Cavity Wall Tie Failure: How to Spot It and What It Costs to Fix

What cavity wall ties do

A cavity wall is two leaves of brick or block separated by an air gap of around 50 to 100 mm. The two leaves are tied together by metal wall ties embedded in the mortar joints, typically every 450 to 900 mm horizontally and 450 mm vertically. The ties stop the two leaves moving independently, prevent the outer leaf bowing, and transfer wind loads through the building.

Most homes built between about 1920 and 1980 use cavity walls with mild steel ties. Steel ties corrode over decades when exposed to moisture in the cavity. As they rust, they expand to several times their original thickness, which cracks the surrounding mortar. Eventually the ties fail completely and the wall is no longer tied together.

Tie failure is one of the most widespread structural defects affecting UK housing.

Warning signs

The most reliable visual indicator is horizontal cracking in the mortar joints, typically at regular intervals of 4 to 7 brick courses (matching the tie spacing). The cracks may be:

• Continuous along a wall at one or more levels
• Slightly more pronounced near corners
• Visible as a hairline open joint that runs horizontally across many bricks

Other warning signs include:

• Outer leaf bulging or leaning outwards (visible against a straight edge or in long-shot photos)
• Stepped cracking around windows and doors (less specific to ties)
• Damp patches that appear without an obvious source (corrosion creates voids that admit water)

The risk is highest in homes built between 1945 and 1980 because that period used the thinnest galvanised ties with the least protection. Pre-1945 homes often used heavier wrought iron ties that corrode more slowly. Post-1980 homes use stainless steel or modern galvanised ties that meet current standards and are unlikely to fail.

How surveys identify it

A standard RICS Home Survey Level 2 (HomeBuyer Report) will flag visible horizontal cracking and recommend further investigation. A Level 3 (Building Survey) will go further but rarely involves invasive checks unless the surveyor has a strong concern.

The definitive test is a borescope inspection performed by a specialist contractor. They drill small holes through the mortar joints, inspect the ties with a camera, and report on tie condition, corrosion level, and remaining life. A typical inspection covers several wall sections and costs £300 to £600.

Cost of remedial work

If failure is confirmed, the standard remedy is to install new stainless steel ties to supplement or replace the failed ones. The replacement ties are mechanically fixed and do not rely on mortar bond.

Typical 2026 costs:

• Inspection and report: £300 to £600
• Tie replacement (whole house): £2,000 to £6,000 depending on size and access
• Localised tie replacement (one wall): £500 to £2,000
• Repointing where existing mortar is damaged: £1,500 to £4,000 additional

The work is non-disruptive and does not require leaving the property. There is no need to remove brickwork.

Mortgage and insurance impact

Lenders will sometimes refuse to mortgage a property with confirmed wall tie failure until the work is done, or they may require a retention until the work is completed. Most lenders accept a recently completed remedial scheme with a 20 to 30 year guarantee from a recognised contractor.

Buildings insurance is generally unaffected once the work is done.

What to check before buying

If you are looking at a 1920 to 1980 built cavity wall property:

1. Inspect the external walls for horizontal cracking

2. Get a Level 2 or Level 3 RICS survey

3. If cracking is present, get a specialist borescope inspection before exchange

4. Negotiate the cost of any remedial work off the purchase price

5. Confirm the property's age band on Property Passport UK at [/search](/search) (the platform shows the EPC construction age band sourced from the EPC Register, which is the easiest way to date a property without obtaining a building survey)

Check the property on Property Passport UK before you buy

Property Passport UK aggregates verified data on every one of the 19.35 million properties in England and Wales, including listed building status, conservation area, EPC, flood risk, and HM Land Registry tenure. Search any address at [/search](/search) before you make an offer or commission a survey. Construction-related risks often flag through one of these data points before they show up in the building survey itself.

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