Hi Martin,
Use the Model.CoveredRanges property of the grid to manage the covered ranges in a grid. Please try the attached sample and let me know if you are looking something different.
this.gridDataBoundGrid1.Model.CoveredRanges.Add(GridRangeInfo.Cells(1,0,this.gridDataBoundGrid1.Model.RowCount,0));
Sample:
GDBGMergeCell.zipBest regards,
Haneef