Latest News:

How To Avoid Construction Disputes – Maria Fisentzou Diales nominated in Structural Awards 2019 Diales are delighted to announce that Phil Duggan been appointed as Head of Diales for the Middle East Diales are proud sponsors of Asia ADR Week 2019 Diales are pleased to be sponsoring the 5th ICC Asia Conference in Singapore Diales are pleased to be sponsoring the 4th ICC Africa Conference in Lagos this week Diales is proud to be sponsoring the 3rd PAW and to host a conference Diales is delighted to be taking part in the 3rd Kuwait Project Management Conference 2019. Diales is proud to be sponsoring the 7th ICC MENA Conference on International Arbitration Dealing with conflicting pressures – A practical guide Diales Technical are shortlisted for an award. Diales are proud sponsors of the CIArb’s International Arbitration Conference 2018 Flying high! Another Goodwood sculpture success Diales is proud to be sponsoring the 4th ICC Asia Conference on International Arbitration Diales Host Drinks Reception GAR Live Construction Disputes ICC Institute Advanced Training on “Drafting enforceable awards” Should arbitration in investment protections treaties be forsaken? DRBF Conference – Paris, France Diales work with Gerry Judah on a new sculpture – Jacob’s Ladder Damp in Listed Buildings Diales experts gain professional recognition Diales have two new experts Diales host successful drinks reception Diales are commended at the 2017 Structural Awards Mark Castell is attending the 2017 Dutch Arbitration Day, Amsterdam Independence Day: Why Do Many Experts Fail at Being ‘Independent’? John Mullen is published in the Construction Law Review Diales technical are shortlisted for two awards Diales celebrates five years of dedicated Expert Witness support services ICC 1st European International Arbitration Conference

Expert Profile

John Mullen

John Mullen

Principal and Quantum Expert



Memberships & Associations


Contract Experience


Presentations & Training

Extensive lecturing on construction commercial issues both in-house and publicly


Oil & Gas
Process & Industrial

Regional Experience

Middle East
United Kingdom


  • Chartered Quantity Surveyor and Chartered Civil Engineering Surveyor
  • Over 35 years of engineering and construction experience
  • Specialist in the evaluation of construction claims
  • Over 70 international expert appointments
  • Appointed on disputes up to $790 million in value
  • Cross examined on many occasions, including 10 times by specialist Queen’s Counsel
  • Oral tribunal evidence to some of construction’s most eminent judges and arbitrators


A chartered quantity surveyor and chartered civil engineering surveyor, John has over 35 years’ experience of the construction industry. In that time he has been employed by contractors and professional practices and represented public sector bodies, private sector employers, architects, quantity surveyors, insurers, accountants, contractors, sub-contractors and materials manufacturers.

John trained with a national firm of contractors as a site based quantity surveyor on building and engineering projects, contracted on traditional, cost plus, and management bases, he also worked for local small builders pricing building works.

Over the last 30 years John has specialised in providing consultancy services to the construction industry. This has included pre-contract and post-contract quantity surveying activities, project management, and claims services acting for employers, contractors, subcontractors, insurers, and other construction professionals.

John has worked as expert on building projects up to $790 million, and infrastructure projects up to $760 million, in dispute. He has an international reputation that has led to over 70 appointments as an expert witness, including acting as joint expert. Cross-examined on numerous occasions, including several times by Queen’s Counsel, John’s expert commissions have involved the UK Courts, UNCITRAL, LCIA, ICC, DIAC, ADCAC, AFSA, and ad hoc Arbitrations. He has given evidence in various areas including aspects of pre and post-contract surveying; the measurement and valuation of work done; variations; termination costs and claims for suspension prolongation; acceleration; and disruption.

John’s main areas of technical specialisation are in dealing with difficult final account and claims issues; valuation issues; variation issues; and claims topics including the financial effects of termination, suspension, delays, prolongation, disruption, acceleration, cost escalation, plant depreciation, preliminaries thickening, overheads, and loss of profit claims.

John is co-author of two industry publications:

  • Evaluating Contract Claims, 2nd edition, Wiley Blackwell, 2008
  • The Expert Witness in Construction. Wiley Blackwell, 2013