What Are Cavity Wall Ties?
Cavity wall ties, such as fishtail ties made of iron or steel, play a crucial role in construction by connecting the inner and outer walls of a cavity wall. Beginning in the early 1920s, the innovation of the Butterfly tie, crafted from twisted wire, emerged as an alternative.
Positioned horizontally within the wall cavity and secured with mortar, these ties fortify the structure by preventing moisture from traversing from the exterior to the interior wall. Their strategic design is integral to ensuring the safety and stability of the wall. In the absence of proper wall ties, or if they become corroded over time, substantial sections of brickwork—such as gables—can succumb to the forces of wind suction, leading to potential collapse.
What Causes Wall Ties To Corrode?
Wall ties are an essential component of cavity wall construction, connecting the outer and inner leaves of masonry and helping to maintain the structural stability of a property. While designed to last for many years, wall ties can deteriorate over time, particularly in older buildings where less durable materials were used.
Moisture and Corrosion
The most common cause of wall tie failure is corrosion. Traditional mild steel wall ties are vulnerable to rust when exposed to moisture within the cavity. As steel corrodes, it expands significantly, placing pressure on the surrounding mortar and brickwork. This expansion can lead to horizontal cracking in mortar joints, bulging walls, and, in severe cases, structural instability.
The Impact of Black Ash Mortar
One of the main factors associated with accelerated wall tie corrosion in older properties is the use of black ash mortar. Widely used in many parts of the UK during the early and mid-20th century, black ash mortar was produced using waste materials from coal-fired furnaces and industrial processes.
Unfortunately, black ash mortar often contains impurities such as sulphates, chlorides, and unburnt carbon. These contaminants can create a more aggressive environment around metal wall ties, increasing the rate of corrosion. When moisture enters the masonry, these soluble salts can be activated, further accelerating the deterioration of embedded steel components.
Age and Original Materials
Many properties built before the 1980s contain galvanised or unprotected steel wall ties that were not manufactured to modern durability standards. Over decades of exposure to moisture and environmental conditions, the protective coatings can fail, leaving the steel vulnerable to corrosion.
Exposure to Severe Weather
Properties located in coastal areas or regions exposed to driving rain may experience higher levels of moisture penetration within cavity walls. Salt-laden air and persistent damp conditions can significantly increase the risk of wall tie corrosion, particularly where older wall ties are present.
Why a Wall Tie Survey is Important
Corroded wall ties are hidden within the cavity and often cannot be assessed through a simple visual inspection. A specialist wall tie survey uses borescope equipment to inspect the condition of existing wall ties, identify any signs of corrosion or failure, and determine whether remedial work is required.
Early detection can help prevent more extensive structural issues and ensure that any necessary repairs are carried out before significant damage occurs.
Horizontal Cracking
Horizontal cracks usually appear in the mortar joints and are commonly caused by the expansion of corroding wall ties. As the steel rusts, it expands and forces the surrounding masonry apart.
Bulging Masonry
Bulging or bowing walls occur when wall ties fail and no longer restrain the outer leaf. In severe cases, this can lead to instability and potential collapse if left untreated.
Window / Door Opening Distortion
Gaps or distortion around windows and doors can occur when the wall loses stability. Failed ties allow movement, which puts pressure on openings and causes misalignment.
Stepped Cracking
Stepped cracking follows the mortar joints in a stair-step pattern. This is a strong indication of wall tie failure, where expansion or movement is transferring stress through the brickwork.
Cavity Wall Tie Survey
If you suspect issues with cavity wall tie failure, or require confirmation for a property transaction, it’s essential to instruct a specialist surveyor. We provide comprehensive cavity wall tie surveys designed specifically to support homeowners, buyers, sellers, and mortgage lenders.
Our reports are fully mortgage-ready, making them suitable for submission to lenders and solicitors. They are among the most detailed on the market, combining technical accuracy with clear, structured findings—delivered with a fast turnaround to keep your transaction moving.
Our expert surveyors carry out thorough inspections in accordance with recognised industry standards. Using advanced diagnostic equipment, including endoscopes and metal detection tools, we assess the condition of wall ties, identify defects within the cavity, and highlight any associated cracking or movement in the masonry.
To ensure complete objectivity, we grade all wall ties in line with BRE Digest guidance and established chart criteria. This removes subjectivity from the process—our recommendations are based on proven industry data rather than opinion, giving lenders and clients confidence in the findings.
Following the survey, you will receive a clear, professional report outlining the condition of the wall ties, supported by photographic evidence, grading, and, where necessary, recommendations for remedial work along with a detailed quotation.
Get An Instant Survey Quote
Our instant quote tool makes it quick and easy to get a price for your cavity wall inspection report. Simply enter a few basic details, including the property address requiring inspection, and you’ll receive an accurate quote instantly. You can then book your survey online in just a few clicks.
