i have another job to tile over metro tiles with 600x300 wall tiles,the metros have been put on over sand and cement and are going to be very difficult to get off,as there are voids in the wall could i use neat pva and skim over to get a flatter surface to work to and then tile over just wondering would it work,or batten and board,the last job i did over tiles used a lot of adhesive and there was some lippage,or should i walk away,thanks