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 We had to work quite hard to convince the labour force that we wanted the slates left in place as a historical document and evidence of the building's history, but we managed it.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.
Looking up toward the top of the staircase tower.We have therefore decided to infill the sections between the uprights with chaux-chanvre, a mixture of lime mortar and hemp straw. This will give us a very traditional looking finish that also has insulating properties. The effect will be colombage (what is know in England as "half timbered") where the uprights are still visible, but the spaces between infilled with a mortar mix.
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.
The new inner frameworkAdded to the wooden framework there are rows of nails, which will help hold the mortar in place while it dries. Eventually the mortar will eat its way through the nails, but by then the mortar layers will have bound together and be completely stable.
Nails to hold the mortar bound together.We are not sure how long this procedure will take: not that it is in itself a long task, but there are plenty of other jobs having to be done at the same time before winter arrives.