The existing factory colour has gone dull and rubs off as a powder when you touch it. I'd like to recoat rather than replace but I'm worried about what the new coating will actually be sticking to.
Do not coat straight over it. That chalky powder is degraded coating, and anything you apply on top will only bond to the loose layer, not the metal, so it will lift. A coating is only ever as good as the preparation and the surface it goes onto. The surface needs to be thoroughly cleaned back to a sound, stable base, typically by washing down and abrading to remove all chalk, dirt and any loose or flaking material, plus dealing with rust spots and treating bare steel. Exact preparation depends on the substrate and the system being used, so it is worth confirming the spec for your roof. Happy to look at it and set out the right build-up if you get in touch.
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