Cavity wall ties are concealed metal components that connect the inner and outer leaves of a cavity wall. They provide restraint and help the two leaves act together.
Why can wall ties fail?
In some older properties, particularly those containing early galvanised or inadequately protected ties, prolonged exposure to moisture can cause corrosion. Rust occupies a greater volume than the original metal and can expand within the mortar joint.
What signs might be visible?
Possible indicators include regular horizontal cracking along bed joints, localised lifting of mortar, rust staining and outward distortion or bulging of the outer leaf. These signs are not unique to wall tie failure, so the cause should not be assumed from cracking alone.
How is it investigated?
A survey may identify a pattern that warrants specialist investigation. This can involve locating ties with electronic equipment and inspecting selected ties using a borescope. The spacing, type, condition and embedment of the ties should be considered.
How is it repaired?
Where failure is confirmed, remedial stainless steel ties are usually installed and defective original ties may need to be isolated. Cracked joints and displaced masonry are then repaired. More extensive rebuilding may be necessary where the outer leaf has become unstable.