What is Cut Edge Corrosion?

Years ago, corrugated steel or aluminium sheets merely cladded barns and sheds, now this ‘crinkly tin’ as architects often call it, may be used on a range of commercial building elevations or roofs. Warehouses, retail units, hospitals and even art galleries use cladding as a protective and aesthetic layer. It is estimated that 60% of cladding has cut edge corrosion, but many owners of commercial properties are not aware their business suffers from this problem and they often don’t even know what cut edge corrosion is.

When metal cladding is manufactured, the corrugated sheets are coated in plastic such as Plastisol. This coating prevents the underlying metal from being corroded by the elements and also improves its appearance. After the cladding is cut to size in a factory before being attached to the roof or elevation of a commercial building, the cut edge isn’t coated. A steel edge exposed to oxygen is prone to corrosion which is exacerbated by water and pollutants. Consequently, the factory coating can peel off from these edges.

Any metal edge may be vulnerable, so cut edge corrosion is usually found on the edges of sheets where they overlap one another and at the eaves. The horizontal laps are particularly vulnerable to this type of deterioration. Even though cut edge corrosion usually begins around edges it gathers speed through capillary water action and can spread.

Metal guttering can also suffer from cut edge corrosion and may fail in other ways. If gutters are ill fitted or clogged up then damp can penetrate a commercial property causing structural weaknesses as well as further cut edge corrosion on other panels of cladding.

Another cause is the changing shape of the metal substrate. Metal can expand with rises in temperature and contract when cool. As the cladding expands, the factory coating can lift which exposes the underlying substrate. Consequently, the elements take their toll and eventually more and more of the coating can delaminate.

Delamination and coating failure can occur anywhere on cladding not just at the cut edges and the causes of deterioration vary. Telltale signs are discolouration or when cracks and blisters can be seen on a top layer. Harsh UV rays lead to fading and can make cladding coating hard and brittle. The lack of flexibility hinders the expansion of the underlying metal leading to delamination.

As time goes on, the original coating peels away from the metal surface. This allows water to penetrate the substrate leading to rust. Without the protection of an intact coating, rust can eat away at the cladding. This makes it brittle and leads to leaks which can then affect the integrity of the building in many ways. Sometimes, the metal cladding can become perforated which can be very expensive to repair, so the earlier cut edge corrosion is treated, the better.

Repairing cut edge corrosion will protect cladding from the elements and pollution as well as reducing the peel back of the coating. It will provide a tight seal on the horizontal laps, lap joints and the edges of cladding. If done by a professional company, repairs will improve how a building looks as well as protecting it structurally.

How to Repair Cut Edge Corrosion:

1. Inspect the cladding to estimate the extent of damage and the amount of products needed for repairing and re-coating the cladding.
2. Any badly corroded metal cladding sheets may need replacing.
3. Thoroughly clean off any moss, algae and grime from the surface. A high pressure water jet may be necessary for this.
4. Mechanically remove or brush off flaking paint and rust depending on the severity of the problem.
5. Feather the edges of the original peeling coating and delaminated areas, so there are no ridges when the new layer is applied.
6. Clean the cladding again using a degreasing agent otherwise grime will prevent new coatings from sticking to surface.
7. Fill in any large gaps between overlapping cladding panels using a gun to apply the sealant.
8. It is crucial to re-spray cladding (and if necessary, gutters and any metal fixings) with an appropriate top coat manufactured especially for PVC coated metal cladding. A specially designed new coating will have corrosion resistant properties and is available in any colour.

Treating cut edge corrosion will prolong the life of the cladding and therefore the whole building, but re-painting cladding isn’t just necessary to repair cut edge corrosion, a new coat of paint may be required simply for a change in colour or to counteract fading for example.