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.
- 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.
- Horizontal cracking at regular intervals in external mortar joints.
- Outward bulging of the wall.
- The lifting of roof edges.
- Internal cracks.
The first step in a repair programme is a survey to determine the extent of the problem.
The position of existing wall ties is plotted using a metal detector and then an endoscope is used to examine their condition. Bricks may have to be removed for the physical examination of sample ties.
Installation of Replacement Ties
A range of alternative wall tie designs is available – resin, mechanical or cementitious -depending on the type and condition of the masonry involved. In most cases the existing ties are isolated to prevent further corrosion.
Formed in austenitic stainless steel, replacement ties are available in differing lengths to suit cavity widths up to 110mm. All designs incorporate a centre drip to prevent transmission of water across the cavity.