Reactive clay
Clay soil that swells when wet and shrinks when dry. Common across Adelaide, causes seasonal footing movement and cracking.
Reactive clay soils are widespread in Adelaide, particularly in the suburbs east of the city, the foothills, and parts of the Adelaide Plains. The soil's volume changes dramatically between wet winter and dry summer.
When the soil dries, the ground around your footings shrinks. The footings move with the soil, creating tension in the structure above. When the soil rewets, it expands - lifting the footings back, but rarely uniformly.
The result is seasonal cracking. Inspectors will distinguish between active cracking (which moves with the seasons) and historic, settled cracking. Modern slab classifications (M / H1 / H2 / E for extreme) reflect site reactivity and dictate footing design.
Slab heave
Upward movement of a concrete slab caused by expanding reactive clay underneath. Often visible as raised floors, cracked tiles, jammed doors.
Stepped cracking
Cracks that step diagonally through brick mortar joints, following the path of least resistance. Common indicator of foundation movement.
Footing movement
Movement of the building's foundations, usually caused by reactive soil, water entry near footings, or undersized original footings.