Cor-Ten is a weathering steel; after being exposed to the elements, the top layer becomes a protective rust that never needs painting. Although Cor-Ten is otherwise quite corrosion resistant, it is not completely immune to corrosion. If used near the sea in salty air or if exposed to standing water, it will continue to corrode beyond the initial rusting phase, and thus is not recommended for use under such conditions. Cor-Ten steel is the trademarked but common name for steel in which various alloys are added to create a layer of rust on its surface. Also called weathering steel, this oxidized surface eliminates the need for paint or some other weatherproofing treatment.