Abstract: It is highly desirable to reinforce the grassed surface layer of a sports ground in order to reduce damage to the surface, e.g. from horse racing or from playing football. In order to provide a good surface layer, a biaxially-orientated, integrally-extruded plastics material mesh structure layer is laid on a base of sand strengthened with small, flexible, randomly-placed, plastics material mesh pieces. A top dressing is put on top of the mesh structure layer, grass is seeded or planted, and a machine is then used after the grass has grown to slit the mesh structure layer into pieces 1 which may be e.g. 100.times.100 mm or 150.times.150 mm, each having a number of complete mesh openings. If a piece is caught by a horse's hoof or by an footballer's stud, it may be ripped out, but the whole mesh layer is not ripped out.