CAVITY WALL TIE
incorporating metal ties have been in use since the beginning of the nineteenth century
.These ties hold the outer leaf of the wall to the inner leaf. The early metal ties
produced mainly from wrought or cast iron performed satisfactorily but in more recent
years mild steel ties have been used and despite galvanising or bitumastic treatments have
been found to suffer from corrosion.
A number of
cases of distress of cavity walls, attributable to wall tie failure, have occurred in the
United Kingdom and it is now clear that the problem could eventually affect all the cavity
walled structures built before 1981, some 10 million dwellings, and will not in future be
confined only to cases of poorly made ties.
failures reported to the Building Research Establishment (BRE) include inferior coatings
of bitumen, insufficient zinc galvanising on mild steel, aggressive mortars (particularly
black ash), exposure to marine climates and permeable mortars such as lime that permits
Once the steel
of the wall tie is exposed to air and oxygen the all too familiar rusting cycle begins.
The rate of corrosion will be governed by site conditions but in severely exposed
locations the life of the twist tie could be reduced to ten years. It was estimated in the
1986 Survey of English Houses that around 12 million properties exist with cavity walls of
which the number requiring some repairs to wall structures is approaching one million.
It must be
stressed that wall tie failure, or cracking of the outer leaf of a domestic property is
rarely an immediate threat to the safety of the occupants. The risk is greater to
pedestrians and adjacent property and measures must be taken to restrict access to the
risk areas if severe wall tie failure is diagnosed.
installation of wall ties in an existing property may be needed to:
Stabilise a cavity wall damaged by corrosion of vertical steel twist ties.
Stabilise a cavity wall rendered unsafe by the loss of wire ties by corrosion.
Increase the number of walls ties in a cavity wall constructed with insufficient
Tie back existing cladding walls to concrete, steel or timber frame structures.
Stabilise two parallel single-leaf walls with space between not exceeding 25mm tied
together with solid mortar, where the two leaves are separating.
Tie new walls or bulging walls back to existing cross walls.
Tie walls either side of cuts made for insertion of openings or movement joints.
of properties (basements, vaulted cellars, coal stores) can be converted into part of the
living accommodation or additional offices/store rooms if part of a commercial property.
carried out a survey we would supply a detailed report and specification for the method of
tanking/dry lining that is appropriate.
running water is visible to wall surfaces or standing water is present on floor surfaces a
suitable tanking/dry lining system can be recommended.