Cladding & Roof Coatings

What is Cut Edge Corrosion? Causes, Signs & Professional Repair

Q: How common is cut edge corrosion on commercial buildings?

Cut edge corrosion is extremely common. The MCRMA (Metal Cladding and Roofing Manufacturers Association) lists it as one of the most prevalent maintenance issues affecting steel-profiled cladding, particularly on buildings over 10 years old that have not been professionally inspected. The condition is so common because every steel or aluminium cladding sheet has cut edges, and very few factory coating systems adequately protect the cut profile. It is particularly prevalent on buildings over 10 years old that have not had their cladding professionally inspected or treated.

Q: Where does cut edge corrosion typically start?

Cut edge corrosion typically begins at the sheet overlapping edges, at the eaves, and at horizontal laps, the points where sheets overlap one another and water is most likely to penetrate and sit. Horizontal laps are particularly vulnerable because water collecting in the overlap channel has a direct path to the uncoated cut edge. From these starting points, capillary water action draws the moisture beneath the factory coating and spreads the corrosion across a wider area than is visible from the surface.

Q: What are the signs of cut edge corrosion?

Early signs include discolouration or staining at sheet edges and overlaps, small blisters or bubbles in the surface coating, and a chalky or flaking appearance at the edges. As the condition progresses, the coating peels back from the edges in strips, rust staining becomes visible on adjacent surfaces, and in advanced cases the underlying metal becomes perforated or structurally weakened. Many building owners only notice cut edge corrosion once it has progressed significantly, which is why periodic professional inspection is recommended.

Q: Can cut edge corrosion be repaired without replacing the cladding?

In the majority of cases, yes, cut edge corrosion can be professionally treated and recoated without full cladding replacement. The correct process involves mechanical removal of all loose and flaking coating, treating and neutralising any active rust, feathering the edges of remaining sound coating, applying a purpose-formulated cut edge corrosion treatment system, and finishing with a durable weatherproof topcoat. Early intervention is essential, once sheets become perforated or the substrate is structurally compromised, replacement may be the only viable option.

Q: How long does a cut edge corrosion treatment last?

A professionally applied cut edge corrosion treatment system applied to properly prepared substrate, using a quality coating formulated for PVC-coated metal cladding, can be expected to provide 10–15 years of protection before re-treatment is required. Longevity depends on the building's exposure to UV, moisture and atmospheric pollutants, and on the quality of preparation, in particular, whether all loose coating and active rust was fully removed before the treatment system was applied.

Cut edge corrosion is the most common form of metal cladding deterioration on UK commercial buildings, and one of the most frequently overlooked. This guide explains what causes it, how to identify it early, and the correct professional treatment process that restores protection without replacing the sheets.

Anthony Jones, Vanda Coatings Updated February 2026 9 min read Cut Edge Corrosion Cladding Technical Guide

Corrugated steel and aluminium profiled sheets have become a standard choice for commercial building envelopes, cladding the walls and roofs of warehouses, industrial units, retail parks, distribution centres, and even hospitals and schools. Their durability and low installation cost make them practical. But they share a common vulnerability that the construction industry has never fully resolved at the manufacturing stage: the cut edge.

When sheet metal cladding is produced, the flat or profiled sheet receives its protective factory coating, typically a plastisol, PVF2 (PVDF), or polyester system, before being cut to the required dimensions. This means the final cut edge of every sheet is bare, uncoated metal. There is no protective layer on it at all. And it is this exposed edge, often hidden within an overlap or at the eaves, that begins to corrode from the moment it is exposed to the UK atmosphere.

The problem is so widespread that the MCRMA (Metal Cladding and Roofing Manufacturers Association) identifies cut edge corrosion as one of the most common maintenance issues affecting steel-profiled cladding in the UK, particularly on buildings over 10 years old. Much of it goes undetected because the damage begins in hidden or hard-to-inspect locations before becoming visible on the surface.

What exactly is cut edge corrosion?

Cut edge corrosion is the oxidation and progressive deterioration that occurs at the raw, unprotected edges of metal cladding sheets. It is not simply surface rust. The mechanism involves the corrosion beginning at the exposed metal edge, then advancing beneath the adjacent factory coating through capillary water action, the same process that draws water up between closely overlapping surfaces.

