Wall Tie Failure
Spotting the Signs
Defects often manifest themselves in the bowing, leaning or bulging of walls as the outer wall is no longer connected to the main structure of the property. Vulnerable areas of masonry include gable apexes and panels between window openings.
As corrosion of the wall ties set in, they build up iron oxide (rust) layers, which occupy a greater volume than that of non-corroded steel. In some instances, particularly when wire wall ties have been used, this increase in volume is accommodated within the mortar bed as the cavity tie erodes, leaving little sign that the outer façade is free-standing and the walls un-supported, other than the wall may appear bulged or out of plumb as it is restrained only by the strength of corners and return walls.
In other cases, particularly where sheet steel ties of greater mass have been used in less forgiving mortars, the iron oxide build up may have a theoretical fourfold expansion in volume. Such irresistible ‘expansion’ may have the effect of lifting the masonry above each line of wall ties, producing a pattern of horizontal cracks along the bed joint courses that host the ties.
Another telltale sign is at the apex of a roof, which may be lifted higher than the rest of the roof by the masonry, which has vertically expanded, underneath.
A boroscope or endoscope can be inserted into the cavity to investigate the condition of the existing ties.