The present invention relates to a jointing system for forming curves or corners in a board, such as a light-weight board, in an easy way. The jointing system according to the invention comprises a first and a second board, adapted to be joined at an angle to each other, preferably at an angle of about 90 degrees to each other. Each of said boards, comprises a lightweight core formed as a three dimensional body presenting a first and a second face and four side surfaces connecting said first and second faces. At least one of said surfaces of each board is miter cut to present a first mitered surface of a first board, and a second mitered surface of a second board. Each of the mitered surfaces are adapted to abut the other and thus to form a miter joint. Each of the parts of the board comprises an aperture into which an insert is adapted to be inserted. The insert, in turn, presents a cavity into which a leg of corner connector is insertable. The first leg and the second leg of the corner connector form an angle of < 90 ° to each other, and the first and/or second leg of the corner connector taper towards their free end.