Corrugated metal sheets have a Plastisol coating this is to ensure longevity and to stop weathering of sheets.
Over time even machine cut edges are prone to plastisol peeling, causing rust and corrosion. If the rust is left to progress past the fixing lines major roof work will need to be undertaken. If caught soon enough Seamsil Lap Edge Protection could save you from a complete new roof!
NLS is an approved supplier and installer for Seamsil Lap Edge Protection.