What Is Weathering Steel? Everything You Need to Know

If you've spent any time on our website, you've probably noticed we mention weathering steel a lot. It's the material we make almost everything from — signs, garden art, letterboxes, tree spikes, memorials — and for good reason. But what actually is it, and why does it suit outdoor use so well? Here's everything worth knowing.

Weathering steel is a steel alloy specifically designed to rust — on purpose. When it's exposed to the weather, the surface forms a dense, stable oxide layer that acts as a natural barrier, stopping the corrosion from going any deeper. Unlike regular steel, which rusts through and deteriorates over time, weathering steel rusts on the surface only, and that layer continues to regenerate and strengthen over years of outdoor exposure.

The result is a material that is genuinely low-maintenance, built to last outdoors for years, and develops a beautiful warm, rustic patina that only improves with age.

You might have heard of it by its trademark name COR-TEN, or simply Corten. Here at Custom Steel Appeal, we use REDCOR — the Australian-made equivalent produced by Bluescope. We choose REDCOR specifically because it's made here in Australia and is suited to Australian conditions, including our UV levels, temperature extremes, and variable rainfall.

As all of our pieces are made to order and we aim to get them to you as quickly as possible, they arrive in their raw form — the traditional flat grey of unweathered steel. This surprises some people who are expecting the rusty patina they've seen in product photos, so it's worth knowing what to expect.

The good news is that the patina develops relatively quickly once the piece is outside. Most pieces start looking noticeably rusty within a couple of weeks. Full weathering — where the piece is properly sealed and stops releasing any rust residue — takes around 3–6 months depending on your climate and how much moisture the piece is exposed to.

A few things to keep in mind in the early weeks:

• Avoid placing a freshly delivered piece on white surfaces or light-coloured pavers until it's fully weathered, as rust runoff can stain. A natural surface like timber or bare ground is ideal while it's settling in.
• Metal left in direct sunlight for extended periods can get quite hot to the touch — worth considering when deciding on a permanent placement spot, especially if you have small children or pets.

If you'd like to speed things up, here's what we've found works best through our own experimenting:

💧 Water it regularly
Regular tap water is all you need. During dry periods, water your piece at least once a day — we tend to water twice daily in the height of summer, once in the morning and again at sunset. In spring and autumn, even dewy mornings will help kick things along.

💦 Keep it flat while it weathers
We've noticed a significant difference in weathering speed between pieces left flat versus pieces standing upright. Flat pieces allow water to sit on the surface longer rather than running straight off, which accelerates the process. If you notice water pooling to one side, rotate the piece weekly for a more even finish.

🌥️ A sheltered spot helps
If the water can sit on the surface a little longer before evaporating, the weathering speeds up. A spot that's sheltered from direct sun — a shaded corner, under a verandah — works well for the first few weeks. That said, we know this isn't always practical, and the piece will weather perfectly well in full sun too, just a little more slowly.

Completely fine. Simply placing your piece outside and leaving it to its own devices will achieve the same result — it'll just take a little longer to fully develop its patina. Weathering steel is designed to work with the weather, not against it.

No. Weathering steel rusts on purpose, but only on the surface — that's the protective layer doing its job. It won't rust through.

Yes, for most Australian conditions. The one exception worth noting is extreme coastal environments — within approximately 500m of breaking surf — where very high salt air can interfere with how the patina forms. If you're in a directly coastal location, get in touch and we can talk through the best finish option for your situation.

No — and you shouldn't. Sealing or painting over weathering steel prevents the oxide layer from forming and doing its job. Leave it bare and let it do what it's designed to do.

This is normal in the early weeks before the piece is fully sealed. Avoid light-coloured or porous surfaces until the piece has fully weathered (around 3–6 months), and the residue will stop once the patina has stabilised.

Yes — regular watering (as above) is the most effective way to compensate for low rainfall or dry conditions. Even a daily spritz with a hose will make a noticeable difference.