Weathering Steel Planters and Facade Panels: Detailing Against Patina Staining

Weathering steel has become a favourite of landscape architects and facade designers, and most complaints that follow it are not about the steel at all. The panel weathers exactly as intended. What damages the project is the rust-coloured water running off it during the first two or three years, staining whatever sits underneath.

Where the staining actually comes from.

Fresh weathering steel loses a noticeable amount of oxide in every rain cycle until the patina seals. The runoff is iron oxide in water: it marks concrete, paving, glass, timber decking and light stone almost permanently. Once the patina is mature the runoff drops sharply, but by then the lawn beside the planter and the render under the facade may already carry brown streaks.

Planter details that work.

A corten planter should never drain directly onto a lawn or deck. Route the drainage through a pipe to a soakaway or drain, keep the planter foot on plinths or gravel so standing water cannot sit against the base, and never let irrigation spray the steel face. Inside, a waterproof liner keeps wet soil off the steel wall, because permanently damp soil contact corrodes far faster than rain ever will.

Facade details that work.

What to tell the client before delivery.

The honest specification says three things: runoff will occur and will decrease with time; horizontal surfaces weather slower and should be detailed away from sight lines; and the steel must not touch absorbent materials. Projects that accept this need nothing beyond occasional cleaning of nearby surfaces. Projects that expect a dry, colour-stable surface from day one should be quoted in coated steel instead.

We supply weathering steel plates and coils for planters, facades and landscape work in S355J0WP, S355J2WP, A588 and 09CuPCrNi-A. Send us your thickness list for an offer.