The same thing happened to me Phil on a 50 mtre floor!with the old Dural matting,the customer didn't Evan know its only that I went back 16months later to tile there bathroom went to have a look at the floor I did,all the grout was in tact but a crunchy floor!! So I'd heard a few things in the forum about this happening,and I made a swift call to Dural,they owned up to it and sorted it you should be ok mate... But it does make me wary about using these systems now??