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The need for remedial wall ties was established in the early 1980’s, when wall tie failure was discovered as being a widespread problem across the UK. Before then wall ties were generally manufactured from mild steel and commonly protected by a sacrificial zinc coating. Tie irons were expected to last the lifetime of a building but, as it was subsequently discovered wall tie corrosion could become an issue in as little as 26 years.
When wire butterfly ties corrode they break up without exhibiting any initial tell-tail signals of a structural defect. When plate-derived vertical twist or fish tail ties corrode, they have potential expand to seven times their original thickness. This expansion force is irresistible and often causes the brick walls to crack along the mortar joints, causing structural damage and affecting stability.
For more than 30 years remedial wall ties have been used for wall tie replacement in cavity walls, spawning an industry specialising in the diagnosis and remedy of cavity wall structures. Wall tie defects can be categorised as suffering from:
Manufacturers of replacement wall ties have developed a wide range of remedial products to re-tie a cavity wall, taking into account the vast combination of building materials that need to be re-connected. Substrates that need fixing to include brick, block, concrete and timber and cavity walls made from any combination of them (brick to timber, brick to block, brick to concrete etc.).
As there are no current European or British Standards appropriate to remedial wall ties or for wall tie replacement the Building Research Establishment has published BRE Digest 329 and BRE Digest 401 to give guidance on diagnosis, wall tie replacement strategy, product performance and product testing.
There are many retrofit wall ties that are designed specifically for cavity wall tie replacement, though in general they fall into three fixing types.
Remedial wall ties are not just used for wall tie replacement. They provide a useful repair option for many older buildings have a facing of attractive bricks, stone blocks or rubble masonry over a loadbearing backing wall. Such facings are often held in place only by a mortar collar joint. If the facing starts to move away from the backing it can be restrained by installing replacement wall ties.