A building product comprising a composite board having a cellular, non-elastic core, top and bottom board surfaces, and a facer comprising a non-cellulosic fiber mat substrate; and a water-based overlaying material applied to the composite board. The building product may also comprise an undersiding; a composite board having a cellular, non-elastic core and top and bottom board surfaces and facer comprising a non-cellulosic fiber mat substrate fixed to the undersiding; a reinforcing layer fixed to the board; and a water-based overlaying material applied to the reinforcing layer.