I always cut out and remove the existing walls and install new backer board. This gives you a chance to inspect the wood behind the walls, and gives a new surface for the "glue" that holds the new panels. For cultured marble, you will want to use greenboard.
Terry

: Hi, I need to replace the cultured marble panels in our shower, one has a hairline crack. I've installed tile before
: so I'm going to try this. I think the biggest challange will be to get the existing marble out without destroying
: the walls completely. Any tips, both on removing and installing.
: Thanks, Alan