Low rise blocks 1930s - 1950s Archives

Fixing Cracking Above Concrete Boot Lintels

Concrete boot lintels to window openings were in common use in the 1970s and have the unique appearance of a visible one course high concrete toe that appears not to have any bearing onto the adjacent brickwork (i.e. the visible concrete toe is in between the brickwork reveals).

Many low rise blocks from the 60s and 70s develop defects that require concrete boot lintel repairs due to cracks, gaps and sagging brickwork above the windows. Failure to address these issues promptly can lead to dangerous, collapsing masonry as well as extensive damage to internal walls.

AWT are able to provide long term, cost-effective boot lintel repairs with minimal disruption to residents.

Concrete Boot Lintel Problems

Boot lintel gaps cracks rotation - Fixing Cracking Above Concrete Boot Lintels

Boot Lintel stepped cracks - Fixing Cracking Above Concrete Boot Lintels

Boot Lintel gaps - Fixing Cracking Above Concrete Boot Lintels

Boot Lintel compression - Fixing Cracking Above Concrete Boot Lintels

Rotating Boot Lintel Causing Gaps & Cracks

Stepped Cracks Due To Failing Boot Lintel

Gaps Above Concrete Boot Lintel

Boot Lintel Defect Causing Compression Cracks

As shown in the gallery, in the 60s and 70s, many concrete boot lintels were incorrectly fitted onto unsuitable bearing allowing the lintel to rotate and the supported brickwork to drop and crack.

This fundamental flaw in the installation of concrete boot lintels means that the weight of the heavier brick outer skin is too great for the relatively soft and lightweight inner blocks to support. The lintel rotates, causing gaps to open up, compressing the blocks of the inner wall and causing the outer brickwork to sag.

Common symptoms of boot lintel problems:

Cracks in the visible part of the concrete lintel
Stepped cracks in the brickwork above windows/doors
Dropping of the brickwork above windows/doors
Bulging or bowing brickwork above windows/doors
Cracks in the internal walls and ceilings above windows/doors
Warped window/door frames making them difficult to open and close

Chris Nichols explains, “This type of lintel has no bearing onto the external brickwork the concrete lintel rarely fails. (As with any concrete the toe of a boot lintel can be affected by corroding reinforcing bars and require concrete repairs.) The boot lintel is reliant on the bearing onto the internal skin. The internal skin bearing the lintel should be of a material capable of withstanding and spreading the load (e.g. pad stone concrete blocks or engineering bricks). “

“In many cases the lintel was bedded directly onto lightweight blocks that are unable to take the imposed load and compress the outer edge of the bearing, rotating the lintel and allowing the external brickwork above to crack and drop as described in BRE Good Building Guide 1.”

case 55 a - Fixing Cracking Above Concrete Boot Lintels

case 55 d - Fixing Cracking Above Concrete Boot Lintels

case 55 b - Fixing Cracking Above Concrete Boot Lintels

case 55 c - Fixing Cracking Above Concrete Boot Lintels

case 55 e - Fixing Cracking Above Concrete Boot Lintels

Cracking Concrete Boot Lintels

Gaps & Cracks Above Concrete Boot Lintel

Gaps & Cracks Around Concrete Window Lintels

Rotated Boot Lintel Causing Gaps

Boot Lintel Problems Due To Incorrect Installation

Concrete Boot Lintel Repairs

Action Wall Ties provide a cost-effective, long term solution that retains the existing appearance of the brickwork with the minimum disruption to the occupants and the environment.

Action Wall Ties have developed a remedial system and methods, including specifically designed equipment, to remedy the problem of cracked concrete boot lintels. Action Wall Ties slightly anti-rotate the lintels back in place, drilling for and then resin bonding 16mm stainless steel shear pins to both end bearings. Once the resin bonded fixings are set the props are released, pre-loading the shear pins, thus reducing any further cracking.

To larger openings and with advanced movement it may be necessary to introduce two rows of twin cord reinforcement, forming a composite deep masonry beam. To the underside of the concrete toe, we drill for and inject grouted 8mm helical stainless steel pins passing into the line of the deep masonry beam to arrest any further rotation of the concrete lintel.

Action Wall Ties concrete boot lintel repair and replacement solutions are available to clients in London and the South East.

Action Wall Ties (AWT) are specialists in masonry reinforcement and repair, lintel repairs, replacing a damaged lintels, and providing professional solutions to a wide variety of structural problems. We work with home owners, London boroughs, social housing providers, architects, project managers, local authorities and insurance companies.

Contact us on 01227 721 255, or email us.

1930s style low-rise apartment blocks

1930s style low-rise apartment blocks in London

An estate of 1930s style low-rise blocks of apartments with defective balustrade walls (half-brick thick) to access deck and private balconies – AWT’s remedial scheme – remedial restraint posts, removal of the existing reinforcing rebars.

The subject buildings are 1930s style low-rise blocks of apartments, conventionally built of solid brickwork and concrete floors, with open access decks and private balconies.

Structural Problems

• Visible cracking and previous repairs (in a similar pattern) were noted to the balustrade half-brick thick walls.

• Generally the brickwork and pointing was found to be in good condition, with little spalled pointing and bricks noted. Previous repairs to the access decks and private balconies balustrade half-brick thick walls in a similar pattern were noted.

