Wall Tie Replacement
Wall Tie Replacement
Wall ties are used to join the internal and external walls (or leafs) of a cavity wall and are installed during construction. Over time these wall ties can corrode and require replacement – particularly where ungalvanised or inadequately protected steel wall ties have been used. The expansion caused by this type of corrosion can force apart mortar joints, causing cracking of masonry. Other symptoms include bulging of walls and the lifting of roof edges. In severe cases wall collapse has even been reported.
Wall tie corrosion is particularly common in buildings in coastal areas (due to salt-laden driving rain) and in masonry constructed using corrosive black ash mortar. Because most buildings will outlast the life expectancy of the wall ties installed during construction, wall tie replacement will be necessary at some point for most buildings constructed using cavity walls. Replacement may also be necessary if the original ties were installed incorrectly — too few ties, the wrong type, or poor site control during installation.
Replacement Wall Ties
Wall tie replacement is carried out using special types of wall tie developed specifically for use on existing walls. Three types are typically used:
- Mechanical-mechanical wall ties
- “Screw-in” helical wall ties (Driveties)
- Resin-resin helical wall ties
Choosing which type to use depends on a number of factors including the type of masonry, whether the cavity contains insulation material, and fire performance requirements. Replacement ties are supplied in a variety of lengths as cavity widths can vary considerably.
Wall Tie Replacement Procedure
BRE Digests 329 and 401 give detailed advice on suggested procedures. Broadly speaking, the procedure can be divided into five elements:
- Investigation — collecting information about the type and condition of masonry, cavity width, and existing wall ties.
- Isolation / removal of existing wall ties depending on condition.
- Specification — choice of remedial wall tie type, density and layout.
- Installation of replacement wall ties.
- Quality control — visual checks, torque testing, etc.
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