Our house was built in 1922 with sandstone walls 4 foot wide. In the late 90's the house was totally refurbished with the internal walls covered with a concrete render and plastered with gypsum after they were tanked. It seems to have been alright until earlier this year when my wife decided to repaint the place. The paint has all bubbled and white powder has appeared. We have been advised to either take off the plaster and render to the original stone or just the plaster ,then fix battens to the render before plasterboarding and skim.
Any thoughts on the best solution?