Structurally, wall ties are essential to the stability of the normally unloaded outer leaf which can be affected by seismic events, direct wind forces and wind suction forces. Wall ties are also often used to help outer leaf masonry resist dead loads, such as those which may be associated with the fixing of company signage or awnings.

Remedial tying will be required whenever problems involving the condition and number of ties in cavity and veneer constructions are discovered.

Solid multi-leaf (or multi-wythe) walls may also require remedial tying when delamination has occurred as a result of broken headers or deteriorated mortar or to meet seismic requirements.

Suspect or inadequate connections between perpendicular walls and walls and diaphragms will often also require retrofit action.

Our remedial ties are used most commonly to address problems of:

• Veneer tie fixing inadequacy
• Wall tie failure
• Wall tie omission
• Inadequate connections between walls, timber joists and diaphragms
• Masonry and panel delamination

Common remedial problems

Veneer tie fixing inadequacy

Veneer construction generally involves the use of ties, bedded at one end into the mortar joints of a masonry veneer and fixed at the other into to an internal timber frame.

It is a very popular means of construction in Australia, with between 40% and 50% of all new domestic buildings constructed today built with a clay brick veneer tied to a timber frame.

Not surprisingly, the structural adequacy of veneer construction hinges on the adequacy of the method used to connect the tie to the frame. The problem of ensuring the adequacy of tie fixing in brick veneer construction has been well understood at least since the 1987 Edgecumbe earthquake in New Zealand.

Inspections carried out after this event indicated that veneer failure resulted in many instances from the inadequacy of the timber fixing mechanism. Prior to 1990, veneer wall tie systems commonly relied on the use of nails or staples to provide the necessary connection. During the earthquake, it appears that fixings of this type were wrenched free from the timber leaving masonry veneers vulnerable to collapse.

Wall tie failure and corrosion

The problem of wall tie corrosion has been similarly well researched following investigations into the 1989 earthquake in Newcastle. Investigations carried out after this event revealed that the failure of many masonry walls resulted from the failure of the original wall tie systems which had severely degraded over time through corrosion.

Since 1990, building codes and practices have evolved and now require the use of stainless steel and other non-corrosive materials to be used in cavity and veneer wall constructions in coastal and other zones where corrosion risks are greatest. Material requirements are listed in the joint Australian/New Zealand Standard AS/NZS2699.

Many older buildings continue to suffer brickwork collapses during seismic events and strong winds as a result of corroded wall ties. It appears that wall tie corrosion was a contributing factor to masonry collapse during the 2010/2011 Canterbury earthquake swarm.

Wall tie omission

Older buildings may contain only small numbers of wall ties at low density spacings which may be considered inadequate by modern standards.

Current Australasian standards, including NZS4210 and Australian Standard AS3700, require wall tie design specifications to consider factors such as the mass of the veneer and earthquake zoning. Thus spacing requirements may be expected to vary from one building to the next, one location to another.

Remedial tying will be required whenever the omission or inadequacy of the original wall tie system is discovered.

Separated walls and diaphragms

Mortar deterioration may weaken connections between perpendicular walls and connections between walls and timber joists and diaphragms may be inadequate. Improvements made to these is a priority for all URM retrofits.

Delaminated solid walls, render and thin panels

Solid masonry may delaminate through broken headers or deteriorated mortar. Similarly, thin panels and render may peel away from back-up materials as a result of a breakdown in the chemical bond. Delaminated masonry, render or thin panels may require remedial tying to ensure future stability.