WALL TIE REPLACEMENT STRATEGY
Where any type of cavity tie failure has been established the walls should be immediately stabilised using a proprietary replacement wall tie system. 
Where each masonry leaf is at least 90mm thick the remedial wall ties are installed into the wall at a density of 2.5 per sq. metre.  Ties should be spaced at centres measuring no more than 900mm horizontally and 450mm vertically, in a staggered ‘domino 5’ pattern.  Additional cavity ties should be installed adjacent to open reveals at vertical centres not exceeding 300mm (or 1 tie per 300mm in height in the case of a gable apex.

Wall tie replacement systems are simple to install and can be carried out by most general builders and competent DIY enthusiasts.  Care should be taken to use light weight drilling machines when drilling through the walls to minimise damage to the cavity face of the near most leaf as the drill bit breaks through.  Percussion drills are accordingly the drilling machine of choice and the heavier varieties of SDS drills are best avoided..
Where wall tie corrosion and volumetric expansion has resulted in horizontal cracks to the brickwork, the potential for continued expansive damage should be assessed and weighed against the damage that could result from efforts to cut out, remove or isolate all the corroding metals buried in the wall.  This is a job for a qualified engineer, who will establish whether maximum expansion has already occurred or whether the ties have potential to expand further and to worsen the cracks.