or finishing the start, I am not sure...
Back in June last year we published a photo of the slates on what was once the outside of the staircase tower. We had to work quite hard to convince the labour force that we wanted the slates left in place as a historical document and evidence of the building's history, but we managed it. All we did at that time was apply 2 layers of glass wool insulation to the slates, tied and taped.
This left the other side of the wall as a bit of a problem: the tiles are hung on laths nailed between upright posts. Although this is terribly authentic, it isn't very aesthetic, or indeed easy to keep clean. There is a lot of couple of hundred years of dust up there, which will be almost impossible to keep from entering the rest of the house.
In order to get the mixture to stay on the wall you need to provide support, which we have done with a new framework within the uprights. This will eventually be hidden by the mortar, which will be applied in a couple of 2" (5cm) layers.