Technical Article

What is cut edge corrosion?

Cut edge corrosion affects metal roof sheets and wall cladding, particularly where the protective coating has been cut or exposed.

During manufacture, metal cladding is usually coated with a protective finish, such as Plastisol. This coating helps protect the steel underneath from weathering, moisture, and corrosion. However, when sheets are cut to size, the cut edges are often left exposed. Once installed, these exposed edges can become vulnerable to rust and corrosion over time.

Cut edge corrosion commonly occurs on profiled or corrugated metal sheets used on roofs and building elevations. When the exposed steel edge comes into contact with oxygen, water, and pollutants, corrosion can begin. As it develops, the original coating may start to peel back, exposing even more of the metal beneath.

Where does cut edge corrosion usually appear?

Cut edge corrosion is most often found around:
    •   Sheet edges
    •   Eaves
    •   Overlaps between roof sheets
    •   Horizontal laps
    •   Metal gutters
    •   Exposed fixing areas

Horizontal overlaps are particularly vulnerable because water can sit between sheets, allowing corrosion to spread more quickly.

Although corrosion often starts at the edge of a sheet, it can spread as moisture moves beneath the protective coating. If left untreated, this can cause the coating to lift, blister, or peel away from the metal surface.

Guttering can also be affected, especially where it has been poorly installed, damaged, or blocked with debris. When water is allowed to sit against exposed metal edges, corrosion can spread into surrounding roof panels, cladding, or other parts of the building.

Why water makes the problem worse

Water is one of the main causes of cut edge corrosion.

Once the protective coating begins to fail, moisture can reach the exposed steel underneath. This allows rust to form and spread beneath the coating. Over time, the metal can become weaker, more brittle, and more likely to leak.

If corrosion is not treated early, it can eventually lead to:
    •   Peeling or flaking coatings
    •   Exposed bare metal
    •   Rust staining
    •   Water ingress
    •   Weakened roof sheets or cladding
    •   Perforated metal panels
    •   Costly repairs or replacement

In severe cases, the metal cladding can become perforated, causing leaks and further damage to the building.

Why early treatment matters

Cut edge corrosion gets worse over time if it is ignored. What may begin as a small area of exposed metal can develop into a much larger problem, affecting the performance, appearance, and lifespan of the roof or cladding system.

Treating corrosion early helps prevent further deterioration and can reduce the need for more expensive repair work later. However, the best approach is to protect exposed cut edges before corrosion has the chance to develop.

Need help with cut edge corrosion?

If you need to repair existing cut edge corrosion, or you want to protect your metal roof sheets before corrosion starts, Rooflock can help.

Contact the Rooflock Technical Team today for expert advice and to discuss the best solution for your building.