 If a damp-proof course is present, it is likely to be functioning, as the materials from which damp proof courses are manufactured tend to have a long lifespan.However, it should be acknowledged that there are cases where existing damp proof courses fail for one reason or another.One indicator that is often used to determine if the source of dampness is rising damp (rather than other forms of dampness) is to look for the presence of salts – in particular a tell tale "salt band" or "tide mark" at the peak of the damp's rise.