Sinking Slabs — What Causes Them?

A sinking slab is more than an eyesore — it’s a structural and safety issue.

Poor Compaction

If the ground beneath the slab isn’t compacted properly:

• The soil settles over time

• The slab follows

• Cracks and level changes appear

  
  

Uncontrolled Fill

Using fill material without proper testing or compaction is risky.

Problems include:

• Differential settlement

• Slab tilting or dropping

• Cracking around edges and joints

  
  

Water Ingress

Water washes away fine soil particles beneath slabs, leading to voids and collapse.

Sources include:

• Poor drainage

• Leaking pipes

• Surface water ponding

  
  

CWG NSW Prevention Strategy

✔ Removal of unsuitable material

✔ Layered compaction

✔ Drainage control

✔ Correct slab thickness and reinforcement

Fixing sinking slabs is costly — preventing them is far cheaper.