My wife and I have just purchased a converted barn in Cumbria. The front room has 3 external walls with pebbledash on 2 of the external walls. The house is sandstone construction with a hollow cavity wall. From the floor to about 3 foot up the lime render has turned to powder due to damp. It appears that there have been multiple repairs over the years using cement in patches. How should we attack these issues??? Should we remove all of the lime and SBR the walls??? replaster with lime plaster?