Gilgai clay and cracking in Kalkallo homes
Why the basalt plain clay under Kalkallo moves, what normal cracking looks like, and when a crack needs measuring.
In short: Reactive clay moves with moisture, and young homes show it as corner cracks and sticking doors. Measure, monitor and keep drainage working; escalate when cracks widen or come back.
The ground under Kalkallo
The suburb sits on the Gilgai plain, named for hummocks that form when reactive clay heaves and shrinks. Lots on this kind of ground are commonly classed highly reactive, with the real class on each lot's soil report.
What movement looks like
Diagonal hairline cracks from door and window corners, cornices separating, doors that start to bind and gaps opening at skirtings.
When it is a defect
The Guide to Standards and Tolerances 2015 sets crack widths and conditions that are defects for each material. We measure each crack and say where it sits.
Keep water consistent
Ground falling away from the house, downpipes connected and garden beds kept off the slab edge all limit seasonal movement.
Written by our local inspection team from work carried out in Kalkallo. Licensed building practitioners, Building & Plumbing Commission registration CDB-U 53425.
