Raildust is the common name given to ferrous metal fallout contamination. Often raildust comes from trains and is caused by the train’s wheels on the rails, the electrical pick-up rubbing overhead cables and the effect of the braking mechanism causing tiny particles of metal to fly off into the air. However, this kind of fallout can be caused by any mechanical device that involves metal on metal, including your own car’s brakes. Exhaust fumes will contain some amount of metal, especially from ships and aircraft, foundries and factories.
So already, by pointing out where it comes from, we can see how to avoid it - if you park your car at the railway station, park as far away from the tracks as you can. Metal dust is heavy so it doesn’t float about and travel very far. Just 50 yrds can make a huge difference to the amount of fallout your car will collect in the station car park. Also beware of car parks in ports, airports and next to busy motorways.And of course, if you must use a grinder to sharpen the lawnmower blades, park your car down the street!
No matter what you do, you will get some level of ferrous metal contamination on your car, but why is this a problem? Ferrous metal will rust when it comes into contact with water and the oxidization process causes acids which destroy the binders in your paint. So as the particle rusts, it dissolves the paint underneath it and it then burys it’s self deeper into the paint until it has eaten all the way through to the bodywork, and once that happens, your bodywork begins to rust. It’s important to know how to spot fallout, if you have a light coloured car you will be able to see it as little brown specs, often you can see these against a black coloured car too. A better way to find fallout is to feel for it.if your car is clean, wet an area with clean water and run your fingers over it, if you can feel hard gritty lumps, chances are that that is raildust. (some people do this while having their hand inside a sandwich bag, the fallout will snag on the bad revealing the fallout - this is a good method if you haven’t very sensitive fingertips).
There are two methods of removal. The first is an acid bath… this sounds scary but really isn’t a problem if you are a professional valeter. You wash the car down in an acidic solution, much like a wheel cleaner, this will dissolve the metal particles, and then before the acid can damage the paintwork you wash it off with a soapy solution which will neutralize the acid.
The second method is to use aclay bar (a.k.a. detailing clay) to remove the raildust. Usually a claybar is a synthetic putty which is very sticky and will suck the particles out of the paintwork. A claybar deserves a full entry which can be found here, worth reading folks, because this is a method that you can do yourself!