Understanding Rust: What Is Corrosion?
Beat your enemy by understanding it. Here’s our plain-English take on what rust actually is, why steel is so determined to corrode, and how that knowledge points straight to the right way to protect it. (No offence intended to any metallurgists reading — this is the practical version.)
What is rust?
Iron and steel aren’t found free in nature — they’re extracted from iron ore in a blast furnace or electric oven, a process that pumps huge amounts of energy into the metal. Steel spends the rest of its life trying to release that stored-up energy and return to its natural, stable form: iron oxide. That iron oxide is what we call rust.
Noble metals vs base metals
Some metals — gold, for instance — are found free in nature. They’re “noble”: stable, and in no hurry to change. The Saxon gold brooch pictured at the top of this page is over a thousand years old with no sign of corrosion; you can still pan for gold in a river and pick it up from the ground. Iron sits at the other end of the scale. It’s a “base” metal that had to be forced out of its ore, so it’s permanently trying to revert — and that’s the whole problem.
Galvanic corrosion: dissimilar metals
Rank metals by nobility and you get the galvanic series. Connect two of them through an electrolyte — water — and the less noble metal is consumed to protect the more noble one. It’s used deliberately on ships: zinc sacrificial anodes are bolted below the waterline so the zinc corrodes instead of the steel hull. That’s cathodic protection, and the zinc is used up while the steel stays intact.
Steel is a charged battery
Here’s the mental picture that ties it together. The energy trapped in steel makes it behave like a charged battery, with both anodic (+) and cathodic (−) areas in its structure. Add moisture — the electrolyte — and it discharges, exactly like a torch battery lighting a bulb. As the energy is released, the anodic areas are consumed: the steel rusts. Some areas are more reactive than others, which is why corrosion so often takes hold in seams and crevices where damp sits and can’t escape.
The three ways to beat corrosion
Once you see rust as an electrochemical reaction, the defences make sense — there are three, and each maps to a Rustbuster product.
Barrier protection
Seal the steel away from air and moisture with a coating that’s hard for them to get through — a thick, low-permeability paint such as an epoxy or polyurethane. In the Rustbuster range that’s Epoxy Mastic paints for surfaces, and Corrolan for inside cavities and box sections.
Passivation
Stop the reaction chemically. Rust-inhibitive pigments react with the steel and any moisture in the film to neutralise the corrosion. That’s exactly what FE-123 Rust Converter does — it converts active rust into a stable, paintable surface.
Cathodic protection
Give the steel something less noble to sacrifice itself instead. A coating loaded with metallic pigment — usually zinc — corrodes in place of the steel, the same way a sacrificial anode protects a ship’s hull. Zinc Rich Epoxy works on this principle.
Understanding rust — FAQs
What actually is rust?
Rust is what you get when iron corrodes. Iron and steel are extracted from iron ore using huge amounts of energy, and they naturally want to release that energy and return to their stable form — iron oxide, which we call rust.
Why do some metals not rust?
Metals found free in nature, like gold, are “noble” and stable — which is why a thousand-year-old gold brooch shows no corrosion. Iron is a “base” metal that was forced out of its ore, so it’s always trying to revert.
Why does steel rust faster in seams and crevices?
Steel behaves like a charged battery with anodic and cathodic areas. Add moisture and it discharges, corroding the anodic areas. Trapped damp in seams and crevices keeps that reaction going, which is why rust so often starts there.
Can you mix steel and aluminium safely?
Only with care. When two dissimilar metals touch through an electrolyte, the less noble one corrodes — classic galvanic corrosion, as seen where aluminium panels meet steel frames. Isolate them (for example with plastic sheaths on fixings) to reduce the contact.
Now you know the enemy, beat it properly. See our 10 steps to complete rust protection, how to use FE-123 rust converter, and our lanolin rust-proofing guide.
