Building With Cob
Cob walls deteriorate for various reasons. In some cases it's because of water damage or movement in the foundations. Most Devon cob buildings are built on stone others are built straight on subsoil, which can cause serious damp problems. The first priority is to inspect the fault and identify the cause of any cracking or damage.If cracks arise around windows and door frames it's often because of decaying lintels, which although in itself is a serious problem, can be remedied. If a gable end has cracked, and this extends to the roof, then it needs serious attention. Old cracks are of less concern than new ones as the latter can indicate recent movement.
Cement render is not the answer and causes further deterioration of the cob as it traps in moisture. This also applies to buildings that have a new concrete floor laid with plastic damp proof membranes which can also cause damp to rise up the walls.
Repairing cob is a skilled job that can take several forms. Mass cob repairs can be done by mixing subsoil with straw; smaller repairs can be undertaken with cob blocks and cob bricks. The method of repairing a wall in this way is referred to as 'stitching.'
By using cob, the existing structure can be matched, not only visually but more importantly, with porosity and density of building materials with a similar compressive strength to the original cob.
Stone plinth constructed with lime mortar. Two lifts of cob added and left to dry.