Abstract: A waterproof board for use as a backing surface comprising a top face, a bottom face, a plurality of sides, a core layer having a thickness of about 5 millimeters, and a sound layer having a thickness of about 2 millimeters. The sound layer is generally interconnected to the core layer. The core layer may comprises at least two faces, either of which may comprise a textured surface. The textured surface may comprise either a substantially smooth finish or a substantially abrasive finish. The core layer comprises a densified foam material having a density of 490 kg/m3 to about 520 kg/m3, and a specific material composition, both of which enhance waterproofing and attain an optimal balance between rigidity and severability.