Buildings with cavity walls started in the late nineteenth century and became much more popular during interwar. The energy crisis brought the change of building regulations, which meant that insulated cavities became a common thing in and after the 1970s.
Early cavity walls were connected with brick headers or stones, which were later replaced with cast or wrought iron. In some cases these were dipped in tar and sand before installation to give some protection. Later these were again replaced with galvanised mild steel ties. All of these ties were sensitive to corrosion when in damp conditions especially in walls built with mortar containing ash.
These days, corroded cavity ties are a common problem with the cavity wall properties. Corrosion can cause metals to expand several times its original thickness. This can cause cracking, bulging or instability of walls, and in worst case scenario, a collapse.
There are a few ways of dealing with corrosion of failed ties and it depends on the severity of corrosion and other external conditions.
In order to retain the stability of the walls, new ties can be installed. There are several different types of ties that can be installed retrospectively. These could be resin fixed, mechanically or helical ties.
The use of a certain type of retro ties will depend on wall construction, condition of the wall, presence and type of cavity insulation and other factors. Often, just installation of new ties may not be enough to fix the problem. The existing corroded ties may also require removal or at least isolation to prevent further damage to the wall.
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