Cavity wall ties
Cavity Wall Tie Failure
Cavity walls incorporating metal wall ties have been used since the beginning of the 19th century, and have become the standard form of construction for housing and buildings. A cavity wall comprises of an outer leaf and inner leaf of brickwork or block-work, with a cavity in between. The two leaves are tied together with galvanised steel wall ties.
Over recent years, it has become apparent that a high number of properties built before 1981, are suffering from premature wall tie corrosion. The latest research has found that the wall ties corrode faster in the external leaf of brickwork, leading to lamination where they will expand to several times their original size. This expansion will cause structural instability, by lifting the mortar joints where they lay.
Research has also found that a high percentage of properties inspected, had an inadequate number of wall ties, especially around openings, i.e. windows and doors.
Symptoms of wall tie failure
• Visual evidence of corrosion can be seen by horizontal and diagonal stepped cracking to rendered external wall surfaces, or the bed joints of the brickwork.
• If corrosion is severe, it can lead to distortion and bulging of the wall. In some extreme cases, external walls have collapsed during gales.
The first step to remedy the situation is for a comprehensive survey to be carried out in order to identify the cause of the problem.
1. A visual inspection will be made in order to identify any cracking or bulging in the brickwork.
2. The locations of any existing wall ties are identified by using a metal detector.
3. An endoscope is used to examine the condition of wall ties within the cavity.
4. Sometimes a brick may have to be carefully removed in order to aid an inspection.
Installation of Remedial Wall Ties
If corrosion of existing wall ties is identified, the corroded wall ties can be either removed or isolated in accordance with recommendation laid down by B.R.E. Digest 329. Replacement stainless steel wall ties can then be installed at staggered intervals conforming to BS 5628 code of practice, fixed either mechanically or with resin.
Lack of Cavity Wall Ties
If during our survey it transpires that insufficient wall ties have been incorporated during the construction of the building thereby causing cracking or bulging to the brickwork, additional wall ties can be installed, again in accordance with the current building code of practice. Where applicable, recommendations can be made with regard to any repair work deemed necessary to the structure.
As an approved contractor for Permagard Products Ltd, a 10 year guarantee can be offered, subsequent to the completion of the contract and receipt of payment.