Rust - how does it work??

[p6steve]

This may sound like a really dumb question, but it's one of those I've never really known the answer to and the sort of question everyone wants to know but is too embarassed to ask....and I was crap at physics and chemistry at school!
I've a few patches of rust appearing in the normal places - top of the rear wing just below the vinyl panel, fron wheel arch etc. It's nothing serious yet, but I've always wondered, does the rust continue to form and eat away under the surface even if you're parked in a nice dry garage. I mean does more water need to be introduced to continue the process, or does it just carry on once it's started even though it's in a dry environment. Mine doesn't appear to be getting any worse and I try not to get her wet anymore now i have a garage....
Cheers
Steve.

[arthuy]

Hi Steve,

The simply answer is that once it starts it will conitnue although a car maybe stored in a dry garage the rust will still spread.

The rate at which a car rust depends on how bad it is. There is always moisture in the air and it will get to the rusty bits and if there is mud/dirt on the car before stored then this I would think attracts the moisture.

If I remember rightly Rust is oxygen reacting with the metal. As it reacts it becomes a different chemical, it oxidises? you had oxygen and iron they react and form iron-oxide...or somthing like that. Water increases the rate of which rust spreads because it has oxygen in its make up, (H2O). If my explination is rubbish then someone will correct it.

The dryer a car is the better your chances but rust can lurk underneath and first you know about it is when Mr Mot sticks his thumb through your crossmember..

Arthuy

[JohnGlinn(Cardiff)]

Steve,
Arthuy's explanation sounds good to me!
There are "rust killer" paints that convert existing rust to a different type of oxide (ferrous to ferric maybe- we need a chemist to confirm) which will stop progression of the rot, then paint over the top.
Also, a dehumidifier in the garage will reduce the water content of the atmosphere in the garage to slow down the rusting process to virtually nil, probably not necessary in the summer but during times of condensation, autumn or spring, my dehumidifier pulls a gallon of water out of the air in less than a week! (Invest in a hygrometer also, which measures relative humidity, so that the air in your garage is not too dry otherwise your leather trim and rubber seals will dry out).
Hope all this helps.
Regards, John.