When I was 15 I spent most of my summer holidays hacking the bottom 18" of plaster off the ground-floor walls of our house, applying bitumen and replastering. The wretched builder had put a DPC under the flooring and a DPC in the walls, but hadn't joined the two so that the plaster wicked up the moisture, softened and bulged out under the wallpaper, which also looked a bit sad.
No compensation from the builder, either: he had started a firm to build & sell the houses then pocketed the money and closed down. You could do that easily in the 1950s. He was 12 years gone by the time my dad decided to tackle the walls himself, and I pitched in as well. As it happened I did 90% of it - horrible job.