• All access decks and a representative sample of private balcony balustrade walls were inspected and scanned, locating the reinforcing bar position. Some bars were uncovered, inspected and photographed. In the main, previous repairs correspond to the pattern of the existing reinforcing bars.

• The reinforcing bars uncovered were the old ½ inch rebar bent up from the concrete slab and built into the centre of the brickwork up to, and possibly into, the cast in-situ concrete coping.

Discussion

The existing half brick balustrade walls contained mild steel reinforcing bars. From our investigations it was apparent the damage to the brickwork (cracking/spalling/previous repairs) resulted from the expansive corrosion of these bars which reduced the effectiveness of the bar, especially at the asphalt tuck line leaving the wall vulnerable to failure represent a safety issue.

The reinforcing bars viewed had corroded, delaminated and expanded, rendering the bars ineffective. The half-brick thick balustrade wall’s stability is dependent on the reinforcing.

Wrought iron decorative panels, built in lugs viewed, assessed to be corroded, delaminated and expanded, lifting and cracking the brickwork.

Stuctural Repair Solution

AWT have previously successfully completed remedial schemes to ameliorate similar defects at many other blocks.

AWT’s remedial scheme involved the development of methods and the design of equipment to enable us to undertake the remedial reinforcement, installing restraint posts, expansion joints, removal of the existing reinforcing rebars and thereafter make good the brickwork to the balustrade walls, to the access decks and to the private balconies.

The remedial scheme also alleviated the need for the removal and replacement of the balustrade walls, along with all the associated problems that this would have entailed for the occupants with the added benefits of a considerable cost saving and resulting impact on the environment.

Action Wall Ties (AWT) are specialists in masonry reinforcement and repair, providing professional solutions to a wide variety of structural problems in Kent, London and Surrey. Contact us on 01227 721 255, or email us.

1950s style four-storey block of flats

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.

1930s style low-rise apartments with balustrade wall defect repairs

An estate of 1930s style low-rise blocks of apartments with balustrade wall defects – corroding mild steel balusters cracking masonry to half-brick thick balustrade walls – removal of the baluster embedded into the coping stone and brickwork,

The subject buildings are 1930s low-rise blocks of apartments in London, of conventional brick and filler joists construction, with open access decks and private balconies.

The Structural Problem

Cracking and dislodging of the brickwork and coping stones to the balustrade walls of the private balconies was reported and noted.

Discussion

Action Wall Ties investigated the defects and reported that the causation was found to be due to expanding corrosion of the handrails mild steel supporting balusters built into the masonry.

The corrosion of the embedded mild steel results in the formation of ferrous oxide that expands to several times the thickness of the metal it has resulted from, thus breaking out of the brickwork splitting bed joints and lifting of the brickwork.

Structural repair solution

Action Wall Ties remediation involved cutting the baluster at the coping stone line, removal of the baluster embedded into the copping stone and brickwork, and completing repairs to the brickwork and coping stone. AWT re-drilled holes down into the walls for grout and designed all the necessary stainless steel fixing plates, thereafter welding the original baluster to a fixing plate.

Action Wall Ties (AWT) are specialists in masonry reinforcement and repair, providing professional solutions to a wide variety of structural problems in Kent, London, Surrey and Essex. Contact us on 01227 721 255, or email us.

Balustrade wall defects

Balutrade wall defects in West London

An estate of 1930s style low-rise blocks of apartments in West London with balustrade wall defects – remedial restraint posts to walkway balustrade walls, cutting expansion joints

The subject building is part of an estate of 1930s style low-rise blocks of apartments in West London of conventional brick and filler joists built construction with open access decks and private balconies.

Problems with cracks in the Balustrade walls

This very large building is curved with convex walkway balustrade walls.

Outward stepping at the base of the walls, together with outward leaning and cracking of the brickwork and coping stones to the walkways’ balustrade walls, was reported and noted.

Discussion

Action Wall Ties investigated the defects and reported that the causation was found to be due to seasonal moisture, thermal expansion and contraction i.e. hygrothermal movement.

The expansion had pushed the walls outwards, in some cases stepping out the base of the wall and the wall leaned outwards.

Structural repair solution

Action Wall Ties remediation works are designed to provide a cost effective long term repair solution, ameliorating the defects noted, that retains the existing appearance with the minimum effect to the occupants and impact on the environment.

To stabilise the balustrade wall Action Wall Ties completed remediation, involving cutting expansion (movement) joints and the design fabrication and fixing of restraint posts.

Action Wall Ties (AWT) are specialists in masonry reinforcement and repair to balustrade wall cracking and problems, by providing professional solutions to a wide variety of structural problems in the Kent and London areas. Contact us on 01227 721 255, or email us.

Cavity Wall Construction History

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

case 54 d - Cavity Wall Construction History

case 54 c - Cavity Wall Construction History

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.

rusty wall tie repairs kent - Cavity Wall Construction History

wall tie 1 - Cavity Wall Construction History

wall tie 2 - Cavity Wall Construction History

wall tie - Cavity Wall Construction History

rusted wall tie - Cavity Wall Construction History

rusted wall tie1 - Cavity Wall Construction History

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.

Contact us to discuss your requirements or book a survey on 01227 721 255, or email us.

Replacement of Failing Timber Lintels

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.