Wall tie failure

Wall tie failure is when the metal ties linking the two leaves of a cavity wall corrode and stop holding them together, letting the outer leaf crack, bulge or lose stability. The usual sign is horizontal cracking in the mortar every few courses, and the fix is a survey followed by new remedial ties, with old ties isolated or removed where needed.

What are cavity wall ties?

Cavity wall ties are metal connectors built into the mortar joints of a cavity wall to hold the inner and outer leaves together. They let the two leaves share wind loads and stop the thinner outer leaf acting on its own. In many older cavity walls the ties are steel, protected by a zinc coating that slowly wears away. Once the steel rusts, it can expand in the mortar and lift the brickwork, or thin until it snaps and no longer restrains the wall.

What are the signs of wall tie failure?

The classic sign of wall tie failure is horizontal cracking in the mortar joints, repeating at regular heights up the wall, often around every sixth course where the ties sit. Expanding rust lifts the outer leaf, so the wall can grow slightly taller and push up at the eaves or window heads. Not every failing tie shows, though. Thin wire ties can corrode and snap without expanding much, leaving the outer leaf poorly restrained with few visible signs.

• Horizontal cracks repeating every few courses
• Bulging or bowing outer brickwork
• Lifting at the eaves or verges
• Distorted window or door openings
• Horizontal lines of cracking in render

Which houses are most at risk?

Houses with cavity walls built before the early 1980s are most at risk, because many have steel ties with thinner zinc coatings than later ties. Exposure speeds corrosion: walls facing driving rain, houses near the coast and walls built with black ash or other aggressive mortars tend to fail sooner. Solid-walled houses, common before cavity walls became usual, have no cavity ties, though they can have bonding problems of their own. A survey confirms what type of tie your walls actually have.

How is wall tie failure surveyed?

A wall tie survey usually starts with a visual inspection, then a metal detector to locate the ties and a borescope, a small camera pushed through a drilled hole, to see them inside the cavity. A brick may be removed here and there to inspect ties directly. The surveyor records the tie type, how far corrosion has gone and whether the outer leaf has moved. That shows whether replacement is needed, whether old ties must be isolated or removed, and whether any brickwork needs rebuilding.

How are wall ties replaced?

Wall ties are replaced by drilling through the outer leaf and fixing new stainless steel remedial ties into the inner leaf, mechanically or with resin, at a spacing set by the survey. The holes are filled and pointed to match. Where the old ties are expanding and lifting the brickwork, they are usually cut out or isolated so they cannot do more damage. For a semi-detached house the work usually takes 2 to 3 days. Severely displaced brickwork may need taking down and rebuilding.

How much does wall tie replacement cost?

Wall tie replacement for a semi-detached house is a guide £2,500 to £5,000 inc VAT. A mid-terrace house is about £1,800 to £3,500, and a detached house about £3,500 to £7,000. Scaffolding, where needed, adds about £600 to £1,800 per elevation, and rebuilding sections of bulging brickwork is priced on top. These are guide prices that vary by region and access, and they are confirmed in writing after a survey, once the number of ties and the access are known.

Is wall tie failure covered by insurance?

Wall tie failure is usually treated as gradual deterioration rather than an insured event, so buildings policies often do not cover it. It is sometimes mistaken for subsidence, because both crack walls, but the patterns differ: tie failure gives lines of horizontal cracks, while subsidence tends to give diagonal ones. If you are not sure which you have, get the wall inspected, and if subsidence is possible, tell your insurer before permanent repairs start. Your policy wording sets out what is covered.

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