Hi i am converting a downstairs room into a shower room,where the plaster on the walls is in very poor condition.I intend to fix plasterboard on to the existng walls which will then be tiled from floor to ceiling.As the walls will be completely tiled will oridinary plaster board be ok.Secondly i need to raise the floor by 2 cm so i have used some chipboard i had in the garage which i have screwed to the concrete floor.Will this be ok to tile onto?