Masonry facades
At a glance
Since the early part of the 20th century, the advent of steel framed structures has resulted in the progressive reduction in weight of the external envelope. Masonry veneers are now much thinner (half brick instead of one or one and a half brick) or in some cases even thinner. The changes have resulted in facade design that is intolerant of movement or moisture and that requires high levels of workmanship to achieve effective performance. See the Introduction.
External brickwork falls into pervious or impervious categories, generally speaking impervious types are more prone to serious leakage as a result of water running down a facade than pervious types, which are able to absorb a certain amount of water and allow it to evaporate out over time. Walls constructed with dense, well burnt bricks demand a high attention to cavity tray detailing. See Water penetration.
In cavity work, cavity trays must be designed carefully and not left to chance. The design and installation must be treated with respect if water damage is to be avoided. Proper bedding, lap and stop end details must be provided, and trays installed at every point where the cavity is interrupted. Tray detailing should be as effective and meticulous as roof detailing. See Cavity construction.
Movement in brickwork can be the result of moisture and or temperature changes, chemical problems (such as sulphate attack), structural movement (such as shrinkage of a concrete frame) or applied loadings. See Movement in masonry.
Cracking will usually occur in a direction that is perpendicular to the forces applied. Diagonal cracking is often (but not necessarily) indicative of structural movements whilst vertical cracking is often related to shrinkage or expansion.
Clay brickwork undergoes an initial irreversible expansion after laying, followed by reversible temperature and moisture changes. Concrete and calcium silicate bricks have a certain irreversible shrinkage after laying.
When used in conjunction with framed construction, care needs to be taken to ensure that adequate provision from frame shrinkage is allowed. Shrinkage of the frame due to long-term creep is a problem with reinforced concrete and timber structures; less so with steel. See Corrosion of metalwork.
It has been estimated that the long-term creep of a reinforced concrete framed building can be as much as 3mm per storey height. See Changes in loading or structural effects.
See also Crack patterns and symptoms.
Other considerations are: