Twelve storey concrete frame building with failing concrete support toes – install stainless steel angles reinforcement and re-tie infill walls
The subject of this case study was a 12-storey concrete frame building with brick infill walls believed to have been constructed in the 1960s.
Problem: Cracks and failing concrete toes/wall ties
The building was of a concrete frame and floor construction, with cavity brickwork infill walls. The infill walls were constructed with an external brick skin on a single course high concrete toe that was visible above the fenestration openings and balcony soffit.
a. Cracking movement was noted to the infill walls.
b. Sections of the concrete toes were found to be failing, along with sections of the external brickwork not supported by the concrete toe.
c. A wall tie deficiency was evident.
Solution – Concrete Repair
AWT completed a remedial scheme, providing a viable repair by the introduction of 10mm stainless steel reinforcement to the concrete toe, remedial wall ties and general brick repairs. Establishing our reputation as a quality concrete repair company.
Making good and pointing: AWT operatives are highly skilled in traditional building methods and always attempt to match replacement bricks, pointing styles and mortar colour to be sympathetic with the existing building.
Action Wall Ties (AWT) are a specialist concrete repair company, working with concrete, and offering masonry reinforcement and repair, providing professional solutions to a wide variety of structural problems. Contact us on 01227 721 255, or email us to discuss your concrete and masonry cracks and issues for a quote and simple quick and reliable solution.
This overview of the history of cavity walls looks at how the use of cavity walls started. It also looks at some of the problems that property owners need to be aware of and how AWT can help to solve these issues. Read on to find out about:
Development of Cavity Wall Construction
Wall Tie Corrosion
Wall Tie Life Expectancy
Wall Tie Damage by Corrosion
Modern Wall Ties
Masonry Damage from Corroded Wall Ties
Cracked Bricks from Failing Wall Ties
Development of Cavity Wall Construction
Cavity wall construction has almost entirely replaced solid wall construction in the United Kingdom. It evolved in the latter years of the nineteenth century and became common in dwellings in northern and western Britain in the early 1900s.
Its widespread adoption as virtually standard in the construction industry happened throughout the building booms of the 1920s, ‘30s and ‘40s.
The gallery above shows the typical outer leaf (the external brickwork) of a cavity wall and the type of damage often associated with failing cavity wall ties.
When identifying whether a wall is of solid or cavity construction, something to be aware of is that the presence of headers in the brickwork (bricks laid with the smallest side facing out) is not always indicative of solid brickwork.
From the mid-1940s to the mid-1950s, “snapped headers” were often used in cavity wall construction to emulate the English bond brickwork pattern that was common in solid brickwork.
Action Wall Ties can help identify whether your property has cavity walls or solid brickwork and diagnose the underlying cause of structural defects.
In the early years, the skins of these cavity walls were held together by metal ties made from cast or wrought iron, mild steel or copper.
Wall Tie Corrosion
The corrosion of wall ties was first officially recognised in the 1960s in South Wales. At first, it was thought to be due to a combination of poor tie protection and exposure to the elements. Time has shown that many of the early ties and mortars were just more susceptible to corrosion.
Mild steel ties initially were either left unprotected or given a bitumen coating, but in the early 1930s zinc coatings or galvanising became accepted.
The most common type of mild steel ties (under BS 1234) are strip ties (commonly known as vertical twist or fishtail) and wire ties (commonly known as butterfly or double triangle). The photo shows a range of traditional wall ties, all of which are prone to corrode and fail over time. In contrast, modern wall ties are carefully designed for strength and durability.
Wall Tie Life Expectancy
It is very difficult to predict the life expectancy of ties used in the construction of houses before 1945.
However, it can be fairly accurately predicted for those built between 1945 and 1964 :
Strip ties will probably last somewhere between 31 and 61 years
Wire ties will probably last somewhere between 15 and 31 years.
The expected life of ties used in construction between 1964 and 1981 is estimated at:
23 to 46 years for strip ties
13 to 26 years for wire ties.
ALL mild steel wall ties will eventually corrode – the only question is when!
As shown in the photo, Action Wall Ties can survey cavity wall ties by drilling small inspection holes and using an endoscopic camera to assess the wall ties. Contact us to arrange a wall tie survey.
Wall Tie Damage by Corrosion
The key here is catching the problem as early as possible. If the symptoms are recognised before deterioration has progressed too far, the walls may be re-stabilised rather than needing to be re-built.
Old ties must be located using an electronic detector and replaced with a suitable corrosion-resistant remedial fixing.
Finally, existing ties will need to be isolated to prevent further damage to the outer leaf of brickwork. Corrosion of a tie within the inner leaf of a cavity wall is unlikely to become significant as they are embedded in a dry environment.
AWT’s specialist equipment allows them to isolate failing wall ties and install remedial wall ties with minimal disruption by working from the outside of the building.
Ferrous oxide (rust) will result when embedded mild steel wall ties corrode. This will expand to several times the thickness of the metal it has resulted from, often breaking through the outer leaf of the brickwork (sometimes splitting the bed joints) and causing either lifting or bowing of the walls and damage to internal finishes.
Rust Damaged Wall Tie
Rusty Wall Ties
Failed Wall Tie
Crumbling Wall Ties
Rusted Wall Tie
Corroded Wall Ties
From a structural perspective, this leaves the wall vulnerable to vertical and wind loads, especially in the case of large gable and unreturned walls. The instability of the wall will eventually result in the ties corroding away completely, necessitating the rebuilding of the wall. The gallery shows how corrosion causes the cavity wall ties to lose strength and eventually crumble away.
Modern Wall Ties
As shown below, Action Wall Ties uses a range of modern cavity wall ties that are far superior to traditional wall ties. Using their many years of experience, AWT selects the most appropriate remedial wall tie style for each project.
There are 3 main types of replacement wall ties:
Mechanical
Helical
Resin or grout bonded
All AWT’s replacement wall ties are made from high-grade stainless steel. They are designed to restore structural integrity and provide a long lasting solution to cavity wall tie issues.
Equipment designed by AWT can also realign brickwork that is bulging and bowing due to failing wall ties before installing new wall ties and lateral restraints.
Kent based Action Wall Ties (AWT) are specialists in wall tie surveys and replacement, providing professional solutions to a wide variety of cavity wall problems. We serve domestic and commercial customers, local authorities, housing associations and insurance companies across London, Kent, Essex, Sussex and Surrey.
