Wall Ties

Wall tie corrosion affects many properties in the UK especially in coastal and exposed locations. The mild steel or galvanised wire ties embedded in the mortar eventually start to corrode and in its advanced stages the corrosion will cause horizontal cracking and eventually loss of stability between the two skins of brickwork.

« A corroded iron twist wall tie. This photograph is taken using the Allen Inspector Scope attached to a Sony Mavica camera. Ideal for inclusion within Structural Engineers reports.

The design of cavity walls invariably incorporates the use of metal wall ties. Such a system has been in use since the beginning of the nineteenth century to prevent rain penetration and to improve thermal insulation. Cavity Wall-ties provide an integral support in walls constructed with a cavity between the inner, load bearing, skin of masonry and the outer, weather shield, skin. The outer skin is normally very thin in relation to its height and without support would be subject to damage by extreme weather conditions.

Research by the BRE (Building Research Establishment) has found that wall ties corrode faster within the mortar joints of the external leaf of brickwork where rust, which causes expansion of the tie, builds up around the 'fish tail' ends of the ties. This expansion will cause blistering of the mortar joints (at tie courses) creating consequential structural instability. Over recent years it has become apparent that a high number of properties, built prior to the early 1980s, are suffering from cavity wall tie failure due to corrosion of the metal. This is principally due to poor quality galvanising standards prior to that time.. Visual evidence of corrosion can be seen by horizontal cracking to the mortar joints of external wall surfaces or hairline cracking to external render. If corrosion is severe or neglected for an extended period this may lead to bulging of the wall.

DWC/Regent Homeguard surveyors have also found evidence of a lack of the correct density of wall ties particularly around reveals. It is also worth mentioning that properties do not need to be in excess of 100 years old to require remedial wall tie work! Over the past few years DWC/Regent Homeguard surveyors have found the need to install supplementary wall tie systems when insufficient ties have been found in relatively 'new build' properties ( only discovered when the property owner changed the window casings!). The location of a property will have a significant bearing on the extent of corrosion. This will inevitably vary around the country. For example, on the south coast of Kent and Sussex exposed southern facing elevations deteriorate more rapidly than the remainder of the property therefore requiring only partial replacement of the wall tie system to the southern elevation. The opposite may be the case in the North West and North East of the country.

WALL TIE REPLACEMENT SPECIFICATION

The following specification is the usual specification for a full wall tie replacement system of course subject to survey.

Erection and dismantling of any ladder access necessary to complete works safely. Any requirement for additional access, such as scaffolding or towers, will be at additional cost.

Location of the existing cavity wall tie irons using a specialist metal detector.

Installation of stainless steel wall ties spaced and positioned in accordance with current BRE329/401 recommendations.

Random 'pull out' testing of several new ties using a hydraulic tension tester in order to ensure that a correct fixing has been achieved and that the most suitable model of tie is being used.

Where necessary the structural isolation of remaining ties over affected areas in order to ensure no further damage can occur as a result of corrosion. The method of immobilizing the original ties is dependent on the condition of any samples which are first removed and inspected.

Structural isolation of the original wall tie system is not always necessary. Where wire/butterfly ties have been used, isolation would not normally be required.

Occasionally full removal of the original system is necessary, particularly where internal cracking has resulted from corrosion. This is rare and will usually be the result of a Structural Engineers recommendation.

The making good of any brickwork, render or mortar disturbed during the installation process. This does NOT allow for specialist types of render finish, pebbledash or plastic coatings. External redecoration will NOT have been allowed for. We will NOT accept responsibility for disturbing pre existing faulty or blown render.

Removal of any debris created by the works, leaving the adjacent site or garden in a clean and tidy condition.

