Adding DataRow to DataTable

I am trying to add a DataRow to a DataTable after adding some cells to the row. That datatable is then bound to the datagrid.
But on the browser I see this in the first cell and rest of the cells are empty:
System.Web.UI.WebControls.TableRow

This is what the line of code looks like:
_mainTable.Rows.Add(RowToAdd);
what am I doing wrong?
Thanks for your help.