What Makes Rust Stick to Metal?

Rust is basically metal’s version of getting a very stubborn sunburn that turns into scabs which eventually fall off to reveal more skin underneath.

When iron or steel meets water and oxygen, they get together for a chemical hug called oxidation. Imagine leaving a shiny bicycle out in the rain. The water acts like a little helper that grabs onto the metal atoms, and air’s oxygen joins the party. Together, they form a new substance called iron oxide, which is what we call rust. This isn't just a dusty layer on top; it starts to flake off because it takes up more space than the original metal does. Think of trying to wear a coat that suddenly grows too big for you. As the flakes fall away, fresh metal is exposed to more water and air, so the rust spreads deeper inside until the whole object crumbles.

Rust sticks because it is porous. Unlike paint or wax which sits smoothly on top of a surface like a blanket, rust has tiny holes in it, much like a sponge made of rough crumbs. Because of these holes, water can seep right through the crust to reach the healthy metal hiding below. This allows the rusting process to continue eating away at the steel from the inside out.

You might notice that gold doesn’t get rusty even after centuries in sand. That is because gold is noble, meaning it doesn’t like mixing with oxygen as much as iron does. Iron, however, is very eager to react. If you want to stop this, you can put a barrier between the metal and the air. Painting your fence or coating it with oil creates a waterproof shield. It’s like putting plastic wrap over a cut apple so it doesn’t turn brown. Without that protection, the hungry rust will keep eating until nothing is left.