Wall Ties – General Information
Cavity wall construction has almost entirely replaced solid wall construction in the United Kindgon. Evolving in the latter part of the nineteenth century, and becoming common in dwellings in northern and western Britain in the early 1900s. It became much more widespread during the building boom of the 1920s, and from 1945 onwards, cavity wall construction has become virtually standard throughout the house building industry.
In the very early days, ties were either left unprotected or were given a bitumen coating. During the early 1930s, zinc coated ties or galvanising became more accepted. Houses built before 1945 have an unknown tie life expectancy. Those built between 1945 and 1964 have an expected zinc life of between 30-60 years for strip ties (fishtail) and 15-30 years for wire ties (butterfly). The expected life of ties between 1964 and 1981 is estimated at 23-46 years for strip ties and 13-26 years for wire ties.
Statistics from the 1986 survey of English houses published by HMSO indicated that a total of 11.3 million houses were built between 1919 and 1986, and of these 906,000 required repairs to the wall structure, resulting from corroding wall ties.
ALL mild steel wall ties will eventually corrode, the only question is, when?
Common Causes of Wall Tie Corrosion
Porosity of brickwork
Brick vary considerably in their moisture absorption rate. Engineering bricks are almost impervious to moisture and water. Softer bricks, however, behave like sponges.
Quality of mortar
Weak lime mortars are more porous than dense sand and cement mixes.
The chemical action of mortars can vary between two extremes, either pacifying or encouraging corrosion. Ordinary Portland cement mortars are alkaline in nature and as such disclosure the corrosion of embedded ferrous metal. Other mortars will contain a proportion of sulphates which, when combined, with moisture, created a more aggressive condition than normal.
The location of any given elevation will determine the life expectancy of the wall tie, e.g. coastal industrial or locations of persistent driving rain, are all vulnerable. The presence of salt within the atmosphere and coastal locations result in accelerated corrosion wall ties. Industrial conditions will increase the acidity of the moisture reaching the ties, this can lead to a more aggressive and corrosive condition. Driving rain, by its very nature, increases the period at which the wall and its ties may be persistently wet. South and west facing elevations are more vulnerable than those on the north and east of the building. Poor design and construction problems including the lack of an effective damp proof course, blocked cavities, inadequate flashings and lack of cavity trays, are recognised contributing factors to the ingress of moisture.
Symptoms Common to Tie Failure
As wall ties corrode, bed joints widen and the outer leaf grows upwards causing tension in the inner leaf, therefore bending movement in the wall as a whole. Outward movement or bulging of the wall usually results with the inner leaf of the wall often being carried outwards as well as the ties which are normally intact to some degree at this stage.
Other common symptoms include vertical and horizontal cracking, sagging of lintels, upward cambering of window sills, lifting of roof edges, separation of window reveals, and separation of floors.
Whilst these symptoms are common and can be related to wall tie failure, the can also be characteristic of more serious structural defects. If damage exists which is not consistent with wall tie corrosion, a structural engineer should be employed to investigate further. An inspection carried out by Anchor Property Care does not constitute a structural inspection.
An assessment of existing cavity wall ties within the construction may include the use of various types of specialist equipment, including boroscopes, wall tie locaters, and metal detectors.
As ties are located, the condition of the wall ties are assessed and any recommendations and/or a specification for remedial action works is submitted, dependent on the severity of the problem and the specific type of wall tie.
Anchor Property Care have an extensive range of high quality stainless steel remedial wall ties to suit all applications and completed to our high cosmetic standard.