Wall tie failure: the signs and what to do
The classic sign of wall tie failure is a pattern of horizontal cracks in the mortar joints of a cavity wall, repeating at regular heights up the wall. It is a slow problem, but it gets worse with time, and an early survey keeps the repair simple.
What are the signs of wall tie failure?
Wall ties are the metal connectors that hold the two leaves of a cavity wall together. When steel ties corrode, the rust takes up more space than the original metal and pushes the mortar joint apart. Because ties are usually set at regular spacings, the cracks appear at regular heights too, often every five or six courses of brickwork.
Look for the signs below, particularly on the more exposed elevations of the house. One sign on its own is not proof, but two or three together are a strong reason to have the wall checked.
- Horizontal cracks along mortar joints, repeating at similar heights up the wall
- Cracks that are wider on the most exposed side of the house
- The outer leaf bulging or leaning out, often visible when sighting along the wall
- Brickwork at the top of the wall lifting, which can push up the roof edge or open a gap at the eaves
- Cracking at window and door heads, where the outer leaf has expanded against the frames
- Mortar joints that look slightly thicker on one leaf than the other at the reveals
Which London homes are at risk
Wall tie failure only affects cavity walls. Most Victorian and Edwardian terraces in inner London have solid brick walls with no cavity, so they do not have wall ties at all, although they can suffer from different bonding problems.
Cavity walls became common from around the 1920s, so the homes most at risk are the interwar and post-war semis and terraces found across outer London, along with some 1960s and 1970s houses and low-rise flats. Early ties were often galvanised mild steel, and the zinc coating can wear away over the decades, especially where the mortar is porous or contains ash.
Exposure matters too. Walls facing the prevailing wind and rain stay wetter, so their ties corrode faster. Chimneys, gable walls and parapets are often the first places to show problems.
Why failing ties damage the wall
There are two ways ties fail, and they produce different symptoms. In the first, the part of the tie buried in the outer leaf corrodes and expands, lifting and cracking the brickwork as described above. This is the pattern most people notice.
In the second, the tie corrodes through in the cavity and snaps, without much expansion. The outer leaf is then no longer held back by the inner leaf. It may look fine for years, but it has lost much of its resistance to wind and can bulge or, in severe cases, collapse. This type is harder to spot from outside, which is one reason a proper survey is worth doing even when cracking is minor.
Problems that look similar
Horizontal cracking is not always caused by wall ties. Sulphate attack, where sulphates in the bricks react with the cement in damp mortar, also causes mortar joints to expand and crack, often on chimneys, parapets and garden walls. Thermal and moisture movement in long walls, and expansion of some older bricks, can also produce horizontal cracks.
Subsidence usually looks different, with diagonal cracks that are wider at one end and often run through doors and windows. If you are unsure what kind of cracking you have, our guide on whether cracks in your house are serious explains the main patterns and what each tends to mean.
How a wall tie survey works
A wall tie survey confirms whether ties are present, what type they are and how badly they have corroded. The engineer uses a metal detector to locate ties and checks whether the spacing is adequate. At selected points, a small hole is drilled through a mortar joint and an endoscope is passed into the cavity to look at the ties directly.
Where the endoscope cannot show enough, a brick may be removed so a tie can be taken out and inspected along its full length. The survey also notes the mortar type, exposure and the extent of any cracking. Our wall tie condition survey starts from £250 + VAT and gives a clear recommendation on whether, where and how to replace ties.
Repair options
Most wall tie problems are repaired without rebuilding. Remedial ties are installed through the outer leaf into the inner leaf at the spacing set by the engineer. They are usually stainless steel, either helical ties driven or resin-fixed into place, or mechanical ties that expand to grip the masonry.
Where the old ties are expanding and cracking the outer leaf, they may also need to be isolated or removed, otherwise they keep corroding and pushing the brickwork apart even after new ties are installed. Once the wall is secure, cracks are repointed or stitched.
If the outer leaf has bulged badly or lost its bond, sections may need to be taken down and rebuilt with new ties. The engineer specifies the extent and the temporary support needed while the work is done.
- Install remedial stainless steel ties at the specified spacing
- Isolate or remove corroding original ties where they are causing expansion
- Repoint or stitch cracked mortar joints once the wall is secure
- Rebuild badly bulged or detached sections of outer leaf
Buying a house with cavity walls
If you are buying an interwar or post-war house and the survey mentions horizontal cracking, it is worth a closer look before exchange. A wall tie survey is quick and relatively inexpensive, and the result tells you whether you are looking at routine maintenance or a larger repair. Our guide to structural reports for a house purchase explains how to fit this into the conveyancing timetable.
The engineer who signs off our inspection reports is chartered and a Member of the Institution of Civil Engineers (MICE), so you can rely on the findings when you negotiate on price or plan the repair.
Frequently asked questions
Is wall tie failure dangerous?
It develops slowly, so it is rarely an emergency, but it should not be ignored. As ties corrode, the outer leaf loses its connection to the inner leaf and becomes less able to resist wind. In severe cases sections of brickwork can bulge or fall, especially at gables and parapets. Getting the wall surveyed when cracking first appears keeps the repair simpler and safer.
Does my Victorian house have wall ties?
Probably not. Most Victorian and Edwardian houses in London were built with solid walls, usually one and a half or two bricks thick, bonded together with header bricks rather than metal ties. Wall tie failure is therefore uncommon in them. Some later additions, rebuilt walls or extensions may have cavities, so it is still worth checking any area of horizontal cracking.
Is wall tie replacement covered by home insurance?
Usually not. Insurers generally treat wall tie corrosion as gradual deterioration rather than sudden damage, so it falls under maintenance. Policies vary, though, and it is worth checking yours. If wall tie failure has led to a sudden collapse or damage to another part of the house, discuss it with your insurer, but expect the replacement of the ties themselves to be your cost.
Can I just fill the cracks?
Filling the cracks without dealing with the ties hides the problem rather than fixing it. Corroding ties will keep expanding, the cracks will reopen and the outer leaf will continue to lose its connection to the inner leaf. Have the wall surveyed first, install remedial ties where needed, deal with any expanding old ties, and then repoint or repair the cracks.