Problem
According to BRE research out of nine million dwellings constructed with cavity walls, two million suffer wall tie corrosion or failure and are in need of specialist remedial wall tie replacement. Often the problem is found to be exacerbated by insufficient ties having been installed during construction.
Causes
Inadequate protection – prior to the 1930s ties were not galvanised.
Substandard galvanising – the British Standard for weight of galvanising was actually reduced between 1964 and 1981.
Chemical action – for instance where corrosive black ash mortar has been used.
Location – such as marine environments with driving rain and salt laden atmospheres.
Symptoms
- Horizontal cracking at regular intervals in external mortar joints.
- Outward bulging of the wall.
- The lifting of roof edges.
- Internal cracks.
