Thanks for all the advice. After fuller inspection the wall to be chased is 4" block and as I only have to run 15mm & sleeving I shall use sds with chasing tool (don't fancy the dust from grinder as can't properly seal door).
Gray0689 I assume your comment refers to my original query. As a person who has been forced to have a career change later in life I have done everything I can to get "properly" trained. Perhaps if you more experienced plumbers were prepared to take people like me on then I could complete my training on the job. As it is I do an exceptional job for all of my customers & follow all relevant legislation and guidelines. However, there will always be times when my lack of experience means that I am unsure of the best way to tackle a problem. It is for this reason that I have joined this site. There are often different solutions to a problem and this site allows me to see how other more experienced people tackle the same problem. My apologies if my "problem" was not complicated enough for you. Perhaps you are of the opinion that unless I served an apprenticeship as a 17 yr old that I have no right to try to become a plumber at all.