AWT were the chosen contractors for the Crossrail project at the Victorian Connaught Tunnel in central London. Strengthening, pinning and pressure grouting techniques were used for this vital infrastructure project.
The Crossrail project was to breathe new life into the old Connaught Tunnel. It was built by the Victorians but was, at the time of this work, a disused brick-arched structure lying beneath London’s Royal Docks that survived a hit from a bomb during WW2. This was to be the only existing tunnel to be re-used for Crossrail. Works involved the widening, deepening, as well as strengthening, of the existing structure.
Action Wall Ties’ expertise and experience was sought to undertake the proposed strengthening works to the brickwork arches to the approach cutting, and the damaged area of brickwork rings that form the tunnel. This was to be carried out with the introduction of injected grout, grouted ties and pressure grouting areas where the brick work rings had separated, which was believed to be due to bomb damage.
In line with the Crossrail specification to reconnect the brickwork with the temporary supports in place we firstly drilled vertically 20mm holes 1000mm deep and injected cementitious grout, filling any contiguous voids. Once this was set we revisited the grout filled holes and re-drilled to 25mm for, and injected, cementitious grout and 16mm stainless steel bars simultaneously pinning the brickwork rings together.
After the completion of the pinning, in an attempt to fill any voids to complete the reconnection, we drilled a pattern of 16mm holes with the entrance counter drilled to receive injection packers, ready for the pressure grouting injection. With the pre-batched TamCrete MFC grout mixed and holes flushed with water we injected the grout up to 1 bar over injection pressure, until either hydraulic lock or venting grout from adjacent holes is attained.
Finally, AWT made good the entrance holes with concrete repair mortar.
AWT can provide cost effective structural repairs for a wide range of public sector and infrastructure projects. We operate not only in London but across the whole of the South East of England. We have many years of experience working on large projects, liaising with structural engineers and local authorities.
Contact AWT today to book a survey with one of our experienced team of structural repair specialists. 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.
This low rise apartment block in the North West of London had severe distortion in 2 of the large support lintels. These failing wooden lintels were supporting the stone corbels and brickwork above. There was also deterioration of the brickwork piers including cracked and spalled bricks and cracks in the plinth render.
Failing Timber Lintels in Occupied Apartment Block
The remedial work on entrance hall of this London Soho low rise apartment block was carried out with the residents still in situ. The work was carefully planned to ensure the safety and security of the residents.
Temporary support was provided by specialist props and bracing. This required removal of a section of the stone cornice with a specialist diamond chain saw. The stone cornice and timber beams were then removed.
Installation of New Timber Beams
The remedial work included:
Installation of new timber beams
Realignment of the stone cornice & making good the disturbed brickwork
Spalled bricks were resurfaced
Defective pointing was replaced with colour matched mortar
Damaged render on the plinths was cut away and made good with a specialist concrete repair mortar system.
AWT provided a long lasting and cost effective structural repair with the minimum of inconvenience to the residents. The buildings facade was left ready for decoration to restore it to its former glory.
AWT provide structural repairs for low rise blocks of flats and period properties in London plus the whole of Essex, Kent, Sussex and Surrey.
Contact AWT today to discuss how our structural repair skills could save you time and money in the long term compared to cosmetic repairs by a traditional builder. To book a time for one of our surveyors to visit your property, call us today on 01227 721255, email us at enquiries@actionwallties.co.uk or use our contact form to get in touch.
As can be seen in the photos, there were cracks in both the external brickwork and the internal plaster work around the windows of these school buildings in Harrow, Greater London. In places the external brickwork was crumbling.
The Structural Problem
The brickwork above the windows was visibly lifting and cracking. An inspection by Action Wall Ties quickly identified the cause as corroding mild steel arch bars which were reducing the support from the existing lintel arrangement. This type of fault also results in difficulties with opening and closing windows.
The flat brickwork arches in the building were of differing ages but all were built on mild steel arch bars. As these bars had rusted the resulting ferrous oxide (rust) expanded to several times the thickness of the original metal in turn lifting and cracking the brickwork above. In places the facing brickwork had crumbled to reveal the metalwork.
The Structural Repair Solution
The remedial works were designed to add tensile strength and reinstate the brickwork’s integrity without detracting from the appearance of the building.
The brickwork openings required remedial support and the arch bars needed to be removed to stop any further damage to the building. Bed joint reinforcement and beaming fenestration lintel repair techniques were used to restore the tensile strength of the masonry.
