Structural Solutions / Wall Tie Replacement:
Wall ties are an important structural component ensuring the stability of the outer leaf of a cavity wall against wind loads. The condition and number of wall ties in the structure are important and where corrosion has set in or wall ties are missing or broken, then remedial ties will be required. Solid masonry may also delaminate through broken headers or deteriorated mortar and require remedial tying to ensure future stability.
Corroded Wall Tie in the cavity:
This Picture shows typical wall tie damage where the corroding and delaminating tie in the joint is expanding and causing the mortar joint to crack and de-bond leaving a regular pattern of cracking every six courses on most buildings.
The Maclennan Answer to the Problem
Helical remedial ties are stainless steel, corrosion resistant and flexible to accommodate natural building movement. They are easy to install and test in the building under repair, leaving nothing to chance. Where drilling through the brick face is not acceptable then it will be necessary to consider inserting the remedial ties through the mortar bed. This will be satisfactory where the mortar is strong and in good condition. Angled drilling may also be used in special circumstances.
Testing and Spacing:
Pre-specification testing should be included as a routine part of the building survey. At least one, and preferably two, ties should be inserted into each elevation at different levels to determine the minimum pull out load obtainable from both near and far leaves. This minimum load should be used as the basis for deciding the density of ties to be installed. This testing is carried out by all Maclennan Surveyor’s when contracts are awarded or for a small cost at tender stage. For a small contract at least 10 ties must be tested; on large projects 5% of all ties should be tested. For most applications (buildings under 30m high and areas with a maximum wind speed of less than 46m/sec) the minimum tensile proof load is 1kN based on a tie density of 2.5 per m (900mm x 450mm centres). This excludes cladding form masonry and substrates below 100mm deep.
Independent Testing and Approvals:
Helical remedial products have been independently and vigorously tested in a wide range of common materials. The testing programme is on-going and to date has been carried out by the Civil Engineering Department of Oxford Brookes University; the Civil & Structural Engineering Department of Middlesex University; The Transport Research Laboratory, Crowthorne and the Building Research Establishment, Garston.