How to install a Colorbond fence in sandy soil?

[Sankari]

Hi Everyone!

I'm planning to install a colorbond fence in the coming months.  I've watched videos by Bunnings and others on YouTube so I think I have the basics clear in my mind.  However, I noticed the soil in all these videos was quite compact and clay-based, whereas the soil where I live is extremely sandy.  Are there any pointers/tips/posts or tutorials that anyone can recommend to help me do a good job please?  

[EricL]

Hello @Sankari 

Installing Colorbond fence posts in sandy soil requires extra care to ensure long-term stability, as sand doesn’t provide the same grip or support as clay or loam. First, it’s important to dig your post holes deeper than you normally would—aim for at least 600mm, and up to 900mm for fences over 1.8 metres high or those in windy areas. This added depth provides more holding power in loose soil. To further increase stability, shape the holes so they are slightly wider at the base, creating a bell or footing shape. This acts like an anchor in the sand and helps resist uplift and lateral movement over time.
 

When setting the posts, avoid rapid set concrete. Instead, use a standard concrete mix or post mix, as it allows for better compaction and bonding in sandy conditions. Be sure to mix it thoroughly and allow it to cure for at least 24 to 48 hours before attaching any fence panels. Before pouring the concrete, compact a 100mm layer of gravel at the bottom of each hole to provide a solid base and improve drainage. While the concrete is setting, brace your posts with timber supports to keep them perfectly plumb—sandy soil won’t hold them upright on its own. It's essential to wait until the concrete has fully cured before installing the Colorbond panels, as adding weight too soon can cause the posts to shift.
 

If you find that the sides of the holes are collapsing while digging, consider using cardboard or plastic formwork to help hold the shape and contain the concrete during pouring. Finally, if your fence is in an area that experiences high wind or water flow, it’s wise to backfill the top of the holes with compacted material or install a concrete collar around the base of each post to prevent erosion and movement over time. With these steps, you’ll give your fence a much stronger foundation and better durability in sandy conditions.

If you need further assistance, please let us know.

Eric

[Sankari]

Hi @EricL! Thank you so much for your amazingly detailed response! I must confess that I was a bit daunted when I first read the pointers you listed, but after re-reading a few times, it all makes sense and sounds do-able. The only thing that I'm unsure about is the concrete collar - is this something I should create with the concrete or something I buy and install?

I really appreciate the pointers and words of caution! I thanks again! 

Sankari

[EricL]

Hello @Sankari 

If you are referring to the formwork, yes, it is something you'll need to specially order at the trade desk. It is a stiff cardboard tube that is used to create footings. You can also use very thin plywood if the cardboard tube is not available.

If you need further assistance, please let me know.

Eric