Bricks were carefully removed to allow the cutting and removal of the corroding arch bars. Two rows of twin 8mm stainless steel corded joint reinforcement fixings were installed forming a deep masonry beam. The formation of continuous beams within the existing masonry redistributes the upper storey loads and assists in restraining diagonal cracking and bulging.
Specialist drilling rigs were used to drill for and install helical stainless steel pins through the brick arch and into the line of the deep masonry beam that had been installed within the existing masonry.
Where possible the existing bricks were reused. Replacement bricks were colour matched to blend in with the original brickwork. The cracked mortar was raked out and repaired with new coloured sand and cement mortar to match the existing mortar.
Action Wall Ties serve customers not only in the Harrow area but throughout the South East i.e. Kent, Greater London, Sussex, Surrey and Essex.
Action Wall Ties (AWT) are specialists in masonry reinforcement and repair, providing professional solutions to a wide variety of structural problems including issues with window arches. Contact us on 01227 721 255, use our contact form or email us.
Victorian Terrace with Bulging and Dropping Brickwork
This Victorian terraced home with rendered brickwork in Walthamstow, East London was suffering with dropping and outward bowing of the brickwork.
The Problem
This rendered Victorian terrace home in Walthamstow, London E17, was suffering with significant distortion of the masonry. It also had dropping and outward bowing movement of the brickwork on the upper floor.
The left hand side external brickwork had bulged outward from the centre first floor. Internal movement to the junction of the dividing wall and external wall was also noted.
If structural repairs are sought early enough, AWTs specialist repair techniques may allow for repairs without removing render/pebble dash finishes. However, due to the advanced structural issues with this property, it was necessary to remove the render.
The Solution
The first step, after the initial survey, was to carefully remove the render finish on the front elevation to expose the underlying brickwork. As well as giving access to the brickwork this also allowed for a secondary survey to ensure there were no further issues with the masonry.
Our remedial work included:
Bed Joint Reinforcement Beaming
Crack Stitching
Fenestration Lintel Repair
Lateral Restraints
Grout Tie Injection
Brickwork Repairs
Realignment and Pinning of the Coping Stones
The repair work was designed to reinstate the uniformity of the walls and provide restraint in order to restore the tensile strength of the brickwork. It was also necessary to reconnect the main elevational brickwork to the brick internal dividing and party walls.
Action Wall Ties used specialist drilling rigs that enable precision drilling. State-of-the-art stainless steel fixings were then installed within the framework of the building. These techniques have been designed to deal with the root cause of structural faults rather than just provide a short-term cosmetic fix.
Carefully matched coloured sand and cement mortar was used to make good the drill holes. As can be seen in the photo, there are no visible fixings once repair works are complete. The exposed brickwork is left clean, tidy and ready for repointing. The facade of the house can either be left as exposed brick or the render can be replaced if desired.
AWT’s specialist skills allowed these serious structural faults to be repaired quickly and economically. No long and costly rebuilding work was required.
Action Wall Ties (AWT) are specialists in masonry reinforcement and repair. AWT can advise on structural repairs to properties with render, pebble dash and spar dash. We provide professional solutions to a wide variety of structural problems for home owners in East London as well as the rest of London, Kent, Surrey and Sussex. Contact us on 01227 721 255, email us or use our contact form.
This Victorian/Edwardian terraced home in Lewisham SE4 was suffering with structural defects that were causing cracks in the decorative work around the bay windows as well as bowing brickwork.
The Structural Problem
The beautiful decorative moulding around the bay windows of this terraced home in South East London was cracking. Even more worryingly, the brickwork of the bay window was visibly bulging and rotating away from the main part of the house. Inside the house there were cracks appearing in the internal party wall.
Action Wall Ties were called in to find a permanent solution to the structural issues while preserving the period features of the property.
The Structural Repair Solution
The AWT’s survey team diagnosed inadequate restraint of the bay window and a point loading issue with the party wall. Reinforcement of the masonry and a redistribution of the load on the party wall was required.
AWT have an arsenal of techniques at their disposal that are not available to traditional builders. This allows them to repair structural defects without rebuilding works.
Following a thorough survey, the following techniques were selected to restore the structural integrity:
Bed Joint Reinforcement Beaming
Crack Stitching
Grout Tie Injection
Lateral Restraints
Concrete and Brickwork Repairs
The specialist tools and equipment developed by AWT allows them to repair structural defects without compromising the look of a period property such as this.
