I'm thinking of repainting the metal parapet on the balcony, paint has already mostly come off, or it is peeling off (and the metal is also starting to rust). Every description starts with scraping off rust and old paint which is fair enough.
Several years ago, I had repainted a smaller, similar parapet, and to get all the paint off was a long and painful process, because most of it was still stuck to the metal.
What I'm not sure about: are you supposed to get all the old paint off, or only the part which is peeling away, and hence is easy to remove?
(In other words: can you partly remove the old paint, and then paint over the remaining patches, which are still stuck to the metal? If yes, what are the disadvantages of doing so?)
Similar question, but about wooden frames. (Maybe answer is different for metal?)