Breaking down Rust

There are 3 main stages of rust on vehicles: Surface Rust, Scale, and Penetration, but first let's discuss exactly how rust is made.  Iron oxide is the technical term for rust, and it is formed when oxygen in the air reacts with the iron. Since vehicles are not typically built out of pure iron due to the inflexibility, tensile strength, and challenges with shaping it, materials such as carbon are added, causing the rust process to accelerate at the molecular level.

Surface Rust:  Paint nicks, cracks, and scratches are the first signs of rust. 

Scale Rust:  At this step, the metal strength of the vehicle is reduced. Dirt, grime, and salt that sticks to (or is trapped in) your vehicle begins to speed up the chemical reaction that causes rust because they act as electrolytes when dissolved in the water. 

Penetrating Rust: Holes in the steel are apparent at this stage.

While many cars are built with coatings and/or are dipped in anti-corrosion agents during the painting process, according to Popular Mechanics, "the road-facing side of the car is basically a sand-blasting cabinet at highway speeds, and those dips and coatings wear off over time."   

The Popular Mechanics article continues on to include ways to remove or reduce rust at each of the stages mentioned above.  To read more about it, click here.