What is Corten steel?

If you’ve just taken delivery of a Corten planter and it looks nothing like the photographs, this page is for you. Nothing has gone wrong.

It arrives the wrong colour

Corten, properly called weathering steel, leaves our workshop raw. Flat, blue-grey, faintly industrial. People do occasionally ring us about this on the day it arrives.

Leave it outside. Over roughly four months the surface oxidises into the deep orange-brown you were expecting. Wet spells and dry spells alternating are what drive it, so a British autumn does the job nicely.

You don’t have to do anything

No treatment, no sealant, no oil, no help of any kind. Rain and air do all of it. Anything you paint or seal it with will actively prevent the process.

Why the rust doesn’t keep going

This is the part that surprises people. On ordinary steel, rust is porous. Water gets underneath it, and the corrosion keeps eating inward until there’s nothing left.

Corten has copper, chromium and nickel in the alloy. Those cause the oxide layer to form tight and stable rather than flaky, and once it’s formed it seals the metal underneath from further moisture. The reaction slows dramatically and effectively stops. What you end up with is a protective skin, not an ongoing problem.

It’s the same steel used for bridges and outdoor sculpture, chosen precisely because it looks after itself for decades without painting.

The one mistake worth avoiding

While it’s weathering, the run-off carries rust particles. On pale limestone, new decking, block paving or render, that staining is difficult to remove and sometimes permanent.

For the first few months, stand it on soil, gravel, grass or dark paving. Once the patina has stabilised the run-off largely stops, and you can move it wherever you like.

How it ages after that

The colour deepens and evens out over the first year or two, then settles. It’ll darken in wet weather and lighten as it dries. That shift is normal and part of the appeal. No two pieces weather identically, which is rather the point.

Ours carry a three year guarantee, but a Corten planter that’s been left alone should outlast the garden around it.

Would painted steel suit you better?

If you want a colour that stays put, or you’re placing it somewhere the staining would be a problem, our painted range is galvanised underneath and etch primed before painting. Anthracite grey, black or white as standard, any RAL shade on request.

Not sure which way to go? Call us on 020 8539 0611 and describe where it’s going. We’ll tell you straight.