Cavity wall ties are an essential part of any building. Their job is to tie together the visible protective outer cavity of brickwork or blockwork of a building to it’s structural and load bearing inner masonry skin.
Why do cavity wall ties start to fail? In most cases this will simply be age. Over time the mortar bed between bricks or blocks that each wall tie is set into changes on a chemical level due to carbonation. Through this the mortar itself begins to attack the wall ties and cause a build-up of iron oxide (or rust as it’s more commonly known). As each tie oxidises, layers of rust are formed and expand outwards, pushing apart the mortar beds and causing visible cracks.