Why use traditional methods and materials?
Modern building techniques began to be introduced in the second half of the 19th century. Cement-based mortars, renders and plasters came into general use during the late 1940's. Modern techniques rely on impervious outer layers, cavity walls and barriers against moisture. Such systems are incompatible with the traditional solid walls of period properties. This is why it is so important to use traditional methods and materials on older buildings.
Old buildings need to breathe and be able to release moisture. This is why we use lime mortar for re-pointing and rendering. Lime is soft and porous and has the ability to absorb and then release moisture back into the atmosphere, rather than trapping and drawing dampness back into the building or forcing it out through the masonry (spalling). Cement pointing, water proof sealants, damp proof membranes and even insulation materials can act as a barrier to the buildings natural ability to breathe.
Old buildings will retain their original character when finished in lime.