Leaving your urban outdoor furniture uncovered exposes it to the elements, and rust can form surprisingly quickly. The exact timeline isn't a single answer; it depends heavily on the metal type, your local climate, and air quality.
For unprotected iron or steel, the first signs of surface rust can appear within a few weeks to a year, especially in humid, coastal, or industrial areas with high salinity or pollution. These conditions accelerate corrosion. A powder-coated finish provides a strong barrier, but once this coating is scratched or chipped, the underlying metal becomes vulnerable.
Aluminum and stainless steel are highly rust-resistant. Aluminum forms a protective oxide layer, while stainless steel contains chromium for protection. They can last for many years without significant rust, though stainless steel can still stain. To significantly slow down rust, use protective covers, apply automotive wax, and keep furniture clean and dry. Regular maintenance is the key to longevity.