How to Specify Corten Steel for Your Builder or Landscaper (So You Get Exactly What You Want)

Corten steel is a type of weathering steel. When it sits outside, it forms a rusty-looking surface called a patina. That patina is not just for looks. It acts as a shield, helping protect the steel beneath from rusting too far. That is why Corten is popular for outdoor edging, screens, planters, and feature panels.
Because Corten changes over time, you need to consider factors like airflow, water runoff, and where the rust water will go early on. You also want to think about stiffness, because big flat steel pieces can move if they are not supported. These are not scary problems. You need the right spec from the start.

Garden edging

For garden edging, 3 mm Corten is the sweet spot for most homes. It is strong enough to hold a clean line, but still flexible enough to shape gentle curves. Metfab's standard Corten edging is 3 mm thick, indicating this is a proven everyday choice.

Go thicker if:

• You are doing very tall edging that holds back the soil
• You have long straight runs where you want extra rigidity
• You expect heavy knocks, like lawn mowers or foot traffic, right on the edge

When you send your sketch, note the height you want and whether it is decorative edging or a mini retaining wall. That helps us lock the thickness.

Screens and privacy panels

Screens are like big sails in the wind, so thickness and support matter more. If a panel is too thin and too wide, it can "oil can," appearing wavy when light hits it.

A safe way to think about it:

• smaller screens with short spans can use a thinner plate
• Bigger screens need a thicker plate or extra support

The key is not just thickness. It also includes folds and stiffeners, which we will talk about soon.

When you spec a screen, add:

• panel size
• How will it be fixed
• post spacing or frame details

Cladding and wall feature panels

Cladding panels need to stay flat and tidy. A very thin sheet can ripple, especially once it heats up in the sun.

For cladding, your spec should include:

• panel size
• thickness range you are aiming for
• how the panels will be supported behind
• ventilation gap behind the steel

If you want a super clean, flat look, let us know. We can suggest thickness and support options to suit.

Planter boxes and structural features

Planters hold soil and water, so they need to be strong. The base also needs to stay stiff so it does not bow over time.

So in your spec, list:

• planter dimensions
• whether it is freestanding or built into something
• If you want internal bracing
• drainage hole locations

Again, you do not need to guess perfectly. Give us the use case and rough size, and we will recommend the right plate.

Folds, returns, and stiffeners (how to stop warping)

This is the part most people skip, and then wonder why their panel looks like a wobbly potato chip six months later. No judgment. Steel behaves that way unless we help it.

Folded edges and returns

A folded edge occurs when the steel is bent along its edge. A return is basically that fold continuing backwards to form a small "lip." It makes a panel much stronger without making it look bulky.

Returns are useful for:

• privacy screens
• cladding panels
• signs
• feature panels
• planter box tops and corners

They help:

• reduce warping
• keep edges straight
• make the piece feel more "finished"

If you want a clean, crisp panel, ask for returns.

Stiffeners and backing frames

A stiffener is a bar or folded section added to the back to keep a panel flat. Think of it like ribs under a shelf.

You need stiffeners when:

• The panels are wide
• The panels are tall
• Panels are in windy or exposed spots
• You want a dead flat look

If your builder is installing the panel onto a frame, tell us the frame details. We can match the fabrication to suit.

Drainage, airflow, and staining control

Corten loves air and hates trapped water. If water sits on it for too long, the patina can form unevenly. Plus, early rust water can splash or drip onto nearby surfaces.

Drainage gaps

Always plan where the water will go.

Examples:

• Screens: leave a gap under the screen so water does not pool at the base.
• Cladding: allow airflow behind the panel with a ventilation gap.
• Planters: include drainage holes and lift the base slightly so water escapes.

A simple line in your spec, like "allow drainage gap at base”, helps your installer do the right thing.

Staining control

Early on, Corten can run off rusty coloured water. That is normal. Over time, it reduces as the patina stabilises.

To avoid stains:

• Keep Corten a little away from pale pavers or render
• Use gravel strips under edging or screens
• Design drip lines so water falls on soil, not tiles
• Consider sealing only if you have very light surfaces right next to it

If your project is next to light stone or concrete, mention that in your quote request. We can suggest a safe approach.