Finishing the start of that job.

It's weeks since I wrote that we were starting to finish the insulation of the staircase tower. Since then the job has been finished, but what with spending all my time in the car park at Chenonceau I really have not had time to write about the next steps.

After putting the framework in place, Stéphane first applied a very rough 50/50 mixture of cement and chaux (lime) with enough water to hold it together. This was to give the chaux chanvre something to grip onto and was applied from a distance by being thrown at the wall. It wasn't a thick layer, nor did it give complete coverage.

The first layer of cement isn't really a layer

After that had dried, it was time to apply the real insulation. The next 2 layers were a real treat - a light, foamy mixture with the consistency of Chantilly cream. The recipe is:
50 litres of chopped chanvre (hemp)
25 litres of chaux aérienne (CAEB 90)
25 litres water

After the first layer of chaux chanvre. You can
see how messy the process is.

These layers were also thrown at the wall from a distance, but because of the looseness of the mix it involved constantly pushing the mixture back into the voids. Just like working with whipped egg whites, however, it was important to avoid working the mixture too much and losing the air. We allowed three days between layers, each about 5cm (2 inches) thick.

The second layer of chaux chanvre in place.
By this stage there was gunk everywhere.

Another three days later it was time for the final coat. This was a mixture of:
½ bucket chaux aérienne
½ bucket fine (0-2mm) white sand
1 bucket chanvre
½ bucket water (more or less)

This was of a more traditional gloopiness, more like cement, and trowelled into place. This involves plenty of muscle power as you are trying to get a slightly glazed looking finish.

Before the final layer was applied the wood was cleaned.
You can now start to see the final effect.

This will eventually dry to almost white - a process that will take a couple of months to complete. This means that wall of the staircase tower will have 20cm (8 inches) of glass wool and 15 cm (6 inches) of chaux chanvre insulation and provide as much insulation as the other walls, which are one metre thick.

Simon