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.
Imposing 1980s quadrangle designed head office building in Essex with failing brick slips. The contract for remedial fixing of the brick slips was awarded to Action Wall Ties.
The subject building was an imposing 1980s quadrangle design commercial head office building, over four floors, in four wings with entrance towers to each corner.
This building was undergoing a major refurbishment for new occupants Cofunds when some detached brick slips were noted. Action Wall Ties was invited by Como Interiors to undertake an inspection of the brick slips and any associated defects, and to report our findings and recommendations.
Action Wall Ties inspected Mayland house building, identified the defect, reported on our findings and recommended AWT designed fixing of some 20,000 brick slips.
Action Wall Ties was instructed and successfully completed the fixing of 20,000 brick slips to this building on budget and on program. Our work met with the approval of both Como and Cofunds.
The Structural Problem
The building was found to be of concrete frame construction, with cavity brickwork infill walls, an external skin of stretcher bond reddish multi-stock bricks constructed on each concrete floor beam with brick slip facing, and with windows up to the underside of the floor beam above in-between brick clad columns.
The external brickwork infill walls were found to be supported on the floor beam by approximately 60mm, with 50mm protruding to accommodate finishing and with brick slips bedded in front of the concrete floor beam, thus giving the appearance of brickwork. To each wing the brick slips formed a full brick soldier course with three courses of stretcher bond to the return wall and the entrance towers.
Since this building was built the concrete frame had shortened, and the bricks’ first irreversible expansion had taken place. We believed that these movements, together with thermal movement, had resulted in the sand and cement bedding mortar becoming detached from the concrete floor beam. Any further movement within the brickwork, and/or erosion/deterioration of the pointing mortar, could un-lock the brick slips allowing them to become dislodged and fall. Present-day practice is to mechanically fix all brick slips.
The Structural Repair Solution
Action Wall Ties have considerable experience in remediating brick slip defects and have developed methods and equipment to enable the successful fixing of brick slips in situ, avoiding damaging (i.e. cracking with impact hammer type drills) the delicate brick slips. With specially sharpened drills, developed to enable rotary drilling of the slips to complete the fixing, we inserted a special colour matched epoxy putty into the pre-drilled hole then drove a stainless steel fixing into the epoxy putty to fill hole, providing not only a mechanical fixing but bonding all the elements together. We then made good and sealed the access hole with coloured epoxy putty.
Action Wall Ties have developed a unique approach to fixing brick slip issues on low rise and high rise concrete frame buildings. Using their specialist drilling techniques and carefully designed fixings, AWT can repair brick slip defects in an economical manner that maintains the appearance of the building and minimises disruption.
Kent based AWT provide their expertise to customers in Kent, Essex, Sussex, Surrey & London. To arrange a survey or to discuss your project, please call us on 01227 721 255, email us or fill in the contact form.
Seven-Storey Building NHBC Warranty Remedial Works
This seven-storey building in Croydon, South London required remedial work under the NHBC warranty scheme. This included stainless steel support angles, horizontal soft joints and Sika CarboDur strengthening carbon fibre plates.
The subject building was a contemporary designed seven-storey apartment building.
The Structural Problem
The building was found to be deficient from the one that had been designed and remedial works were instigated by NHBC warranty. Consulting structural engineers were engaged to design the required compliant remediation works and Action Wall Ties were engaged to undertake the works.
The Structural Repair Solution
The remedial works involved the introduction of stainless steel support angles with horizontal soft joints and Sika CarboDur strengthening carbon fibre plates to concrete beam, together with remedial wall ties and bed joint reinforcement.
We removed the external brickwork skin exposing the concrete beam and prepared the concrete surface removing any ridges with a concrete planer, cleaned and primed ready for and applied Sika CarboDur structural strengthening system 80mm strips bonded with Sikadur 30 in accordance with manufactures and AWT methods. Thereafter, we installed stainless steel support angles and reinstated the brickwork.
AWT are structural repair contractors. We work with local authorities, housing associations, the NHBC and other organisations to provide cost effective structural repairs to both low rise and high rise blocks. Our repair techniques ensure the minimum amount of disruption to residents.
AWT are available for contracts in Kent, Sussex, Essex, Surrey and the whole of London. Please get in touch using our contact form, by calling 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.
