Abstract: A separation layer (12) for laying grass surfaces (10; 16) on a sand or gravel base (13), which layer is in the form of a rigid plastic sheeting with parallel side edges. The surface of the sheeting is embossed by thermo-forming so that it presents a uniform pattern of deep embossings (14). These form rows which extend perpendicular to said side edges. The parallel rows are each connected to adjacent embossings in the same row via bridges (15) so that each row of embossings in cooperation with adjacent rows creates a stiffening of the sheeting.