A twin diamond bladed machine with attached vacuum was used for precision drilling prior to the installation of rows of twin 8mm stainless steel corded joint reinforcements. This helped to redistribute the weight of the upper storey to those parts of the supporting structure best able to carry them. It also assisted in restraining diagonal cracking and bulging.
8mm stainless steel lateral restraints screwed into the floor joists’ bresummer beam and resin bonded to the masonry provided further lateral restraint.
Localised cracks in the brickwork were stitched together using stainless steel fixings embedded out of sight within the brickwork.
Any patches of defective masonry were cut away and the areas were repaired using Flexcrete – a specialist repair substrate.
The finishing touches included colour matching any replacement bricks and ensuring the pointing style and mortar mixture matched the existing texture and colour.
AWT’s specialist skills allowed these serious structural faults to be repaired quickly and economically without damaging the character of the period features.
Action Wall Ties (AWT) are specialists in masonry reinforcement and repair. We provide professional solutions to a wide variety of structural problems for home owners in Lewisham and the whole of London, Kent, Surrey and Sussex. Contact us on 01227 721 255, email us or use our contact form.
This Victorian/Edwardian terraced property with a render finish in South East London was suffering from advanced brown rot in the wooden bay window lintel and floor joists.
The Structural Problem
Brown Rot had taken hold in the horizontal load bearing timber beam in the front bay window of this home in the Hither Green, SE13 area of London. The rot had also spread to the adjacent cantilevered floor joists.
The beam and joists were no longer strong enough to support the weight of the building. The bay window area of the property was becoming unstable. The brickwork was cracking and bulging.
If structural repairs are sought early enough or if the structural defect is localised, as in this case, AWTs specialist repair techniques may allow for repairs without removing the render. The small disturbed areas of render can then be made good with a concrete repair mortar system.
The Structural Repair Solution
Action Wall Ties acted quickly to firstly stabilise the structure to prevent further movement.
Before installing temporary supports and starting to uncover the Bressummer beam AWT installed Bed Joint Reinforcement Beaming both externally and internally. Box beams were also installed.
Bed Joint Reinforcement Beaming requires precision drilling and injection of stainless steel bars and Cementitious grout into the brickwork. No fixings are visible once the work is complete. Re-pointing with colour matched sand and cement mortar gives a neat finish.
This vital work redistributed the upper storey loads to those parts of the supporting structure which were best able to carry them. It also assisted in restraining any further diagonal cracking and bulging of the brickwork.
When the temporary supports were in place the bay window beam and rotten floor joist were replaced. With the structural integrity restored, this property can now continue to be a home for many years to come.
AWT can provide cost-effective structural repairs for a wide range of structural faults including rotting wooden beams. AWT can advise on structural repairs to properties with render, pebble dash and spar dash finishes. We operate not only in SE London but across the whole of London and the South East of England.
This traditionally built mixed retail and domestic mid-terraced property in Greenwich, SE10, had visible bulging of the side wall.
The Structural Problem
The side wall brickwork of this property in was visibly bulging outwards. Movement was also noted within the property with some visible cracks.
The property located in South East London had retail space on the ground floor with domestic residences on the upper floors. Access to the flank wall was hindered by an abutting pitched slate roof which made access difficult.
Action Wall Ties needed to devise a structural repair scheme that would provide a lasting repair with minimal impact on the retail space, the residential space and the neighbouring properties.
An alternative to long, disruptive and costly rebuilding work was required.
The Structural Repair Solution
AWT needed to ameliorate the masonry defects and add tensile strength to reinstating the brickwork’s integrity. A three pronged strategy was used:
Bed Joint Reinforcement Beaming
Lateral restraints
Brickwork repairs and infill
AWT used carefully designed scaffolding to access the defective masonry while taking care to protect the slate roof of the neighbouring property.
The wall contained an arched window opening that has been boarded over internally. The old sash window was removed and the opening was bricked up with colour matched bricks. Any damaged bricks were replaced.
Internally the installation of timber noggins and lateral restraints provided restraint of the lateral movement of the masonry. The stainless steel lateral restraints were screwed directly into the timber studs and then resin bonded to the masonry to provide a permanent solution to the lateral movement.
AWT used their precision diamond drilling equipment to install rows of twin cord reinforcement, forming a deep masonry beam. This redistributes the weight of the upper storeys. It also acts as a restraint to diagonal cracking and bulging.
Repointing the disturbed mortar with colour matched mortar provided the finishing touch.
AWT provide cost effective masonry repairs to customers throughout London and the South East.
