What is Cut Edge Corrosion?
Cut edge corrosion is a common issue that affects aged metal profile roofs, predominantly around the sheet laps and sheet end areas. During the manufacturing process, a layer of coating is applied to galvanised steel sheets to colour and provide extra protection. The coating varies by product, usually PVC, Polyester and PVDF are used for standard applications, for more corrosive environments specialist brand coatings such as TATA steel HPS 200 is often used in marine or coastal locations.
Once coated, the galvanised steel sheet is then rolled into large coils, before being sent to be cut and profiled to the tailored roof system specification. However, where the sheets have been cut it also creates an exposed untreated metal edge. Lacking a protective layer of coating, this edge is particularly vulnerable to corrosion caused by weathering.
Over time this corrosion can cause the protective coating to de-laminate from the underlying metal and begins to peel back from the sheet edge. This in turn exposes more of the metal to the effects of weathering, further exacerbating the problem. If left untreated this exposure will cause the metal to corrode and eventually perforate.
On any metal roof, coating peel back is inevitable when left neglected. Early detection and treatment of cut edge corrosion is vital to stop continuing coating peel back from the sheet edge. Left untreated, the damage will get progressively worse until a complete replacement of the roof sheets will be your only option for repair.
What to Look Out For?
As the name suggests cut edge corrosion is normally found at the edge of sheets. Look out for rusting or the protective coating peeling along any edge. The bottom of eaves are particularly vulnerable, as are any horizontal laps between sheets. Fixing points are another area that needs close attention. Washers may have degraded allowing water ingress, which will cause corrosion.