Wall ties connect the inner and outer leaves of a cavity wall. Older mild-steel ties can corrode and expand, while other ties may be missing, loose or poorly installed. Horizontal cracking can be a warning sign, but it is not proof: a targeted survey is needed before repair is specified.
When this guide fits
Clues worth recording
- Horizontal cracks following mortar joints
- Bowing or rippling in an outer wall
- Cracks to render or around openings
- A survey or valuation flagging suspected corrosion
What wall ties do
A cavity wall has two separate leaves of masonry. Wall ties span the cavity and transfer lateral loads so the leaves act safely together. The tie itself is concealed, which is why surface symptoms and a normal visual survey can only take the diagnosis so far.
Why ties can fail
In older properties, unprotected or lightly protected mild steel can corrode in a damp cavity. Rust occupies more space than the original steel and can force apart the mortar bed. Ties may also be too sparse, incorrectly embedded or affected by later alterations.
- Age and original tie type
- Moisture exposure and mortar condition
- Coastal or exposed location
- Installation quality and later building work
What a proper investigation looks like
A competent specialist should review the wall pattern and crack direction, check plumb and movement, locate representative ties and inspect the cavity at selected points. Findings should connect evidence to recommendations—not jump straight from one crack to replacement.
Do not authorise whole-house tie replacement from a photograph or sales visit alone.
If replacement is recommended
A repair design normally specifies the new tie system, spacing, substrate suitability and treatment of existing ties where necessary. Cracks or damaged mortar may need separate repair. Ask for the written scope, limitations and guarantee terms before choosing a contractor.
Questions homeowners ask
What people usually want to know
Does horizontal cracking always mean wall tie failure?
No. It is a recognised possible indicator, but thermal movement, lintel problems and other masonry defects can create similar patterns. Diagnosis should be based on inspection.
Can a normal home survey see the wall ties?
Usually not directly. A home survey may flag symptoms and recommend a specialist inspection. Representative ties are commonly located and viewed using specialist equipment.
Is wall tie failure urgent?
Visible bulging, loose masonry or rapid movement needs prompt professional attention. A historic hairline crack without movement may be less urgent, but should still be assessed if wall ties are suspected.
Sources & review
Evidence behind this guide
Reviewed 1 September 2026. We use primary guidance where available and label trade-body advice clearly.