I am going to lay tiles in a small guest toilet (not a wet room) in the ground floor where the floor is concrete on the base slab, i.e., uninsulated. The question is whether I need to apply a moisture barrier or not. Isn't it better not to do it because any moisture that comes through the base slab (70s house - no insulation under the footing) will be ventilated away? Otherwise, it will be trapped in the slab/concrete?
If it had been mine, I would have easily skipped the tätskiktet 
