Lack of wall ties
Over half the experiences encountered relate to the lack of wall ties. That is, either an insufficient quantity or the complete omission of ties. Next would be corrosion related decay of the tie.
Decay of wall ties
Corrosion exemplified by rust and decay of the tie. When one considers that the use of hot-dip galvanized anchors weren’t popular until the mid to late 80’s, there are a number of structures with ties that are mill galvanized or brite basic. But corrosion can also be a result of galvanic activity. The combination of different materials is the culprit in this case. With this circumstance, the less noble element is attacked such as stainless with carbon steel whereby the carbon steel is sacrificed in the presence of moisture.
Improper anchor types or sizes can be over-stressed and cause problems. Undersized anchors that are to light a gauge may have been used. Current wind loading may have changed within the buildings effective perimeter due to code changes, or new building neighbors that enhance wind speed.
Poor quality/poor workmanship
Poor quality products or construction techniques can create an unstable condition. Unfortunately, things happen and substitutions may have taken place that was less substantial then required. Other situations such as high absorption brick may have been used, insufficient or poorly sized control joints, inadequate or ineffective soft joints, suspicious mortar quality, improper fasteners to the structure for the tie, etc are examples of various quality issues.
Differential wall movement
Differential wall movement created by the differences in thermal response of the material can create an instability problem. Double wythe walls with brick headers can become unstable if the header should crack due to excessive wall movement between the inner and outer wythe. Parapets under-go major temperature swings between the outer face wall and innermost structure. If not designed properly, dislocation of the wythes is possible.
Other less obvious issues are related to environmental decay, such as acid rain. Also, chemicals used improperly to wash down the masonry can attack the existing ties over time.