Patent ID: 7484338

Claim:
A locking system for mechanical joining a plurality of floorboards, each of the plurality of floorboards having a body, a first joint edge portion and an opposite second joint edge portion, and a balancing layer fixed to a rear side of the body, the first joint edge portion and the second joint edge portion of adjacent ones of the floorboards are adapted to be joined together at a vertical joint plane, said locking system comprising: a first connector for vertical joining of the first joint edge portion of a first floorboard and the second joint edge portion of an adjoining second floorboard, the first connector including a tongue groove formed in the first joint edge portion and a tongue formed in the second joint edge portion; a second connector for horizontal joining of the first joint edge portion of the first floorboard and the second joint edge portion of the adjoining second floorboard, the second connector including a locking groove formed in an underside of said adjoining second floorboard and extending parallel to and at a distance from the vertical joint plane at said second joint edge portion and having a downward opening; and a strip integrally formed with the body of said first floorboard, the strip at said first joint edge portion projecting from said vertical joint plane and having a locking element at a distance from the joint plane, the locking element projecting towards a plane containing an upper side of said first floorboard and having at least one operative locking surface for coaction with said locking groove and the strip forming a horizontal extension of the first joint edge portion below the tongue groove, wherein the balancing layer of the first joint edge portion, within at least a portion of a first area defined between a bottom of the tongue groove and the locking surface of the locking element, is completely or partially removed, wherein partially removed includes an alteration of a thickness of the balancing layer.