DWC Regent Homeguard Contractors & Surveyors only use remedial ties from corrosion resistant '18/18' stainless steel. Our technicians use sensitive hydraulic 'pull out' equipment to test every job done thus ensuring complete quality control. No one make or model of wall tie is right for all buildings. We are not connected or 'tied' to any manufacturer of wall ties and will install the tie most suitable for the property. Random testing is carried out using the Hilti 'Pull Test' kit to 1.5kn or to a strength specified by a structural engineer.

IMMOBILISATION (ISOLATION):

Apart from the installation of new stainless steel wall ties, the most important aspect in wall tie replacement is the correct immobilization of the original cavity wall ties.

When cavity wall ties corrode they expand. This expansion causes characteristic horizontal cracking which appears in external walls at 'tie courses'. This expansion can eventually lead to serious damage occurring, which may require extensive rebuilding. In view of this it is essential that the original ties are properly immobilized by structural isolation as mentioned above.

Wall tie replacement is a structural repair. We employ our own trained installation technicians and do not employ 'labour only' contractors to carry out wall tie work. During the course of repairs the interests of property owners are protected by the DWCs public liability insurers.

GUARANTEE:

DWC Regent Homeguard Contractors & Surveyors are registered installers and a member of the Wall Tie Installers Federation (WTIF) and are approved to issue WTIF Insured Warranties on completed works. The Warranty is valid for 25 years and is transferable to any new owner of the property. For avoidance of doubt the obligation to indemnify extends to all damages, costs, expenses and liabilities arising as a result of any financial loss incurred by our customers pursuant to the wall ties and workmanship failing to perform their intended function.

Some banks and building societies prefer to have this sort of structural repair work supervised and the completed workmanship certified by Consulting Engineers or Chartered Building Surveyors. We can arrange for works to be independently supervised and the completed workmanship certified, however independent supervision would involve additional costs in accordance with the engineer's published fees.

 

Wall Tie Videos

 

 

 

 

 

Structural Reinforcing

Lintel repair, wall tie replacement systems, crack repairs and masonry pinning

DWC together with its Axis Stabilisation division will attend to properties which are affected by all manner of structural problems - from specialised underpinning techniques involving the installation of Shire Piles to remedying structural defects in historic buildings and installing flexible helical reinforcement bars in existing mortar beds to remedy cracked brickwork and defective lintels. We show below a sample of the works which have been undertaken by DWC/Regent Homeguard & Axis Stabilisation:

Bespoke Solutions from Axis Stabilisation

Expertise in structural engineering services is vital for a successful project. Axis has been honing its skills since 1989 in the repair and stabilisation of all types of structures and ground problems. Often the problem is unique to the project and a one-off design and system has to be comissioned. Working with architects and engineers, Axis has been at the forefront of the industry.

Axis Stabilisation draws on a wealth of knowledge from within our organisation. However, as complex designs and remedies dictate, we are able to utilise the services of our development facilities. From the moment we receive your enquiry it will receive our fullest attention until satisfactory completion and beyond. Our office staff, surveyors and management team will dedicate themselves to ensuring that the design, costs, programming and supervision are the most appropriate.

Services include: Crack Stitching, Subsidence & Structural Reinforcement including custom structural solutions.

 

You are invited to visit www.axisanchors.co.uk for further details

 

CASE STUDY

LINTEL REINFORCING BARS AND CRACK STITCHING IN BRIGHTON

Milner flats, Brighton were undergoing re-pointing works, when it was found that there had been structural movement to several sporadic areas of the building, which required reinforcing. DWC/Regent Homeguard Contractors & Surveyors were instructed to install a series of lintel reinforcing bars and to stitch cracks in the outer leaf of the brickwork.

 

MORTAR BED REINFORCING USING THOR HELICAL STEEL BARS & EPOXY GROUT - EASTBOURNE COLLEGE

The photograph is of an Annex to the main college, which is of flint construction. Several cracks had opened up around the external flint panels and these required tying back to the main structure. In addition, several mortar joints also required mortar bed reinforcing using Thor Helical steel bar and epoxy grout.