In the 1920s, houses in England began to be constructed with cavities walls. This is where two pieces of masonry are joined by wall-ties made of metal to form the exterior walls. Since the 1950s, cavity walls are now the most common design for homes.
Look the design as well as the "bond" that is formed by the bricks also look at the pattern or "bond" of the bricks. And if all bricks are laid with longer edges ('stretchers') facing you the wall is likely an 'in-cavity' wall. If the bricks have been laid out with the shorter edges ('header') facing you it's most likely an unfinished wall. This is when to replace your wall ties.
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If the wall has been rendered it is a cavity wall that typically measures between 10 1/2 and 11 inches, and an unfinished wall measures 9 and 13 1/2 inches based on the number of bricks within.
Since the mid-1980s, wall ties were made of stainless steel. However, the earlier models were not, and tend to expand and corrode when exposed to humidity. This may cause cracks in the bricks and lead to problems such as
- The brickwork bows when it is lowered
- Diagonal cracks in mortar-pointing
- Horizontal cracks in mortar beds.
Due to their lightweight, The corrosion that occurs in butterfly wire ties can cause none of the external signs. The tie can corrode all the way through, without revealing any external evidence of what's happening.
But the vertical twist tie, with its higher weight of steel, can expand to create visible splits within the bed of mortar to which they are attached.