14-storey concrete frame block with bowing brickwork
A 14-storey concrete frame block with bowing brickwork and brick slip failing – re-tie, brick slip fixing, introduction of remedial expansion joints
The subject building was a 14-storey block of residential apartments, believed to have been constructed in the 1960s.
Problem with the brick slips
The building was of concrete frame construction. Cavity infill walls with two rows of brick slips concealed the concrete floors, forming the appearance of continuous brickwork.
The infill brickwork walls consisted of an external skin of half-brick thick stock bricks with a 60mm cavity and an internal skin of 100mm solid clinker rich blocks. The concrete floor slab was in line with the head of the window and there were two rows of brick slips that became detached from the concrete floor and in many cases had fallen.
Structural Repair Solution
Under the direction of Conisbee’s structural engineers, AWT completed a remedial scheme – which included the replacement and re-bedding of the brick slips and the mechanical fixing to the brick slips, the introduction of remedial ties and remedial expansion joints, and general brick repairs.
Action Wall Ties (AWT) are specialists in masonry reinforcement and repair, providing professional solutions to a wide variety of structural problems including cracked, lifting and falling brick slips on apartment blocks in the London area. Contact us on 01227 721 255, or email us to discuss your brick slip repair options.
13-storey building with bi-metallic wall tie corrosion
Circa 1960/70s 13-storey concrete frame building with bi-metallic corrosion to wall ties – replacement wall ties
The subject building was a circa 1960/70s 13-storey, high-rise block of maisonettes of concrete frame construction with single and two-storey brickwork veneer to the South and North elevations and two-storey inset balconies of fenestrations and cavity infill walls to the East and West elevations.
Structural Problems with walls and brickwork
The cavity infill walls were constructed of good quality multi-red stock bricks externally (all in stretcher bond) with 70-80mm cavity and lightweight blocks internally.
The infill walls were constructed on the inset concrete floor with a bituminous felt DPC cavity tray on the concrete floor. No raked-out perps or weep holes were noted.
The brickwork was found to be generally in good condition, with some signs of cracking and distress noted to the south elevation. The pointing appeared to be of a good standard and had weathered well, with the exception of the brickwork below the windows to the east and west elevations.
Inspection with an Imp wall tie detector and the use of an endoscope to every brickwork panel revealed that the wall ties were vertical twist ties and were located in “Abbey Anchor” dovetail slots cast into the concrete wall.
The vertical twist ties had a fishtail end built into the brickwork and a dovetail end that engaged into the dovetail slots embedded to the concrete wall. The embedded slots appeared to be galvanised and in good condition, with no corrosion noted.
The ties viewed were in poor condition with varying degrees of corrosion noted.
• Loss of section had occurred on the built-in fishtails.
• Laminated corrosion was present on the upper surface.
• No corrosion was noted on the dovetail end.
Discussion
The aggressive localised corrosion was deemed to have been significantly exacerbated by bi-metallic action, with the slot becoming cathodic (positive) and the tie becoming anodic (negative), creating a “corrosion hot spot” fuelled by moisture and oxygen within the bed joint. It was also noted that the underside of the portion of tie within the cavity had not corroded, but the upper section covered in mortar had.
The severity of the corrosion noted was significant, and if left to continue without repair it would most likely result in the opening up of the bed joints and cracking of the wall panels and cost much more to repair.
Some horizontal cracking, lifting and opening up of joints were noted at irregular intervals.
Metal ties were located behind the cracks with an electronic wall tie locator. Some corroded wall ties requiring repair were clearly visible.
Wall Tie Replacement and Repair Solution
AWT completed a remedial scheme providing a viable repair through the introduction of a pattern of remedial wall ties and the isolation of the existing ties, followed by re-pointing.
Action Wall Ties (AWT) are specialists in masonry reinforcement and repair, providing cost effective wall tie replacement and repairs and professional solutions to a wide variety of structural problems in Surrey, London and Kent.
Replacing wall ties are a speciality of ours and we have developed cost effective repair techniques, avoiding more costly repairs if left later down the line, so to discuss these with us please contact us on 01227 721 255, or email us.
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.
Two LPS Blocks, Bow London (Pre-Ronan Point) – AWT remedial panel ties and anchors into the floor beams to the upper floors.
Long Lasting Structural Repairs
AWT completed structural repairs to these two LPS blocks in East London. The work that involved the installation of a remedial panel tie system to the external large sandwich panels and anchors into the floor slab to the upper floors.
The photos above show the buildings 12 years later. The structural repair techniques used by AWT are designed to last.
Some structural repair contractors may offer cheaper quotes because they fail to follow the guidelines provided by the British Standards Institution and the Building Research Establishment Specification Digest. This can seriously impact the structural integrity of a building, especially mid and high rise blocks. Local councils, housing associations and landlords can rely on AWT to provide safe structural repair solutions.
AWT’s team of skilled structural repair specialists are available across London and the South East of England. Action Wall Ties (AWT) are specialists in masonry reinforcement and repair, providing professional solutions to a wide variety of structural problems. Contact us on 01227 721 255, or email us.
Eight-storey 1960s concrete frame building in Aldershot, Hampshire. Cavity cleaning and remedial wall ties.
Cavity Wall Problems
The subject building started as a 1960s eight-storey commercial concrete frame building that was converted to 50 flats in 2004. Dampness, poor insulation and instability to the brickwork flack walls and brickwork features were constantly experienced and reported.
Action Wall Ties was instructed to engage a firm of consulting structural engineers to jointly undertake an intrusive inspection in order to establish a defects report on our findings to enable the design of a suitable remediation.
Concrete Frame Cavity Wall Repairs
Following AWT and Conisbee’s intrusive investigations a remedial scheme was developed that proposed providing temporary support at each floor beam, with AWT developed props, to accommodate the continuous removal of brickwork to clean the cavity and install a cavity tray
This was followed with the reinstatement of the brickwork, together with remedial wall ties and bed joint reinforcement to assist in supporting the brickwork.
Once the intrusive survey has been completed, remedial wall ties were installed and the areas of bridged cavity identified for cleaning to the foot of each infill wall line.
AWT are experts in repairing cavity wall ties and other common defects on high rise concrete frame buildings. We work together with housing associations, councils and structural engineers to find economical and effective solutions.
Kent based AWT serve customers in London and the whole of SE England. Contact us today to see how we can help. Call 01227 721 255 or email us.
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.
