A substantial 1950s style traditionally built four-storey block of flats typical of London and Kent, with bowing cracking brickwork – remedial expansion joints to solid construction
The subject buildings were substantial 1950s style traditionally built four storey blocks of flats, stepped to accommodate a sloping site.
The Structural Problem
• Visible cracking movement was noted to the front and rear elevations of each building comprising 225mm thick solid brickwork.
• The smaller of the two buildings was constructed with a central step. Cracking in line with the step was noted to the external brickwork, to the rear and to a lesser degree to the front elevations.
• The larger of the two buildings was constructed with two steps. Cracking in line with the steps was noted to the external brickwork to the rear and to a lesser degree to the front.
Discussion
The movement noted was considered attributable to seasonal moisture and the resulting thermal expansion and contraction (i.e. hygrothermal) – a predictable defect, as this large area of brickwork had been constructed without the benefit of any expansion joints.
Solution for Structural repairs
AWT completed a remedial scheme providing a viable repair through the introduction of expansion joints.
1. Flexible joints installed: We introduced crack inducement joints. With a twin diamond bladed saw, we cut a 10mm wide joint, 110mm deep, into the external brickwork between each window and thereafter installed a flexible joint – as indicated with red lines on our proposal images – all in accordance with AWT’s methods.
2. Making good: To the crack line schedule for new joints, we raked out the existing cracked mortar and repaired with new coloured sand and cement mortar to approximately 20mm in depth. 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 specialists in masonry reinforcement and repair, providing professional solutions to a wide variety of structural problems in London and Kent on all types of properties, including Low rise housing blocks. Contact us on Canterbury 01227 721 255, or email us.
Large expanse of brickwork with extensive cracking
Contemporary terrace of houses with large expanse of brickwork with extensive cracking – introducing remedial movement joints and repair the cracking brickwork.
The subject buildings were a terrace of domestic residences of cavity construction, circa 1970s typical of London and Kent.
The Structural Problems
Our inspection revealed many significant cracks to and from windows and to the lower valley of the roofs, along with evidence of many previous repairs. No expansion joints were noted.
Discussion
The cracking noted was not attributable to significant subsidence but to seasonal moisture, thermal expansion and contraction (i.e. hygrothermal).
This considerable length of continuous brickwork had been constructed without the benefit of any expansion joints.
Structural Repair Solution
AWT completed a structural repair / remedial scheme that provided a viable repair by introducing expansion joints, bed joint reinforcement beaming and crack stitching.
With a hydraulic twin diamond bladed saw we cut a 10mm wide joint to the full depth of the external skin and thereafter formed a flexible joint, all in accordance with AWT’s methods.
Action Wall Ties (AWT) are specialists in masonry reinforcement and repair, providing professional solutions to a wide variety of structural problems in London and Kent. Contact us on 01227 721 255, or email us.
Cracking to brickwork façade to 1970s low-rise blocks with short wall returns – install remedial expansion joints
The subject buildings are 1970s low-rise blocks of domestic apartments in North London of conventional brick built construction, featuring a stepped out entrance section leading to a central stairway.
Detailed Case Study:
The buildings are three-storey blocks with a repeating front façade, featuring a stepped out entrance section leading to the stairway serving wings either side.
Each short wall return (dogleg) protruding corner has been largely rebuilt and further cracking to the junction to both rebuilt and old brickwork was noted.
One of the buildings with two entrances totals some 40 metres in length.
Cause of the Structural Problems
The returns are approximately 450mm. It was recognised that short wall returns (dogleg) on these long façades have performed as one long span with regard to hygrothermal movement, and this has resulted in cracking to the front corner to both old and rebuilt brickwork.
Discussion
From Action Wall Ties’ findings it is apparent, bearing in mind the large area of brickwork façades that have been constructed without the benefit of any expansion joints, that the cracking noted is due to seasonal moisture, thermal expansion and contraction i.e. hygrothermal movement.
Structural Repair Solution
Action Wall Ties’ remedial works are designed to provide a cost effective, long term solution ameliorating all the defects noted, retaining the existing appearance of the brickwork with the minimum of disruption to occupants and impact on the environment.
Action Wall Ties completed a remedial scheme that provided a viable repair by introducing expansion joints, bed joint reinforcement crack stitching.
Action Wall Ties’ experienced skilled operatives installed remedial wall ties either side of the joint before fixing the saw track to the wall and connecting a hydraulic twin diamond bladed saw set to cut a 10mm wide joint to the full depth of the external skin.
Action Wall Ties services are available to clients in the South East i.e. in London, Kent, Sussex and Essex.
Action Wall Ties (AWT) are specialists in masonry reinforcement and repair, providing professional structural repair solutions to a wide variety of structural problems from brickwork cracks to more serious movement. We can retrofit new expansion joints, repair cracks and stabilise walls with a minimum of disruption or fuss. Contact us on 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.