Water infiltrates the tiny gap between the sheet edge and the overlapping panel above it, sits in contact with the uncoated substrate, and begins the electrochemical oxidation process that produces rust on steel or white corrosion on aluminium. As the rust expands in volume, it undercuts and lifts the adjacent factory coating, a process called delamination, extending the unprotected area and allowing further water ingress in a self-reinforcing cycle.

Left untreated, cut edge corrosion progresses from a localised edge defect to widespread coating failure across large areas of sheeting, eventually perforating the substrate and compromising the cladding system's structural integrity.

No. 1

most common maintenance issue on commercial steel cladding, per MCRMA guidance

10–15

years protection expected from a professionally applied treatment system

80%

cost saving of professional re-treatment versus full cladding replacement

steps in the correct professional cut edge corrosion treatment process

What causes cut edge corrosion?

Several mechanisms contribute to cut edge corrosion. The primary cause is always the same, uncoated substrate at the sheet edges, but secondary factors accelerate the rate of deterioration.

Uncoated cut edges

The fundamental cause. Metal sheets are coated during manufacture, then cut to size. The cut profile is bare metal with no protective layer, factory coatings cannot be applied economically to cut edges in production. Every overlap, every trimmed edge is a potential corrosion initiation site. This is an inherent characteristic of profiled metal cladding systems, not a manufacturing defect.

Capillary water action

Where sheets overlap, water is drawn by capillary action into the tight gap between the panels, even against gravity. This capillary channel delivers water directly to the cut edge and holds it in contact with the unprotected substrate for extended periods. Horizontal laps are particularly vulnerable because the geometry creates a near-horizontal channel that retains water rather than allowing it to drain freely.

Thermal movement

Metal expands when warm and contracts when cool. Profiled metal cladding sheets cycle through significant thermal movement across the seasons and between day and night. This constant dimensional change stresses the bond between the factory coating and the substrate, particularly at edges and overlaps, causing micro-cracking that admits water. Over years, the combined effect of thermal fatigue and moisture infiltration accelerates delamination.

UV degradation of factory coatings

Factory coatings, particularly older plastisol systems, become increasingly brittle as UV radiation degrades the polymer binder over time. As the coating loses flexibility, it is less able to accommodate the thermal movement of the underlying metal, leading to cracking and delamination independent of the cut edge condition. UV-degraded coatings also lose their barrier properties, admitting moisture more readily across the full sheet surface.

Signs of cut edge corrosion

Identifying cut edge corrosion early, before it has spread significantly beyond the edges, is the key to cost effective treatment. These are the signs to look for, roughly in order of progression from early to advanced:

Early-stage indicators

Slight discolouration or staining at sheet overlaps and eave junctions
Small blisters or bubbles in the factory coating at or near overlap positions
A chalky or powdery surface texture on the factory coating (indicating UV degradation of the binder)
Orange-brown staining tracking downward from overlap positions on the sheet face

Mid-stage indicators

Visible peeling or lifting of the factory coating at and around the overlap edges
Rust staining on adjacent surfaces or at the base of the cladding system
Gaps appearing at the cut edge where the coating has delaminated away from the metal
A pronounced line of coating failure running parallel to and near the sheet edge

Advanced-stage indicators

Large sections of the factory coating peeling away from the sheet face
Visible active rust or pitting across significant areas of the substrate
Perforation of the steel substrate in the worst-affected areas
Water ingress through the cladding causing internal staining or dampness

Do not delay inspection if you see blistering at overlaps. Once cut edge corrosion has progressed to the point where the substrate is perforated, treatment options are limited. At that stage, the affected sheets will need to be replaced rather than recoated, significantly increasing cost. Early identification and treatment is almost always the most economical course of action. If you are uncertain whether blistering you can see constitutes early-stage cut edge corrosion, commission a professional inspection.

Damage progression and treatment options

The appropriate treatment depends on the stage of deterioration. Understanding where your cladding sits on this scale determines whether professional treatment is viable or whether sheet replacement is necessary.

