A cavity wall has two leaves of masonry connected by ties. The ties help the leaves act together and transfer lateral loads. Some older metal ties were inadequately protected and can corrode. Expansion may disturb mortar joints, while severe loss of section can reduce restraint. The issue varies by tie type, exposure and construction.
Horizontal cracking is often associated with wall-tie corrosion, but it is not conclusive. Thermal movement, embedded metalwork, structural movement and render defects can produce similar patterns. A home survey identifies visible warning signs and construction risk; it cannot see most ties inside the cavity without a targeted inspection.
Possible warning signs
Regular horizontal cracks following bed joints, outward bulging, displaced masonry and lifting around openings may increase concern. Rust staining is less common because ties are concealed. The absence of cracking does not guarantee that every tie is sound, particularly where render or paint hides the masonry.
Age is only a clue
Early cavity walls may contain ungalvanised or lightly protected ties, but construction dates and practices overlap. Later repairs may have introduced replacement ties. Wall thickness, brick bond and exposure help identify the likely construction, though documentary records or a specialist inspection may be needed to confirm it.
Survey scope and limitations
The surveyor views accessible elevations and looks for crack pattern, distortion and related defects. Standard inspection does not drill the wall, use a borescope or locate and test ties. High walls, render, insulation and adjoining property can significantly restrict the assessment. Those limitations should be reflected in the report's level of caution.
Targeted investigation
Where risk is material, an experienced specialist can locate representative ties, inspect the cavity with a borescope and assess corrosion and spacing. The investigation should sample enough locations to address the concern and distinguish tie defects from other movement. A contractor selling replacement systems should still provide evidence supporting the proposed scope.
Repairs and related defects
Replacement or supplementary ties may be appropriate after diagnosis, alongside local masonry repair. Cracks and bulges should not simply be repointed before the cause is established. Water penetration, failed pointing and cavity insulation may also require attention, but no blanket treatment suits every wall.
The repair design should identify tie type, spacing, fixing substrate and treatment of redundant corroding ties. Work around openings and exposed elevations may differ from sheltered areas. After repairs, displaced masonry and joints still need suitable making good. Retain installation records and photographs because the new ties will become concealed again. Where scaffolding is needed, use the access to inspect flashings, gutters and high-level masonry so related water defects are not left untreated.
- Confirm the wall construction before drilling
- Use representative inspection locations
- Separate tie evidence from other movement causes
- Record replacement work for future owners
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Authoritative sources and further reading
The guide is general information, not property-specific, structural, legal, tax or financial advice. Source pages can change; consult the relevant professional for your circumstances.