Wall tie treatment and cavity cleaning to 1950s semi-detached house to provide a structural repair for rusting wall ties and DPC issues.
The subject building was a conventional 1950s cavity-built semi-detached house.
Problem – corroded de-laminated wall ties
An AWT investigation with a metal detector and an endoscope revealed that the wall ties to the front, right side and rear elevations were galvanised mild steel vertical twist ties, all in a similar heavily corroded condition, showing signs of de-laminating.
Side gable wall:
This had a significant bulge at first floor level from the front to the window. This area required the external skin to be carefully dismantled and rebuilt.
Corroding wall ties were clearly visible. The internal walls at ground floor level were also found to be damp.
Corrosion of the embedded mild steel wall ties had resulted in the forming of ferrous oxide, which had expanded the metal to many times its original thickness, lifting and cracking the brickwork. It was considered likely that the lateral movement noted was due to the absence of effective wall ties.
Bridging of cavities at DPC:
Our investigation revealed that the building had areas within the cavity that were blocked with decayed mortar that bridged the DPC.
Discussion
Wall ties:
AWT’s opinion, based on the Building Research Establishment (BRE)’s recommendations, was that the symptoms/defects noted were consistent on all elevations requiring remedial work. It was considered that the building would benefit from remedial wall tie replacement and the isolation of the existing ties.
Bridging of cavities at DPC:
The bridging of the DPC had rendered it ineffective and could result in rising damp.
Solution – remedial wall tie replacement
AWT completed a remedial scheme providing a viable repair by introducing remedial wall ties, isolating the existing ties and cavity cleaning.
Wall tie treatment:
AWT operatives completed remedial wall tie treatments to the front, right side and rear elevations in accordance with AWT’s Wall Tie Treatment – Generic Repair.
Cavity cleaning:
We cleaned the cavities to the ground floor DPC at the front, right side and rear elevations in accordance with our specifications and AWT’s methods. This meant the removal of sufficient external brickwork to enable the removal of discarded mortar debris, leaving the cavity clear to below the DPC while at all times maintaining the integrity of the wall.
Action Wall Ties (AWT) are the South East specialists in wall tie replacement, 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.
Bulging Brickwork and Brick Slips on 60s /70s Apartment Blocks
Concrete frame blocks of social housing in Wandsworth, London with clearly visible bowing to the brickwork and infill brick slip. Defective support to infill wall with cracked and detached brick slips.
The Structural Problem
The structural survey report on this South West London social housing block
The survey of these circa 1960s/1970s blocks of flats revealed, that due to a construction defect, the external brickwork had insufficient support. AWT also found heavily corroded wall ties plus a lack of weep vents and no horizontal expansion joints.
The infill wall external brickwork was originally only supported onto the concrete floor beam by less than 50mm. Where the wall had bulged outward this was reducing the support to just 30mm with the loads onto the brick-slips causing them to bulge out.
Our Structural Repair Solution
The infill wall brickwork was leaning and in danger of becoming detached. AWT promptly made the elevation floor safe (erecting a scaffold to provide access) by installing AWT’s specially developed props.
The remedial work included:
Installation of stainless steel support angles and cavity trays
Clearing debris from the wall cavities
Rebuilding the brickwork by removal, re-bedding and fixing of brick slips
Installation of stainless steel wall ties
Provision of horizontal expansion joints.
Repair and Replacement of Brick Slips
The original bricks and brick slips were reused when possible. Replacement bricks, mortar and sealants were colour matched to maintain the visual integrity of the apartment blocks.
Action Wall Ties are the apartment block structural repair specialists. Our brick slip and wall tie replacement solutions are available to clients in the South East i.e. in London & in Kent, Sussex, Surrey & Essex.
Action Wall Ties (AWT) are specialists in structural repairs to concrete framed buildings and tower blocks. From movement issues to wall tie replacement and brick slip repairs. We provide specialist professional solutions to a wide variety of structural problems. Contact us on 01227 721 255, or email us.
