Cut edge corrosion on commercial and industrial roofs

Cut edge corrosion is one of the most common, and most underdiagnosed problems affecting commercial and industrial metal roofing in the UK, with many building owners being completely unaware their property is affected.

What is cut edge corrosion?

When metal roof cladding is manufactured, corrugated sheets are coated in a protective plastic layer that prevents the underlying metal from corroding and improves its appearance. The sheets are then cut to size in a factory, leaving the cut edges with no protective coating and an exposed line of metal.

Once the sheets are installed on a roof, those uncoated cut edges are exposed to oxygen, moisture, and atmospheric pollutants. Over time, the original factory coating begins to peel back from the uncovered edges, causing the exposed metal to oxidise and corrode.

This process is known as cut edge corrosion.

It most commonly occurs at sheet overlaps, eave edges, and areas where metal guttering is poorly fitted or blocked, allowing moisture to gather against exposed metal surfaces.

What causes cut edge corrosion?

Cut edge corrosion occurs when cut edges of metal sheets are left with no protective coating, which makes them vulnerable to weathering and oxidation immediately after they’re installed.

Normal weathering can cause the problem at sheet overlaps and eaves, where capillary water is held in lap joints, meaning it’s constantly in contact with the unprotected edge.

Changes to temperature can also speed the problem up because the metal sheets expand and contract as the weather changes. This constant movement causes the protective coating to delaminate from the cladding, creating more exposed metal that corrodes.

Exposing metal roof sheets to oxygen, water and natural pollutants in the air can also speed up cut edge corrosion, while poorly fitted and debris-blocked guttering can create damp conditions that get through exposed metal edges, which spread to other parts of the building.

How to spot cut edge corrosion

Early detection is important because cut edge corrosion gets worse the longer it’s left.

You should schedule regular commercial roof maintenance with qualified industrial roofing contractors who can inspect both the interior and exterior of your roof safely.

When carrying out your own visual checks, look for things like flaking or warped metal edges, visible rust or discoloration along sheet edges, corrosion blisters forming around roof joints and overlaps and peeling or lifting of the original protective layer at eave edges.

If you spot any of these signs, contact qualified industrial roofing contractors. Delaying treatment allows the corrosion to spread and increases the cost of repair.

Cut edge corrosion issues

If left untreated, cut edge corrosion damage follows a fairly predictable pattern that gets worse the longer it’s left.

To start with, the protective coating on your roof sheets continues to peel back, exposing more unprotected metal roof.

Water can then penetrate the exposed metal, causing it to rust, which then eats into the cladding and causing it to become brittle.

When this happens, the cladding can no longer keep water out so leaks develop.

In more advanced cases, cut edge corrosion destroys the weather-sealed lap joint and gutter overhang entirely.

At this stage, the structural integrity of your roof is compromised and if water is able to get through the roof and into the interior of your building you then risk more damage and safety risks.

So what started as a straightforward surface treatment becomes a full commercial roof repair or replacement.

For buildings with asbestos-containing cladding, the situation is more complicated.

Removing and disposing of asbestos sheets is a difficult and heavily regulated task. Starting cut edge corrosion treatment early, rather than getting to the point where you have to remove roof sheets can be even more important in these cases.

How to treat cut edge corrosion?

How you treat cut edge corrosion depends on how far the corrosion has progressed.

If you find it early, the roof laps can be treated with a low modulus silicone system. This approach is effective at sealing the exposed edges, halting the spread of corrosion, and extending the lifespan of the roof sheeting by 15 years at least.

Where cut edge corrosion is more advanced, the treatment process follows these stages:

•   Thorough cleaning of the affected cladding to remove grime, debris, and contaminants.

•   Removal of loose paint, rust, and any corroded areas, with the extent of removal depending on the severity of the corrosion.

•   Application of a high-quality weatherproof sealant to the prepared surfaces.

•   Application of a metal cladding coating for ongoing protection against the elements.

In cases where cladding sheets are severely corroded and beyond repair, individual roof sheets may need to be replaced before the coating is applied. However, this is significantly less disruptive and expensive than a full roof replacement, which is the likely outcome if corrosion is left to deteriorate over many years.

How NWIR can help with cut edge corrosion

At NWIR, we carry out thorough assessments of commercial and industrial cladding and advise on the most appropriate way to treat cut edge corrosion before any repair work begins.

We cover all of the UK’s major cities and are qualified and trained to work safely at height.

We advise scheduling regular commercial roof maintenance so that issues like cut edge corrosion are identified and resolved before they become costly. Regular inspections also allow us to check for a range of other roofing issues simultaneously, helping you to extend the life of your roofing system and avoid unplanned repairs.

If you suspect your roof may be affected by cut edge corrosion, or you would like to arrange a regular maintenance programme, contact our team today.

You can either give us a call on 0800 046 1500, or send us a message using our online contact form and we’ll get back to you as soon as possible.