What is cut edge corrosion?
Metal profile sheets are common on commercial buildings, but are susceptible to cut edge corrosion. Regular maintenance and timely repairs can prevent this turning into an extremely costly problem.
What is cut edge corrosion?
Cut edge corrosion is the damage and breakdown of material at the cut edge of a metal sheet. It usually refers to damage to metal profile sheets used in roofs at the roof edge, sheet overlaps or around fixings. Cut edge corrosion can also be found on metal canopies and cladding sheets, particularly at high level.
When metal sheets are made, they are coated with a protective film or paint or plastic that prevents water getting in contact with the metal. These coated sheets are later cut to size for use in commercial roofs, at which point an unprotected edge is exposed. This metal can then come into contact with water, salt and other pollutants, and start to corrode.
Why is cut edge corrosion a problem?
Cut edge corrosion is mostly a cosmetic issue when it first occurs, so why is it so problematic? It is because it can progress very rapidly, with rust and corrosion quickly spreading along the roof.
If cut edge corrosion is not treated and repaired quickly and effectively, the protective coating adjacent to it can start to peel off, exposing more of the roof. Left longer, the corrosion can affect the roof fixings, and can penetrate the entire depth of the roof sheet, leading to the material becoming brittle, holes forming and loss of structural integrity.
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Identifying cut edge corrosion on a condition survey
On a condition survey, building surveyors will be looking for signs of damage or corrosion throughout the metal profile roofing.
Cut edge corrosion can be difficult to spot from ground level, so surveyors make use of roof access, camera poles and drones to get a close look.
Particular attention is paid to the edges of the roof, sheet laps and fixing points. Surveyors will be looking out for signs of deterioration and rust, and for any areas where the protective coating is peeling, damaged or missing. They will also evaluation the condition of the metal, and whether or not it has become brittle.
Staining and discoloration around rooflights, valleys, and verges may indicate water damage, which often coincides with the onset or progression of corrosion in these areas. Similarly, damp patches and staining may be evident on the underside of the roof or on the walls of the property.
If cut edge corrosion is found, the surveyor will determine the extent of the problem. This allows them to provide advice on repairs and remedial works.
Repairing cut edge corrosion
If cut edge corrosion is found, it is important to act quickly to prevent further deterioration. If the corrosion is minor and limited to a small area, repair and recoating of the roof may be sufficient to prevent any more damage.
In this scenario, thorough cleaning and preparation should also be included in the budget costs; this preparation is crucial to make sure the coating will stick properly to the metal surface. Full coating, including the ends of laps, can effectively treat the early stages of cut edge corrosion and allow metal sheets to stay intact and in repair for 15–20 years, provided they are well maintained.
In cases where corrosion has spread and caused significant damage, replacement of fixings, individual sheets or even entire roofs may be necessary. In addition, if the corrosion is widespread and the cost of repeated repairs over its remaining lifetime is greater than 50% of the cost of a new roof, replacement should be considered. If multiple repair attempts have failed and issues keep coming back, investing in a new roof is often more economical long-term. However, repair is still viable if the corrosion to sheets is only surface-level on the sheets.
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