The durability of a wall is indicated by the frequency and extent of the
work necessary to maintain minimum functional requirements and an
acceptable appearance. Where there are agreed minimum functional requirements such as exclusion of rain and thermal properties, the durability of walls may be compared through the cost of maintenance over a number of years. Standards of acceptable appearance may vary widely from person to person, particularly with unfamiliar wall surface materials such as glass and plastic coated sheeting, so that it is difficult to establish even broadly-based comparative standards of acceptable appearance. With the traditional wall materials there is a generally accepted view that a wall built of sound, well burned bricks or wisely chosen stone ‘looks good’ so that there is to a considerable extent a consensus of acceptable appearance for the traditional walling materials.
A wall built with sound, well burned bricks laid in a mortar of roughly the same density as the bricks and designed with due regard to the exposure of the wall to driving rain, and with sensible provisions of dpcs to walls around openings and to parapets and chimneys, should be durable for the anticipated life of the majority of buildings and require little if any maintenance and repair. In time, these materials exposed to wind and rain will slowly change colour. This imperceptible change will take place over many years and is described as weathering, that is a change of colour due to exposure to weather. It is generally accepted that this change enhances the appearance of brick and stone walls.
Walls built of brick laid in lime mortar may in time need repointing, to protect the mortar joints and maintain resistance to rain penetration and to improve the appearance of the wall.