The assessment of the facts pleaded by the parties in the arbitral proceedings and of the evidence gathered in the course thereof cannot be challenged by means of an application to set aside the award, since such assessment is contractually entrusted to the institutional competence of the arbitrators.
The ground of nullity under Article 829(1)(10) of the Code of Civil Procedure arises where the arbitrators have failed to decide the merits, thereby committing a procedural defect, and does not arise where the arbitrators have rejected a claim on substantive grounds.
The nullity of the award for failure to rule on claims and defences of the parties, pursuant to Article 829(1)(12) of the Code of Civil Procedure, is available only in the event of a failure to examine questions of substance and not questions of procedure.
In arbitral proceedings, a breach of the right to be heard must be assessed not from a formal standpoint but by ascertaining whether the ability to plead and to respond has been effectively impaired, and the award may be set aside only where the allegation of the defect is accompanied by an indication of the specific prejudice caused to the right of defence.