The Problem

Concrete is often seen as the “go-to” solution for a solid base—but the reality is, most concrete bases fail because they haven’t been installed correctly.
Common mistakes include:

• Not digging out deep enough
• Pouring concrete directly onto soil
• Insufficient sub-base or poor compaction
• Lack of reinforcement (mesh or fibres)
• Concrete laid too thin

In many cases, the slab is installed too high because the correct excavation hasn’t been carried out. This leaves the bottom edge exposed and vulnerable.
Concrete itself isn’t the issue—it’s how it’s installed that determines whether it performs or fails.

When concrete isn’t installed properly, problems develop over time—and they almost always start at the edges.
If the slab hasn’t been dug in deep enough, water gets underneath and causes washout, leading to:

• Cracking around the edges
• Concrete breaking away underneath
• Loss of support across the slab

If the sub-base hasn’t been compacted in layers, the slab can:

• Crack through the middle
• Drop or sink at the back

Without the correct depth or reinforcement, the concrete simply doesn’t have the strength to handle long-term loads.
Once the concrete cracks and begins to move, the building above is no longer properly supported. This leads to:

• Doors and windows no longer opening or closing properly
• Uneven floors
• Structural stress throughout the building

At this stage, the issue is no longer just the base—it’s affecting the entire structure.

If you’re going to use concrete, it must be installed correctly from the ground up. A proper concrete base should follow this process:

Excavation:
Dig out 175mm total depth

Sub-base:
Install 100mm of hardcore or crushed concrete, compacted in layers with a whacker plate

Blinding layer:
Add 25mm of crushed limestone (25mm down) and compact again

Concrete slab:
Pour 100mm of concrete, ensuring at least 50mm sits below ground level to prevent washout

Reinforcement:
Use steel mesh or fibres (If not used, increase to 150mm concrete thickness)

Finishing & aftercare:
Level properly and allow to set
Remove formwork after 2–3 days
Ensure the bottom edge of the slab is not visible