A covering unit for use in combination with similar units for covering a surface with a natural random look, the unit having an hexagonal body comprising first, second and third pairs of opposed and parallel sides. Each side has a central point of angular symmetry. The second and third pairs are similar to each other while the first pair is different from the others. The sides of the second and third pairs are provided with at least one split deviation along their length arranged so that each side of the second pair is a rotational image of the sides of the third pair, whereby in use in combination with other covering units: each side is matingly engageable with the sides of an equivalent pair of a neighbouring unit; and the unit has a central point of angular symmetry and is matingly engageable with a plurality of neighbouring unit.