We have a shower in our master bath with two walls of cultured marble. Rather than ripping out that cultured marble can we tile over it with a mosaic marble tile? There is a very intricate octagonal window in one of these walls that we do not want to remove because it is beautiful & it cost a lot of $ to install. That trim is also out of the cultured marble & it protrudes far enough from the shower wall to put a mosaic tile up to it. If this can be done, how would the cultured marble walls be prepared to accept the new tile & what type grout should be used? Thanks for any help!