Lest start with one of the primary matters in deciding how your damp issues have come about and how they can be cured: Does your building actually have a DPC? Chances are that if it was built in a traditional way in the last c.150 years it does. (see separate post of those properties without DPCs)
Each row/layer of brick/stone etc is referred to as a ‘Course’, the DPC is a ‘corse’ which holds back damp, the damp in the soil/ground that is present everywhere in differing degrees.
Relatively speaking: Everything below the DPC is designed to be ‘wet’ and everything above the DPC is designed to be ‘dry’.
If it isn’t, then the building isn’t behaving as designed and no amount of masking, putting in a cement slurry barrier, tanking, or whatever is going to cure the fact that your wall, above the DPC, is wet when it should be dry
There are many types of DPC. Indeed the Romans took Lead from Cornwall and used in in buildings all across their empire. New builds (c.1970s onwards to present day), use a plastic membrane. Before then, Slate was very popular, Tar and Tar-felt were used in some parts of the country, mainly major industrial areas. In the wider Midlands a ‘blue brick’ was found to be excellent against damp as well as being decorative.
So can it fail? NO. How does a substance, inert in nature, in the case of slate, millions of years old, fail? It can’t. It can be removed in small sections during bad maintenance and not replaced. But it can’t fail. The minor, and we are talking minor, crack that appear due to structural movement will not cause the building any worry. In the case of Blue brick, there is a damp-pathway between each brick at the mortar line, some 5% (c.5mm) of the width of the blue brick. This isn’t an issue, so if your slate, tar, or other DPC has a crack in it due to movement of greater than 5mm per 100mm run, you have a lot more to worry about with subsidence than damp !