A substrate covering system includes a plurality of elongated board members, which are, for example composed of an extruded thermoplastic material. Preferably, each of the elongated board members has a convex inner surface and a concave outer surface, both of which are flattened as the edges of the board member are attached to the substrate. Preferably, the inner surface has notches facilitating adhesive attachment to the substrate, while the outer surface has grooves curved to simulate a wood grain and to prevent slipping. The system may also include an elongated edge trim strip that can be configured to cover several different types of substrate edges.