Cavity wall structures have been a mainstay of British construction since the 1930s. Cavity walls replaced solid masonry walls in many cases, aiming to improve insulation and reduce damp within properties.
The lynchpin of this method is the cavity wall tie, which provides structural stability to both sides of a cavity wall. When a wall tie fails, this can caused increased movement in either side of the wall, which leads to structural cracks and bowing.
In this blog, you’ll learn how wall tie failure causes cracking and instability, the warning signs to look for, and how professional wall tie repairs can protect your home.
What Wall Ties Do (And Why Your Home Depends on Them)
A cavity wall is made up of two walls (or leaves) with a gap in between. This provides an additional layer of insulation against both cold and damp, making the property more pleasant to live in.
An essential component in a cavity wall is wall ties. These metal ties are installed between the two leaves, connecting them together. The interior wall is often the load-bearing wall, and by anchoring both leaves together, the inner wall provides additional stability to the outer wall.
However, wall ties are not indestructible, and when they become damaged or corroded, the failures can spread throughout the entire wall, not just the individual bricks where the wall ties are installed.
Why Wall Ties Fail in UK Properties
Wall ties can fail in UK properties for several reasons.
Corrosion of Older Mild Steel Ties
Originally, cavity wall ties were made from galvanized or bitumen-coated steel. These were used originally due to their strength. However, they are now known to corrode despite the preventative coatings. Corroded wall ties can lead to structural issues such as cracking as the wall ties lose their integrity.
Mortar Moisture and Rust Expansion
Similarly, moisture from a defect or rising damp can enter the exterior wall. This moisture then enters the porous mortar, causing it to weaken and allow the tie to come loose. Similarly, it can also cause the wall ties themselves to rust, reducing their structural strength, as well as expand in the mortar joint, loosening them from the wall.
Age of Property
Age is also a consideration in cavity walls and wall ties. Walls can fall victim to weathering or spalling over time, and older constructions do not benefit from the same weatherproofing and modern materials that new-build constructions do.
Poor Installation or Unsuitable Tie Types
Installing insufficient wall ties or installing them incorrectly can also adversely affect the integrity of the final wall. Weaker wall ties will not be able to properly support both walls, while installing them incorrectly can lead to the exterior wall bowing or sagging outward.
The Early Symptoms of Wall Tie Failure Most Homeowners Miss
You can look out for the following wall tie damage symptoms during your regular property checks;
- Horizontal cracking in the mortar joints of either wall.
- Stepped cracks in brickwork, especially cracks going through bricks. The same pattern might be mirrored on both the exterior and interior walls.
- Bulging or bowing external walls
- Rust staining on brickwork from corroding wall ties
- Gaps forming between bricks and mortar.
How Wall Tie Failure Causes Structural Wall Movement
When a wall tie corrodes from contact with moisture, iron oxide (rust) is formed. This rust takes up a greater surface area, which forces the tie to expand. As the tie expands, the masonry is pushed apart, and the connection between the tie and wall weakens.
Once weakened, the outer leaf of the wall will begin separating from the inner leaf. This structural wall movement first causes cracks to form in the brickwork or mortar, but can lead to building or bowing as the ties continue to corrode and lose their structural strength or become unattached from the wall.
Why Wall Tie Cracks Are Often Mistaken for Subsidence
Homeowners often confuse wall tie cracks with subsidence as their symptoms often overlap. Stepped cracks are a shared symptom of both structural issues, and can lead to misdiagnosis.
Another linked problem is that the issues are often localised to one area. In cases of wall tie failure, this is usually down to a defect feeding moisture into a wall. However, in subsidence the key factor is foundational movement, which can cause cracks to form through an entire elevation.
To diagnose whether an issue is linked to subsidence or wall tie failure, it’s important to look for symptoms unique to each issue, such as rust staining or internal cracking around doors and windows. Our blog on Subsidence and Structural Movement goes into further detail on symptoms you may experience from a structural concern.
How Professionals Diagnose Wall Tie Failure
During a structural repair survey, our surveyors will investigate a property for the likely causes of wall tie failure, and confirm whether a structural issue is down to tie failure or another structural issue. Our companion blog, Cavity Wall Tie Inspection and Replacement, will provide some more detail on some of the steps we’ll cover below.
