The Hidden Science of Cut Edge Corrosion: What You Didn’t Know About Rust

Cut edge corrosion is a familiar foe in the world of metal cladding, and if you’ve followed our blog at Cladding Coatings, you’ll know we’ve covered its causes, consequences, and cures extensively. But beneath the peeling paint and rust streaks lies a fascinating world of chemistry and environmental science that’s often overlooked. Here’s the lesser-known scientific mechanisms behind cut edge corrosion and reveal some surprising facts that might change how you think about rust.

At its core, cut edge corrosion is an electrochemical reaction. When the protective coating on metal cladding is cut, typically during manufacture or installation, the exposed edge becomes vulnerable to oxygen and moisture. This triggers oxidation, where iron atoms lose electrons and form iron oxide (rust).

But here’s the twist: corrosion isn’t just a simple reaction. It’s a localised electrochemical cell. The exposed metal acts as an anode, while nearby coated areas become cathodes. Moisture acts as an electrolyte, allowing electrons to flow and accelerating the rusting process. This is why corrosion often starts at the cut edge and spreads inward; it’s a self-sustaining reaction.

The UK’s climate is a perfect storm for corrosion. High humidity, frequent rainfall, and temperature swings create ideal conditions for moisture to linger on metal surfaces. Add in coastal winds carrying salt particles, and you’ve got chloride ions that dramatically speed up the breakdown of protective coatings.

Salt doesn’t just make metal rust faster, it disrupts the oxide layer that normally forms on metal surfaces, allowing corrosion to penetrate deeper. That’s why buildings near the coast or in high-rainfall regions are especially prone to cut edge corrosion.

Even if a metal sheet looks intact, microscopic cracks in the coating can act as entry points for moisture and oxygen. Once water seeps in, it can cause the coating to delaminate, peeling back from the surface and exposing more metal. This is often seen at the cut edge, where mechanical stress and poor coating adhesion make the problem worse.

Interestingly, the corrosion process can begin before any visible damage appears. By the time rust streaks are noticeable, the underlying metal may already be compromised.

If your cladding system involves multiple metals, for example, steel fasteners on aluminium panels, you might be inviting galvanic corrosion. This occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte (like rainwater). One metal becomes the sacrificial anode and corrodes faster than it would alone.

In cladding systems, this can mean that the cut edge corrodes more rapidly if it’s adjacent to a different metal. It’s a silent accelerant that’s often overlooked during installation.

Rust isn’t just red: Depending on the environmental conditions, rust can appear yellow, brown, or even green. These colours indicate different types of iron oxides and hydroxides.

Rust expands: Iron oxide occupies more volume than the original metal, which means rust can physically push apart coatings and fasteners, worsening structural damage.

Rust is conductive: While not as conductive as metal, rust can still carry electrical current, which can perpetuate electrochemical reactions and lead to further corrosion.

Corrosion can be contagious: Once rust starts at one cut edge, it can spread to adjacent panels through moisture migration and electrochemical coupling.

While protective coatings are essential, science shows that prevention must be multi-layered. Here’s what works best:

• Edge sealing: Applying specialist sealants to cut edges prevents moisture ingress and stops the electrochemical reaction before it starts.
• Regular inspections: Catching corrosion early before delamination or rust streaks appear can save thousands in repairs.
• Smart material choices: Using compatible metals and corrosion-resistant fasteners reduces the risk of galvanic corrosion.
• Environmental awareness: Buildings in coastal or industrial zones should consider enhanced protective systems.

Cut edge corrosion may start small, but its scientific complexity makes it a formidable challenge. At Cladding Coatings, we combine technical expertise with cutting-edge materials to stop corrosion in its tracks. Understanding the science behind rust empowers us and our clients to make smarter, longer-lasting decisions.

If your building shows signs of cut edge corrosion, don’t wait for the science to run its course. Contact us today for a tailored inspection and treatment plan that protects your property from the inside out.