you can add new board over the old board. you have to watch how far out you`re fixtures are stubbed out (so you can screw you`re handels and spouts back on). you also need to use a proper backing depending on the type of finish you`re going to apply: paint, surround material, stone, tile, ect.... also figure how you`re going to finish-cap-return the resulting edges. you shouldn`t have to do much to the plaster board existing. hope this helps and post again if you need to know more.good luck.