I live in a 1935 semi-detached house with no cavity on the exterior walls. It has been rendered years ago. My son’s bedroom on 1st floor is extremely cold and has black on the walls. I have had this replastered, I have had the windows replaced & brickwork repointed. The render is cement render. Do I need to use a special render (ie lime render) to allow the property to breathe? or could this just be condensation. Where will I find a specialist lime renderer if I do need one?