26 The arbitrator limited the contract documents to those set out above. The documents he specified were less than those asserted by the Villanis as comprising the partly oral, partly written, contract with partly express and partly implied terms. The arbitrator provided no reasons for the exclusion. He did not determine whether other documents were part of the contract or whether the contract included oral terms. He failed to deal at all with the assertion that the contracted practical completion date was 20 September 2000. It is not of course necessary for an arbitrator to deal with every issue which arises, or every argument or submission put forward. An arbitrator must, however, deal with the substance of a claim or counterclaim, particularly those matters which will materially affect the result. In the circumstances, the issues as to what constituted the contract and what was the contracted date of completion being so central to the Villanis' counterclaim, I find that the arbitrator omitted to determine all the necessary issues and controversies within the arbitration. I further find that the issue as to the contracted completion date was a material fact which may have influenced the award.