Stage	Visual signs	Substrate condition	Treatment option	Urgency
Stage 1. Early	Edge staining, minor blisters at overlaps	Sound, no substrate loss	Professional cut edge treatment system	Plan within 12 months
Stage 2. Moderate	Coating peeling at edges, rust staining visible	Surface corrosion but no perforation	Professional treatment, more preparation required	Treat within 6 months
Stage 3. Advanced	Widespread delamination, significant rust areas	Active rust, possible pitting beginning	Treatment viable but complex; sheet edges may need cutting back	Treat urgently
Stage 4. Critical	Large-scale coating loss, perforation visible	Perforated or structurally weakened	Affected sheets must be replaced before recoating	Immediate action

The professional cut edge corrosion treatment process

Professional treatment of cut edge corrosion is a systematic eight-stage process. Each stage is essential, skipping preparation steps produces a surface that looks treated but retains moisture and fails within a few years. The quality of the work is determined as much by what happens before the coating is applied as by the coating itself.

Inspection and assessment

A thorough inspection of all cladding surfaces, including a close examination of all overlaps, eaves, gutters, and fixings, establishes the extent and severity of cut edge corrosion. This determines the quantity of treatment product required, identifies any sheets that need replacement before treatment can proceed, and informs the programme of works. A written report with photographic documentation should accompany any professional inspection.

Replace severely corroded sheets

Sheets that are perforated, structurally weakened, or where corrosion has progressed to the point that treatment cannot produce a sound, durable finish must be replaced at this stage. Attempting to treat perforated sheets wastes material and produces a result that will fail rapidly. New replacement sheets should be treated as part of the same programme.

Pressure clean

Thorough pressure washing of all cladding surfaces removes moss, algae, lichen, atmospheric dirt, and loose debris. Clean surfaces are essential for adhesion of all subsequent materials. Moss and algae in particular must be removed completely, they retain moisture against the surface and can continue growing beneath a new coating if not fully eliminated. A biocidal wash is applied after pressure cleaning and allowed to dwell before rinsing.

Mechanical removal of flaking coating and rust

All areas of loose, flaking, and delaminating factory coating are mechanically removed using wire brushing, hand tools, or angle grinders. Active rust on exposed steel is mechanically abraded back to sound metal. This is the most labour-intensive element of the process, cutting corners here is the most common cause of premature treatment failure. Any rust that remains beneath a new coating will continue to spread, undermining the new system from below.

Feather the edges of remaining sound coating

Where sound factory coating remains adjacent to areas of loss, the edge is feathered by sanding or abrading to eliminate any abrupt step between the remaining coating and the exposed substrate. Ridges and sharp edges at coating boundaries create points of stress concentration in any new coating applied over them, leading to premature cracking and water ingress. Feathering ensures a smooth, continuous transition across the treated area.

Degrease and clean

All surfaces are thoroughly cleaned with an appropriate degreasing agent before any coating is applied. Even on apparently clean surfaces, hand contamination from preparation work, residual moss and algae residue, and atmospheric deposits can impair adhesion. Degreasing is a non-negotiable step regardless of how clean the surface appears, a degreased surface that looks no different to the eye bonds far better than one that has not been treated.

Seal overlaps and joints

All gaps between overlapping sheet edges, at eaves, around fixings, and at joints are sealed using an appropriate grade of sealant before the treatment coating is applied. Sealing eliminates the capillary pathways that originally admitted water to the cut edges. It is particularly important at horizontal laps where the geometry creates a persistent water trap. The sealant must be compatible with the subsequent coating system and applied to a clean, dry surface.

Apply cut edge treatment system and weatherproof topcoat

A purpose-formulated cut edge corrosion treatment, typically a high-build, flexible sealer, is applied to all cut edges, overlaps, and any areas of exposed substrate. This is followed by a weatherproof topcoat compatible with the original factory coating system. The completed treatment must achieve the specified dry film thickness across all treated areas. Colour-matched topcoats can restore a consistent appearance to cladding where the factory colour has faded unevenly.

At Vanda Coatings, every cut edge corrosion treatment project begins with a free professional site inspection and written assessment. We specify only coating systems formulated for PVC-coated metal cladding and applied by operatives experienced in working at height on commercial roofing and cladding systems. Our treatment programmes are documented with pre- and post-treatment photography and include a written specification of all materials applied.

