Just a quickie, any reason why normal quarry tiles cant be used externally. I know terracotta can be susceptible to frost but is that likely to effect them? Any problems with them being slippery? etc etce etc he asks waiting for the deluge of answers!
No reason at all - thousands of Victorian houses had quarry front paths and steps and are still good today. Sand/cement bed I would suggest, rather than adhesive although no doubt some-one will correct me on this point!