors, because the shape, in which the material is pressed, provides the strength. Budd also influenced European carmakers, most notably André Citroën, with whom he worked to develop the unitary-bodied Traction Avant, which did away with the conventional separate chassis. Due to the thin steel pressings, Budd realised that, should any part of the unitary body be affected by rust, its entire strength would be compromised. He experimented later with stainless steel, although the fruits of his labours benefited railway locomotives and not the motor car.