The owner of a Devon cob property based in Exeter wanted repairs carried out to the boundary cob wall.
The cob wall was showing signs of deterioration. Previous inappropriate cement-based renders had been applied to the cob wall. Over time cracks had developed in the render allowing the ingress of water and the slow deterioration of the underlying cob substrate. Cob walls need to be able to “breathe” through lime-based finishes.
It was decided that the cob wall would be taken down to meet the height of the adjoining boundary wall.
First, the roof tiles were removed and put aside for reuse. The cement render was carefully removed. The cob wall was then carefully taken down to a level surface ready to receive a small timber structure which was fixed securely into the cob wall. This would support the roof tiles. The salvaged roof tiles were refixed. Now the cob wall was protected from the elements the cob repairs could begin.
Where the cob wall had deteriorated, cob blocks were bed in lime putty mortar and other areas dubbed out using stone. Once all the cob repairs had been completed, the lime putty render could then be applied.
The lime putty render coats consist of a harling coat, this helps to consolidate the cob wall and provides a key for subsequent lime putty mortar. Haired lime putty mortar scratch coats are then applied to even out the surface of the cob wall. The topcoat would be a non-haired coat of lime putty mortar which could be applied with a trowel and floated to provide a smooth finish or a harled coat depending on the desired finish. A limewash finish could be applied but the owner preferred the natural appearance of the lime render.