I've tried telling the customer all this, but at the end of the day that's all we can do, if he wants to go down the electricians route then that's up to him, all I'm interested in is whether or not it's suitable to tile too.
Andy, until you know exactly what he is proposing to put down you can't ask your adhesive supplier if they do a product suitable to fix to it. They well do but it may cost an arm and a leg