Why Rock Shows Up Without Warning
Much of Melbourne's west sits on the Werribee basalt plain. Shallow clay, then floaters — lumps and shelves of bluestone anywhere from 200 mm down. Your geotech might flag “possible rock” but the exact depth rarely matches the map until the bucket is in the ground.
We see it weekly on jobs out of Melton into Rockbank, Truganina and old Hoppers Crossing blocks near Derrimut Road. New estates are often pre-levelled, yet detailed cuts for footings still find rock at the toe of the pad.
How Rock Gets Priced (Fairly)
There are two honest ways to handle rock on a site cut:
- Allowance in the quote — e.g. first 2 m³ of rock breaking included, then hourly hammer rate after that
- Day rate with rock clause — fixed price for soft cut, written hourly rate if hammer attachment goes on
Hammer time on a 14-tonne excavator commonly runs $180–$250/hour in 2026, plus extra tipper loads for broken rock. A half-day on a stubborn shelf can add $2,000–$4,000. That's why vague “we'll see on the day” quotes cause fights.
The best rock quote is boring: it tells you the hourly rate and who stops work if it gets worse.
What to Ask Before the Machine Arrives
Get these in writing:
- Hourly rate for rock hammer / breaker
- Who pays if rock is deeper than the allowance
- Extra tipper rate per load for rock spoil
- Whether they'll pause and call you before exceeding an agreed dollar cap
Broken rock weighs more — tipper loads fill faster. Bundle soil removal with the cut so you're not paying a second crew to load out piles later.
FAQ
How much extra does rock add?
Often $1,500–$6,000 on a house pad on the west side, sometimes more on sloping blocks in Sunbury or deep cuts in Craigieburn. The spread is wide because every shelf is different.
Should I get a geotech report?
Your building surveyor usually requires one for the permit anyway. It won't pin every floater, but it flags if rock is likely — useful when comparing quotes.