Wall ties are an essential element for the stability of a cavity wall, tying its weather protecting brick façade to the main body of a building. An effective brick tie system transfers static and live loads across the cavity, enabling load-sharing by both inner and outer walls. Typically cavity wall ties are bedded in a mortar bad joint as a building is constructed.
Cavity tie failure can be a consequence of a construction defect; for example where the original 'built-in' cavity wall ties have been omitted, incorrectly fixed or fitted with brick ties that are too short. Alternatively, failure may be a result of a buildings ageing process, whereby wall tie corrosion may have compromised the walls load-sharing capability.
Over time, mortar joints which host the wall ties undergo a chemical change through carbonation. The mortar becomes aggressive to the base steel and its protective coatings, reducing the life expectancy of cavity tie systems to as little as 26 years.
The design life of the building is typically much longer than this period and it therefore follows that at some point a remedial retrofit replacement of the brick ties may be necessary if the stability and load sharing capability of the wall is to be maintained.