The classic cottage problem: a solid wall, a chimney breast and a tide mark of damp creeping up behind the paint. The plaster was soft and salty to about a metre.
We sheeted the room, hacked the affected plaster back to the brick around the fireplace and under the window, and treated the wall. Then it was left to dry properly before we came back to render and re-plaster. Stripping it back like this is the only way to be sure the salts are gone and the new finish will last.