Many old buildings are constructed from relatively soft and porous materials such as brick, cob and some stone. Paint lime or Lime putty based mortar was normally used for bedding and plastering. The walls are usually solid without a damp proof course. Lime mortar is softer and weaker than stone, brick or cob therefore it is able to withstand a certain amount of movement (without cracking) that comes with settlement and seasonal changes in ground conditions. Lime mortar is porous and allows moisture to freely evaporate. It is this permeability that is sometimes referred to as ‘walls being allowed to breathe’. Lime mortar helps to keep a building dry inside.