What is Cut Edge Corrosion and How Do You Fix It?

If you own or manage a building with a profiled metal roof, cut edge corrosion is something you need to know about. It's the single most common cause of premature roof failure on metal-clad buildings in the UK, and if left untreated, it will eventually lead to leaks, structural damage, and a full re-roof. The good news? Caught early, it's straightforward and cost-effective to treat.

What Causes Cut Edge Corrosion?

When profiled metal roof sheets are manufactured, they're coated with a protective finish (plastisol, polyester, or PVF2) on both sides. However, when the sheets are cut to length during manufacturing or installation, the cut edges are left exposed — bare metal with no protective coating.

These exposed edges are where the problem starts. Water runs down the roof profile and collects at the overlaps and drip edges. Over time, this constant exposure to moisture causes the unprotected steel to corrode from the cut edge inward. The corrosion creeps under the factory coating, causing it to delaminate and flake away, exposing more bare metal and accelerating the process.

How to Spot It

Cut edge corrosion is easy to identify if you know what to look for:

• Rust staining — orange/brown staining running down the roof sheets from the overlaps or eaves
• Flaking coating — the factory finish peeling or bubbling at the sheet edges
• Visible rust at laps — corrosion visible at the overlap joints between sheets
• Gutter staining — rust-coloured water in the gutters
• Internal leaks — water ingress at the sheet overlaps (by this stage, it's advanced)

The Stages of Deterioration

Cut edge corrosion progresses through distinct stages. The earlier you catch it, the cheaper and easier it is to treat.

How is Cut Edge Corrosion Treated?

For stages 1–3, cut edge corrosion is treated using a specialist liquid-applied system. The process is:

1. Surface preparation — wire brushing, grinding, or power tool cleaning to remove loose rust and flaking coating back to a sound edge.
2. Rust inhibitor — application of a rust-converting primer that chemically stabilises any remaining corrosion.
3. Edge sealing — a flexible, high-build edge sealant is applied to the prepared cut edges, bridging the gap between sheets and sealing the overlap.
4. Protective coating — a UV-stable, elastomeric topcoat is applied over the sealed edges to provide long-term weathering protection.

In many cases, cut edge corrosion treatment is combined with a full roof coating to provide complete protection to the entire roof surface — not just the edges.

How Much Does Treatment Cost?

Cut edge corrosion treatment is typically priced per linear metre of affected edge. For a typical industrial unit with 500–1,000 linear metres of exposed edges, treatment costs range from £5,000 to £15,000 depending on the severity and access requirements.

Compare this to a full re-roof at £60,000–£120,000 and the business case for early treatment is clear. Every year you delay, the corrosion advances and the cost of repair increases.

Prevention

The best way to prevent cut edge corrosion is to coat the roof before it starts. If your building is 10+ years old and has never been coated, it's worth getting a survey done to check the condition of the cut edges before problems develop.

Regular gutter cleaning also helps — blocked gutters cause water to back up and sit against the sheet edges, accelerating corrosion.

Key Takeaways

• Cut edge corrosion affects virtually all profiled metal roofs over 10 years old
• It's caused by unprotected cut edges being exposed to moisture
• Early treatment is simple and cost-effective — delay makes it exponentially more expensive
• A proper survey will identify the stage and recommend the right treatment
• Treatment extends roof life by 20+ years at a fraction of re-roofing cost