Cut edge corrosion and gutters

Metal guttering associated with cladded buildings is susceptible to a related but distinct form of deterioration. Gutters that are blocked with debris or incorrectly fall-graded cause water to sit in contact with cut edges of the sheets above the gutter line for extended periods, accelerating cut edge corrosion in the eaves region far beyond what would occur with a free-draining gutter. The gutter itself, particularly older galvanised or pressed steel gutters, can also fail through corrosion, allowing water to penetrate the building structure and cause dampness that further accelerates cut edge corrosion on adjacent cladding.

It is standard practice for Vanda Coatings to assess gutter condition as part of any cladding treatment survey. Gutters should be cleared and any blockages or fall defects corrected before the cladding treatment is carried out, the investment in treatment is wasted if water continues to be directed to the eaves edge in greater-than-designed quantities.

How to prevent cut edge corrosion recurring

Once a professional cut edge corrosion treatment has been applied, a maintenance programme extends the service life of the treatment and protects the investment:

Keep gutters and downpipes clear, inspect and clear at least twice annually, in spring and autumn
Inspect cladding overlaps and eaves annually, looking for early signs of blistering or staining
Touch in any minor damage to the treatment topcoat promptly, small areas of damage are cheap to rectify; ignored, they become large ones
Trim back any vegetation growing against or over the cladding, moss growth retains moisture and accelerates deterioration
Commission a professional inspection every 3–5 years to assess coating condition and identify any areas requiring early intervention

Frequently asked questions

Q What is cut edge corrosion?

Cut edge corrosion is the deterioration that occurs at the raw, unprotected edges of metal cladding sheets. During manufacture, sheets are cut to size after their protective factory coating has been applied, leaving bare metal at every cut edge. When exposed to moisture, these uncoated edges oxidise and corrode. The corrosion spreads beneath the adjacent factory coating through capillary water action, causing progressive delamination that extends well beyond the original cut edge.

Q How common is cut edge corrosion on commercial buildings?

Very common. The MCRMA (Metal Cladding and Roofing Manufacturers Association) identifies it as one of the most prevalent maintenance issues on commercial steel-profiled cladding, particularly buildings over 10 years old. Every cladding sheet has cut edges, and few factory coating systems adequately protect the cut profile. The condition is particularly prevalent on buildings over 10 years old that have not had their cladding professionally inspected.

Q Where does cut edge corrosion typically start?

Cut edge corrosion typically starts at sheet overlapping edges, at the eaves, and at horizontal laps, where sheets overlap one another and water is most likely to penetrate and sit. Horizontal laps are particularly vulnerable because the overlap geometry creates a channel that retains water in direct contact with the cut edge. From these initiation points, capillary action draws moisture beneath the factory coating, spreading the corrosion into areas well away from the visible edge.

Q What are the early signs of cut edge corrosion?

Early signs include discolouration or orange staining at sheet edges and overlaps, small blisters or bubbles in the surface coating near overlap positions, and a chalky surface texture indicating UV degradation of the coating binder. At this stage the underlying metal is still sound and treatment is straightforward. As the condition progresses, the coating begins to peel back from the edges in strips and rust staining becomes visible on adjacent surfaces.

Q Can cut edge corrosion be repaired without replacing the cladding?

In the majority of cases, yes. Professional treatment, involving mechanical removal of all loose coating and active rust, sealing of overlaps and gaps, and application of a purpose-formulated cut edge treatment system and weatherproof topcoat, can restore and extend the service life of cladding without the cost and disruption of replacement. Early intervention is essential: once sheets become perforated, replacement of those sheets becomes necessary before recoating can take place.

Q How long does a cut edge corrosion treatment last?

A professionally applied treatment using a quality coating system formulated for metal cladding, on a properly prepared substrate, can be expected to provide 10–15 years of protection before re-treatment is required. Longevity depends on the building's UV and moisture exposure and on the quality of preparation, thorough removal of all loose coating and active rust is the single most important factor in treatment durability.

Anthony Jones

Director, Vanda Coatings, 29 years experience

Anthony has been inspecting and treating cut edge corrosion on commercial cladding systems across the UK since the late 1990s. The condition is one of the most consistently under-appreciated maintenance issues in commercial property, by the time it becomes visible from ground level, it has almost always been developing for years. Early inspection and treatment is the single most cost effective decision a building owner can make regarding their cladding.