Cut Edge Corrosion Explained

Many industrial roofs are constructed from profiled steel sheets, protected by a factory-applied coating. This coating is designed to shield the steel from weather, moisture and environmental exposure. However, where the sheets are cut during manufacture, the exposed edges remain more vulnerable over time.

These vulnerable areas are typically found at sheet laps, edges and fixings. As the original protection begins to break down, corrosion can develop. For surveyors and property professionals, understanding how cut edge corrosion forms – and how it can be treated, is essential to extending the life of industrial roofs, supporting planned maintenance strategies and reducing the risk of costly dilapidation issues.

What is cut edge corrosion?

Cut edge corrosion occurs when the protective coating on profiled steel roof sheets begins to fail at the exposed edges of the sheet.

Once the coating breaks down, the steel beneath is exposed to oxygen and moisture. This allows oxidation to begin, which effectively leads to the formation of rust. Over time, this corrosion can cause the coating to lift, blister or peel away from the surface, leaving more of the metal exposed.

If left untreated, cut edge corrosion can lead to:

• visible rust formation
• breakdown of the protective coating
• deterioration around sheet laps
• weakening of the metal sheet
• increased risk of water ingress
• issues being raised during dilapidations surveys.

Although it often begins as a localised issue, corrosion can gradually spread along the roof sheets if the underlying cause is not addressed.

Why does cut edge corrosion happen?

Cut edge corrosion develops because industrial roofs are exposed to some of the harshest conditions experienced by any part of a building.

The roof is constantly subjected to UV radiation, rain, wind, condensation, temperature movement and environmental pollutants. Over many years, these conditions gradually place stress on the original factory-applied coating.

Common causes include long-term UV exposure, moisture sitting at vulnerable edges, condensation around sheet laps, repeated weather cycles, ageing of the original coating system and pollutants in the surrounding environment.

Many industrial roofs installed 20–30 years ago are now reaching the stage where these issues are becoming visible during routine inspection. The roof may still be structurally sound, but the protective coating around vulnerable edges may no longer be performing as intended.

How to spot cut edge corrosion

Cut edge corrosion is often identified during roof inspections and dilapidation surveys, particularly around sheet laps and exposed edges.

Surveyors should look for reddish-brown staining or rust marks at the cut edges of the sheets. Early signs may appear as small spots or streaks, but these can indicate that the protective layer has already started to fail.

Other warning signs include peeling, blistering or flaking of the coating around sheet edges, corrosion visible along overlaps, staining around fixings, and signs of damp or water ingress inside the building.

Internal staining can be particularly important, as it may suggest that corrosion or coating failure has progressed far enough to affect roof performance. It may also become relevant during lease-end inspections or dilapidations assessments, where unresolved roof defects can create avoidable cost and liability for building occupiers or owners.

How cut edge corrosion progresses

Cut edge corrosion usually develops gradually.

It often begins with coating breakdown at the exposed edge of the steel sheet. Once the protective layer has failed, moisture and oxygen can reach the metal substrate. This leads to oxidation, which causes rust to form.

As rust expands, it can push against the remaining coating, causing further lifting, cracking or peeling. This exposes more of the steel surface and allows the corrosion to spread.

The typical progression is:

1. protective coating begins to break down
2. exposed steel becomes vulnerable to moisture and oxygen
3. rust starts to form
4. coating lifts or peels away
5. corrosion spreads along the sheet edge or lap.

This process can be accelerated by poor drainage, standing water, high humidity, industrial pollution or coastal environments.

Why early intervention matters

Early treatment is critical.

When cut edge corrosion is identified early, it can often be treated effectively as part of a planned refurbishment programme. This allows the roof to remain in service and can significantly extend its lifespan.

If corrosion is ignored, the damage becomes more extensive. Rust spreads along the laps, the coating continues to fail, and the steel sheets eventually deteriorate to the point where repair is no longer viable.

At that stage, the building owner may face more disruptive and expensive works, including sheet replacement or full roof replacement. For occupiers, landlords and managing agents, untreated cut edge corrosion can also become a significant dilapidations issue, particularly where deterioration has been allowed to progress over the course of a lease.

For surveyors, early identification and correct specification can help clients avoid escalating repair costs, reduce operational disruption, protect the long-term value of the building and manage potential cut edge corrosion dilapidations risks.

How cut edge corrosion is treated

Effective cut edge corrosion treatment begins with a proper inspection.

The condition of the roof should be assessed to understand the extent of the corrosion, the integrity of the existing sheets and whether refurbishment is appropriate. The correct treatment will depend on the level of deterioration and the overall condition of the roof.

A typical repair process includes inspection, cleaning, preparation, corrosion treatment and the application of a protective coating system.

Preparation is especially important. Loose material, failed coating and corrosion deposits need to be removed before treatment begins. The area must then be prepared in line with the system specification to ensure that the new coating can bond correctly and provide effective protection.

Once prepared, a suitable corrosion treatment and protective coating can be applied to encapsulate and protect the vulnerable edge, helping to prevent further deterioration.

How Giromax systems help

Giromax systems are designed to treat and protect vulnerable areas of industrial metal roofs, including cut edges, sheet laps and gutters.

The aim is to stop corrosion from progressing, restore protection to the exposed metal and extend the usable lifespan of the roof. This allows many building owners to refurbish rather than replace, reducing cost, disruption and waste.

This can be particularly valuable where surveyors are advising clients on maintenance planning, lease obligations or dilapidations. Addressing corrosion early can help demonstrate a proactive approach to roof condition, reducing the likelihood of more serious defects being identified later.

However, the performance of any refurbishment system depends on more than the product alone. Correct preparation, proper specification and trained application are all essential.

Giromax supports surveyors, contractors and property professionals with technical advice, specification guidance, CPD training and contractor support. This helps ensure that cut edge corrosion is assessed properly and treated using the right approach for the condition of the building.

Giromax® Edgecoat Pro – our newest high quality formulation, offers improved performance and protection for the unrivalled treatment of cut edge corrosion. Giromax® Edgecoat Pro is a highly durable solution with outstanding flexibility and elasticity, ideal for withstanding natural surface movements of the roof sheets.

Our Technical Services Managers are available to visit your premises, inspect your roof, and advise on the correct application of our cut edge corrosion treatment. Our advice goes beyond simply specifying the right product for your project, giving you confidence and providing technical service that is second to none.

We provide on-site training and technical guidance to contractors to ensure the work is carried out to a high standard. We will inspect each stage, from the preparation of the substrate to the coating application.

A manageable problem when treated early

Cut edge corrosion is common, but it is also manageable.

For many industrial roofs, early treatment can prevent further deterioration and extend the life of the building envelope for many years. The key is identifying the issue before it becomes more serious, specifying the correct refurbishment system and ensuring it is applied by trained contractors.

With the right technical approach, cut edge corrosion does not have to lead to full roof replacement. It can often be treated effectively as part of a planned refurbishment strategy, helping building owners, occupiers and surveyors manage roof condition, long-term costs and dilapidations risk.

For advice on cut edge corrosion treatment, speak to the Giromax technical team or attend one of our CPD sessions on industrial roof refurbishment and corrosion prevention.

At Giromax, we are the original innovators of cut edge corrosion treatments. Our roof coatings will help you protect the integrity and longevity of your industrial roofing system.

For technical guidance or application advice, please speak to the Giromax team or call 01455 388090.