Weathering steel forms a stable, rusty appearance after about six months of exposure to weather, though the time required to obtain this effect can be shortened to as little as two hours with surface treatments. The unique nature of Corten resistant steel is that it resists corrosion, but forms a complete outer layer of rust that protects the underlying steel from damage.
It is important to note that the steel must go through wet and dry cycles in order for the weathering effect to take place. Corten steel will not develop its protective layer if it is kept underwater or in muddy conditions. Ocean water can also corrode the steel before it can become weathered, so it is not recommended for use on or near the shore.