We won’t ask for or store your personal contact details unless you choose to proceed with the booking.
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Why choose Northwest Wall Ties
Family Values: As a family-run business, we understand the importance of trust and reliability. You can count on us to treat your property with the same care and attention to detail as we would our own.
Wall Tie Installers Federation Members: Northwest Wall Ties are members of the Wall Tie Installers Federation, registered installers subscribe to a code of practice based on BRE Digests 329 and 401 and the Federation’s own rules. This membership together with adherence to BRE standards provides reassurance to our customers on the quality of our work.
Expertise: With years of experience in cavity wall tie inspection and repair, we have the knowledge and skills to deliver superior results, no matter the complexity of the project.
Customer Satisfaction: Your satisfaction is our top priority. We go above and beyond to exceed your expectations and ensure a smooth and hassle-free experience from start to finish.
Quality Assurance: We stand behind the quality of our workmanship and materials, ensuring that your property receives the best possible care and attention.
Cavity Wall Tie Survey FAQs
Common questions about cavity wall tie surveys, costs and what to expect.
A cavity wall tie survey is an inspection process that evaluates the condition of the metal ties connecting the inner and outer leaves of a cavity wall. The survey aims to identify any signs of corrosion, failure, or inadequacy in the wall ties, which are crucial for maintaining the structural integrity of the wall. The procedure typically involves:
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An external appraisal of the building to identify construction details, the presence of a cavity, insulation, and any visible cracks or defects.
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Using a metal detector to locate wall ties.
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Drilling small inspection holes near the ties and employing a borescope to visually assess their condition.
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Photographing the ties for further analysis and record-keeping.
This process is straightforward and usually takes less than an hour.
Cavity wall ties play a crucial role in construction by connecting the inner and outer walls of a cavity wall. Positioned horizontally within the wall cavity and secured with mortar, these ties fortify the structure by preventing moisture from traversing from the exterior to the interior wall. Their strategic design is integral to ensuring the safety and stability of the wall. In the absence of proper wall ties, or if they become corroded over time, substantial sections of brickwork—such as gables—can succumb to the forces of wind suction, leading to potential collapse.
Cavity wall ties, initially made from iron or steel, are prone to corrosion in damp conditions. To prevent this, they were galvanized with zinc. However, this protective layer can degrade over time, leading to failure. Pre-1981 wall ties often fail prematurely due to various factors such as corrosive mortars, exposure to rain, and substandard galvanizing. Fishtail wall ties expand upon corrosion, causing cracks in the outer leaf, while Wire Butterfly ties may snap without expansion, resulting in wall bulges. Replacement of older wall ties with modern stainless steel ones is recommended to prevent future failures.
Signs of cavity wall tie failure include:
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Horizontal Cracks: Found in the mortar, often at a high level, caused by the expansion of corroded wall ties on the external leaf.
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Bulging Brickwork: Indicates snapped wall ties, which can make your property unstable.
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Internal Cracking: Caused by the expansion of corroded wall ties.
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Cracks in the Render: Vertical cracks in the render.
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Roof Edges Lifting: The inner leaf carries the roof load, but as corroded wall ties expand and crack the mortar, the outer leaf takes the load, resulting in forcing the roof upwards or the gable ridge to rise.
If you observe any of these signs, it’s essential to consult a specialist for a comprehensive survey.
A cavity wall tie survey involves several steps:
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External Assessment: The surveyor examines the building’s exterior to identify construction details, the presence of a cavity, insulation, and any visible cracks or defects.
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Locating Wall Ties: A metal detector is used to find the positions of the wall ties.
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Inspection: Small inspection holes are drilled near the located ties, and a borescope (a type of endoscope) is used to visually assess their condition.
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Documentation: Photographs of the wall ties are taken for further analysis and record-keeping.
This procedure is straightforward and usually takes less than an hour.
If a survey reveals that wall ties are corroded or failing, replacement is typically recommended to maintain the structural integrity of the building. The process involves:
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Locating Existing Ties: Identifying the positions of the old wall ties.
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Installing New Ties: New stainless steel mechanical or resin-bonded ties are installed in an offset pattern to the existing ones.
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Isolating Old Ties: The old ties are isolated by removing the surrounding mortar or by using grease-filled sleeves over the exposed ends to prevent further corrosion and expansion.
The work is carried out from scaffolding or temporary scaffold towers, depending on terrain and access. Stainless steel wall ties are used as they are corrosion-resistant. Replacement cavity wall ties also benefit from long-term guarantees.
The frequency of inspections depends on the age and condition of the property. For properties built before 1981, especially those in exposed or coastal areas, regular inspections are advisable due to the higher risk of wall tie corrosion. If you notice any signs of wall tie failure, such as horizontal cracking or bulging brickwork, it’s essential to arrange a survey promptly.