CORROSION We all recognise rust when it starts to a pear around p certain parts of our cars anatomy. Then, before we are aware, it's too late and metal has been replaced by a very poor substitute. The result is costly, can be dangerous and will not win the car any beauty awards!
The only way to beat rust is to prevent it in the first place or at the very least slow it down. To do this, first of all we must realise how rust is formed.
Think of a piece of metal with a bead of water sitting on top.
The metal below the water is starved of air and is called anodic. The metal outside this area is known as cathodic. An electrolytic action is formed between these two conditions and it is this process that causes corrosion. There are acceleration factors involved such as dirt, grit or salt. These can be contained in the water and will increase the conductivity.
So basically rust is formed by an electrochemical reaction.
Bear in mind that rain needn't necessarily be the water factor involved in the process - condensation plays its role too.
Obviously it doesn't take much logic to understand how rust can be prevented in the first place. The metal work of the car has to be protected from moisture and air. This protection is partly taken care of by the car manufacturer when the car is put together - paint on the outside and special inhibitors used on the inside. However, the rust protection is only as good as the application of these materials and one spot missed means that rust will accelerate all the more in this particular spot.
The importance of regular washing and touching up paintwork play there part in rust protection. For example, regular hosing down of the underneath of the car can help prevent any build up of mud forming in certain areas. Mud can act like a damp sponge during wet weather so that you have a constant moisture problem even during dry spells. You'll find that common rust problems on particular models usually originate from mud-traps.
You can always go one step further and improve on the manufacturers rust protection by tackling your own rustproofing.
This involves applying light viscosity waterdisplacing material inside all the box sections and/or applying underbody sealant.
There are various kits on the market designed specifically for the keen DIY motorist and even if you don't treat all the box sections it is worthwhile devoting some time to protecting the rust prone areas of your particular car.
An important part of protection is treating the car with an underbody sealant. Here preparation is of the utmost importance because if the sealant doesn't attach firmly to the car body then the air gap between seal and metal can help accelerate corrosion rather than prevent it.
First of all the car will have to be thoroughly cleaned underneath. A high pressure hose is obviously helpful in removing dirt but better still is to have the car steam cleaned first.
Apply an underbody sealant is a dirty job and you should be well prepared with old clothes, gloves and a hat. If you are venturing underneath the car and it has to be jacked up then make certain that it is well supported on axle stands.
After thoroughly cleaning the underside you should go over stubborn dirt or caked mud with a good fine wire brush. The important thing is that the surface to be treated is absolutely clear of any foreign matter. For good application of underbody sealant use a cheap paint brush. It is important that the sealant used will remain flexible and will not chip or flake at a later date. Obviously care will have to be taken not to cover moving parts such as the drive shafts, handbrake linkages, etc. If necessary then mask these areas first.
The first part of this section on corrosion concentrates on the matter of protection. Which is fine before corrosion takes place. But what happens if corrosion has already taken a hold?
It can be a costly business when corrosion dictates the vehicle being taken off the road through an MoT failure. As already explained in 'Passing the MoT' page at the beginning of this Repair Manual, an MoT tester win check for damage or corrosion in or on a vehicle that is likely to render it unsafe.
With the Mini, the tester will pay special attention to the front and rear sub-frames and the sub-frame mountings, side sills, inner support rib and the floor, the latter especially where the steering rack is mounted. Also hell check the seat belt mounting areas.
Having checked and identified the important areas, the MoT tester will check the extent or level of suspect corrosion.
He should do this by pressing hard against the area and testing the amount of 'give' which results. Often he will also tap the component lightly (it should not be necessary to subject the area to heavy blows), listening for differences in sound which will result from unaffected metal compared with corroded metal.