Hmm. That is a very big question I think David as failure diagnosis can be complicated and can sometimes be subjective. When I do come across failures there is often not one cause it a combination of effects which gang p to cause the failure. It is often very difficult to do not least of all because when there is a failure people tend to og into self preservation mode and don't always tell the facts. Also I come across a lot of people who tell the stories as they see them and you then get a completely different story from a second party.
I try to use logic, elimination, common sense, experience and science to determine reasons for failure. What I have learned to do though is avoid assigning responsibility to one or other party as I often find the facts are not as simple as they they can appear.
By way of example I am dealing with an issue at the moment advising a client about the "facts" behind his screed failure wich has led to the
tile failure. I ambeing asked as the "expert" who is responsible for the failure and what theunderlying cause is. Having examined all theinformation I have been presented with I have found that the first failure was the architects design, this was then changed slightly by the builder making the issue worse, then the underfloor heating was installed badly and without due diligence and then the screed was incorrectly installed and then the tiles were incorrectly installed. To top the lot theunderfloor heating was turned on at high temperature thermally shocking the floor. All I can really do is point out at each stage where the deficiencies are. I was told that the client believes itis the fault of the underfloor heating and the thermal shock. Actually all of the other elements could have contributed or caused the failure as well. Nightmare.
I love my job sometimes....