As the weather starts to improve and fencing season begins, most people start planning their new garden fence. And while measuring, levelling and post spacing are all important, there’s one crucial factor that will determine whether your fence stands straight for years or leans like the Tower of Pisa by autumn: Postcrete.
Postcrete (often sold as “Ready Mix Post Concrete”) is the easiest, fastest and most reliable way to fix fence posts into the ground — even if you’ve never used it before.
Here’s everything you need to know, including how much to use, how big your holes should be, and a few insider tips that will save you a lot of stress later.
What Is Postcrete?
Postcrete is a pre-mixed blend of cement, graded sand and fast-setting additives.
It’s designed specifically for:
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Wooden fence posts
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Concrete posts
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Metal posts
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Gate posts
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Garden structures
The appeal is simple: just add water.
There’s no mixing, no mess, and no waiting around — it normally sets in 5–10 minutes.
How to Use Postcrete (Step-by-Step Guide)
Using Postcrete really is as easy as advertised. Follow these steps:
1. Dig the hole
Dig to the correct depth and width for your fence post.
(Don’t worry — we explain the recommended sizes further down.)
2. Add water first
Fill the hole with water to about one-third of the depth.
3. Pour in the Postcrete
Pour the bag evenly around the post until no standing water is visible.
The powder should fully cover the water surface.
Tip: You can add a small splash of water on top if needed.
4. Position and level the post
You have around 5–10 minutes before the post begins to set, so work quickly.
5. Finish the surface
Once set, cover the top of the concrete with soil, grass or decorative finish.
That’s it — your post is fixed.
Pro Tips & Tricks for Perfect Fence Posts
⭐ 1. Use temporary braces
Scrap timber makes ideal support braces.
They hold your post level while you pour and set the Postcrete.
Once the concrete has hardened, correcting a wonky post is a nightmare, so this step is worth the extra minute.
⭐ 2. Use a helper
A second pair of hands reading the spirit level means straighter posts and faster work.
⭐ 3. Wear PPE
Postcrete dust is unpleasant and shouldn’t be inhaled.
Wear a mask and eye protection — even outdoors.
⭐ 4. Keep a “poking stick” nearby
A bit of roofing batten, spare timber offcut or bent rebar will do the job.
Sometimes the mix needs a quick poke to move around the post evenly.
How Big Should a Fence Post Hole Be?
Below is a simple guide showing recommended hole sizes and how many bags of Postcrete you’ll typically need:
| Hole Width | Depth | Duty Rating | Approx. Bags of Postcrete |
|---|---|---|---|
| 150mm / 6" | 600mm / 24" | Very Light Duty | ½ bag |
| 200mm / 8" | 600mm / 24" | Light Duty | 1 bag |
| 250mm / 10" | 600mm / 24" | Medium Duty | 2 bags |
| 300mm / 12" | 600mm / 24" | Heavy Duty | 3 bags |
These calculations are based on the approximate volume of concrete needed.
Your actual usage may vary depending on your soil and digging accuracy.
Understanding Light, Medium & Heavy Duty
These aren’t official engineering terms — they’re practical guides based on typical wind load and fence weight:
Very Light Duty
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Picket fencing, decorative edging
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Not suitable for full-size fences in South Wales
Light Duty
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Sheltered gardens
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Light panels or lightweight cladding
Medium Duty
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Standard UK gardens
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Exposed to occasional storms (e.g., “Storm Geoffrey”)
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Ideal for heavier, premium fence panels
Heavy Duty
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Coastal areas
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Hilltops or very exposed locations
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If your washing line regularly attempts to migrate into the next postcode — you’re in this category
Are These the Recommended Hole Sizes?
These are general guidelines that work for most gardens.
In reality, the goal is to use the right amount of Postcrete, not dig a perfectly symmetrical textbook hole.
For example:
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If your ground is rocky, you may struggle to dig a 10" x 24" hole
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In that case, an 8" x 36" hole may give the same concrete volume and stability
If you want to get technical, each bag contains around 20 litres of concrete.
You can calculate the exact volume of your hole using:
Volume = π × radius² × height
But unless you’re digging with laser precision, we recommend sticking to the rough guide above and having an extra bag on hand.
Need More Advice?
If you have any questions about Postcrete, fence posts or hole sizing, our team is happy to help.
Call us on 01656 745959
We’ll always point you in the right direction.