Colorbond C-Channel Posts: The Complete Guide
C-Channel posts are the backbone of every Colorbond fence. Here''s what they are, what sizes you need, how to set them correctly, and how to choose the right post for your fence height.
Every Colorbond fence starts with the posts. Get the posts right — correct size, correct spacing, set correctly in concrete — and the rest of the fence goes up quickly and lasts for decades. Get them wrong, and you'll have a fence that leans, sags, or fails at the first strong wind.
At Wallan Fencing and Timber Supply, we stock Colorbond C-Channel posts in the sizes needed for standard residential fencing in Wallan and across Mitchell Shire.
What Is a C-Channel Post?
A C-Channel post (also called a Colorbond fence post or lipped channel post) is a roll-formed steel post with a C-shaped cross-section. The lips of the C face outward, creating channels that the fence rails clip or slot into. This design makes rail installation fast and secure — no drilling, no bolts, just clip in and go.
C-Channel posts are made from Colorbond steel, so they're available in the same colours as the fence sheets. They're hot-dip galvanised on the inside and Colorbond-coated on the outside for maximum corrosion resistance.
Post Heights: What Size Do You Need?
Post height depends on your fence height and how deep you need to set the post in concrete.
For a 1.8m fence, you typically need a 2.4m post — 1.8m above ground and 600mm in concrete.
For a 2.1m fence, you typically need a 2.7m post — 2.1m above ground and 600mm in concrete.
The general rule is: post length = fence height + minimum 600mm embedment. On soft or sandy soils (less common in the Wallan area, but worth checking), increase embedment to 750mm or more.
Post Spacing
Standard Colorbond fence post spacing is 2.4m centres (measured from the centre of one post to the centre of the next). This is the spacing the fence rails are designed for. Going wider than 2.4m will cause the rails to deflect and the sheets to rattle in wind.
On corners, gate openings, and ends, posts are set closer together — typically 100–200mm from the corner or gate post.
Setting Posts in Concrete
- Dig holes to the required depth (minimum 600mm) and 200–250mm diameter.
- Check alignment with a string line before pouring concrete.
- Brace posts while concrete sets — at least 24 hours, ideally 48 hours before fixing rails.
- Use rapid-set concrete if you need to continue work quickly. We stock Rapid Set concrete at our Wallan yard.
- Check plumb in two directions before the concrete goes off.
How Many Posts Do You Need?
Number of posts = (Total fence length ÷ 2.4) + 1
For a 30m fence: (30 ÷ 2.4) + 1 = 13.5 → 14 posts (round up and add 1 for the end post).
Add extra posts for corners, gate openings (2 gate posts per opening), and any changes in fence direction.
Matching Post Colour to Fence Colour
C-Channel posts are available in Colorbond colours to match your fence sheets. The most popular colours in the Wallan area are Monument, Woodland Grey, and Ironstone. If you're matching an existing fence, bring a sample or note the colour name before ordering.
What Else Do You Need?
A complete Colorbond fence requires:
- Fence sheets (Trimfort or Zigzag profile)
- Fence rails (top, mid, and bottom)
- Post caps (to seal the top of each post)
- Concrete for setting posts
- Tek screws for fixing sheets to rails
We stock all of these at our Wallan yard.
Available at Wallan Fencing and Timber Supply
We stock Colorbond C-Channel posts at our Wallan yard, with same-day pickup available. We supply homeowners, tradies, and builders across Mitchell Shire — including Kilmore, Broadford, Seymour, Beveridge, Craigieburn, and Donnybrook.
Call us on 0431 193 102 or get a quote online.
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