It is common for cast iron for outdoor use, such as footscrapers and garden urns, to become rusty and flaky at first, but after a few months the rusting stops. After that, the cast iron takes on a slightly smoother brownish-black surface. This can take different lengths of time and depends a lot on the local climate.
The newly formed surface layer prevents the iron from rusting further, but to maintain the surface, you can use boiled linseed oil. In our article, “Let the iron rust,” you will find even more information about the process of rust.
