Chris Plastow
I can't say if your chimney needed rebuilding or not but the condition you are experiencing is called ammonium sulphate contamination. This salt is inherent in the flue and absorbs moisture (hygroscopic ) from the atmosphere. Ensure the chimney flue is well ventilated, remove the internal render to all those places showing damp +400mm in each direction. Replace with waterproof render. This is not to stop the damp but the salt migration through the render. This is a common but little understood condition.