The first method our surveyors use is to assess the cracks within the wall. They will identify patterns in the cracking, and whether these patterns repeat on both the exterior and interior walls. They will also look for visible bulging within the wall.
Another method our surveyors use to diagnose wall tie failure is through metal detection. Our surveyor will use a metal detector to plot where the wall ties are installed within the wall. This can confirm whether there are enough ties in the wall, as well as if they’re spaced adequately enough to prevent the exterior wall from bowing.
If the crack inspection and metal detection are inconclusive, a borescope inspection can provide additional information. This involves drilling a hole into the cavity wall and then feeding a flexible light-equipped camera through it. This provides the surveyor with visibility of the wall ties and their condition without needing to disassemble sections of the wall. Borescope inspections are considered a non-destructive testing method, as the hole can be refilled upon completion of the survey.
Often, visual checks are not enough to confirm a diagnosis of wall tie failure, and the methods above will help a surveyor to confirm the diagnosis with as little disruption as possible.
What Happens If Wall Tie Failure Is Left Untreated
Leaving a faulty wall tie untreated will allow the issue to persist, and lead to extended damage or even total structural failure of a cavity wall.
In the short term, an exterior wall may show progressive bowing as the wall tie continues to deteriorate. This might also cause the mortar and masonry to crumble.
In the long term, there is a risk that the outer leaf of the wall could collapse completely. This would put the inner leaf at risk of weathering, as well as cause preventable damage to the remaining wall ties.
As with many structural repairs, early diagnosis and treatment leads to a significant reduction in both disruption and costs, and often an earlier repair is significantly easier than a later reconstruction.
How do Wall Tie Replacement Repairs Work?
Should your wall ties need replacing, the repair will be completed in stages. First, our technician will locate each wall tie that needs to be replaced. They will then plan out an offset pattern for the new wall ties, ensuring they are spread out evenly to distribute the strain from the interior wall without causing stress to specific areas of the outer wall.
Next, our technician will drill a 10mm hole through the face of each brick in the pattern. Through each hole, a new stainless steel wall tie is passed until it embeds itself between the inner and outer leaves. This wall tie can then either be tightened mechanically, or bonded to the masonry with a resin compound.
Once tightened or set, the wall can be tested to ensure the wall ties are correctly installed and are holding the weight of the wall as intended. If stable, the old wall ties are isolated, either by removing the mortar around them or by using grease-filled sleeves over the exposed end. The holes can then be repointed to complete the repairs.
Which Properties Are Most at Risk?
There are several types of property that are at risk of developing cavity wall tie issues;
- Older housing stock is particularly vulnerable, due to the use of inadequate materials that are prone to corrosion.
- Coastal areas have an increased risk due to salt corrosion and additional weathering.
- Properties with persistent damp masonry from elevated ground levels, urbanisation, groundwater flooding, or faulty rainwater goods.
If you’ve noticed cracking or bulging brickwork, a specialist inspection can confirm whether wall tie failure is the cause before more serious movement occurs.
FAQs
What are the Signs of Wall Tie Failure?
Wall tie failure can be identified by bowing walls, cracking or gaps forming within or through masonry, and rust staining on the surface of a wall.
Are Corroded Wall Ties Dangerous?
Yes, corroded wall ties can lead to the structural collapse of a cavity wall. This can lead to structural weakness in adjoining areas of the property that could endanger the health of a property’s inhabitants.
Can Wall Tie Failure be Repaired?
Yes, wall tie failure can easily be repaired by installing new wall ties into the wall and isolating any corroded wall ties to prevent rust expansion from causing new cracks in the mortar.
How Much Does Wall Tie Replacement Cost in the UK?
Wall tie replacement costs vary depending on the size of your property and how many wall ties are required to restore integrity to the wall. We recommend requesting a survey to have your property assessed, which will include a quote to replace any corroded wall ties within your walls.
Is Wall Tie Failure the Same as Subsidence?
No, while both subsidence and wall tie failure cause structural movement, subsidence is caused by movement within the foundation of a property, while wall tie failure causes movement within the cavity wall itself.
