Prove It or Lose It – What Mainteck v Stein Heurtey Teaches QS Experts
This case involved a subcontract between Mainteck and Stein Heurtey for works on an industrial plant in New South Wales.
Mainteck alleged that design changes, interference, and late instructions caused it to work inefficiently and incur major additional costs. It presented what was, in effect, a global or total cost claim – saying that its labour and costs had increased overall because of the disruptions caused by the head contractor.
A referee found that the events had “significantly interrupted” the works and that “in all probability” they had caused the loss. The trial judge accepted that view and awarded Mainteck damages.
On appeal, the New South Wales Court of Appeal disagreed. It held that while the referee had used language of probability, there was not enough evidence to connect specific events to the measured losses. The findings did not meet the required standard of proof.
What the Court Said
The Court of Appeal made a key distinction between possibility and proof. It accepted that many causes can operate together on a construction project, but the claimant must still show that each significant cause of loss is attributable to the other party.
The court said:
“In a global claim, if a significant cause of loss is not attributable to the defendant, the claim fails.”
That single sentence remains one of the clearest expressions of the law on quantum proof. It means that if even one material portion of the cost overrun was caused by the claimant’s own inefficiency or other neutral factors, the whole claim may collapse.
The Court was not prepared to rely on broad probability. It wanted evidence showing how each cost component flowed from an identified event or breach.
The Lesson for Quantity Surveyors
For QS experts, this case reinforces the same message as John Holland v Kvaerner but in even sharper terms. Courts expect causation to be shown, not assumed. It is not enough to say “the project was delayed, therefore costs rose.” The expert must demonstrate the logical and evidential link.
A reliable QS expert opinion will therefore:
Track causes to effects – identify which directions, delays, or design changes produced measurable additional cost.
Deal with competing causes – acknowledge when more than one factor contributed and assess their relative weight.
Stay within the evidence – opinions must be based on contemporaneous documents and factual findings, not general impressions.
This case also highlights a subtle but critical point. An expert who overstates certainty or ignores the role of other causes risks being seen as partisan rather than independent. The Court of Appeal made clear that it will not fill gaps where the expert has failed to deal with contrary evidence.
Why This Still Matters
Global or composite claims are still being advanced in large projects, often supported by expert reports that rely on probability and broad assumption. Mainteck confirms that such reasoning will not hold. Courts expect experts to apply forensic discipline, to separate the measurable from the speculative, and to accept that sometimes parts of a claim cannot be proven.
Forensic quantity surveying is not advocacy. It is disciplined analysis rooted in cause, cost and fact. Mainteck shows what happens when that standard is not met – the claim may be technically plausible but legally unproven.
Final Thought
In my view, this case draws a clear line between opinion and proof. A quantity surveyor can analyse and assess, but the court decides. Our job as experts is to present reliable evidence that enables the court to make that decision with confidence.
When an expert treats probability as proof, the evidence loses weight. When a QS provides a clear, balanced explanation of what is proven, what is uncertain, and why, the court is far more likely to accept it.
Mainteck reminds every expert that it is better to be precise than persuasive. Facts speak louder than assumptions.
At Accura Consulting, our team of experts work with clients to create a tailored solution to problems. If you have an issue and want expert support, get in touch.
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