Cavity wall tie failure is a common problem in Home Buyers Surveys in England and Wales
Originally, most brick buildings in England and Wales were constructed using a single skin wall. The two major styles of brickwork were English and Flemish Bond. The bricks in these walls were laid in alternating directions in order to resist movement in all directions.
These walls are structurally sound; however, they are not well-suited to repelling creeping fingers of moisture from the outside. The mortar can conduct moisture and eventually this can lead to penetrating damp problems.
Cavity walls – keeping England’s plaster dry since WWII
While the Cavity Wall began to be used in the UK during the 19th Century, it only became popular after the 1920s (and post-WWII in England). These walls are useful for stopping damp because they have two skins that have a gap between them (usually around 10cm). No contact between walls means access for damp. These walls are held together by metal ties – plastic ties were trialled but rejected.
Cavity wall tie failure
Cavity wall ties are prone to rust. If they are not properly protected, moisture can leach its way along the metal and cause oxidisation. This can have a number of repercussions for the homeowner.
- Expansion of the metal can cause both horizontal and vertical cracking in the brick work.
- Cracking (if left unattended) can result in destabilisation of the wall.
The properties that tend to have the worst problems with failed wall ties are those built with mild-steel “fishtail” ties (1920-1950) and those with “butterfly” ties (1964-1981). Fishtail ties can be particularly bad - sometimes actually forcing the bricks apart as they corrode away.
Assessing wall tie failure
A Chartered Surveyor conducting a Home Buyers Survey will assess the brickwork carefully for any signs of cracking. If they suspect that the wall ties may be failing, they will often advise that a specialist be contacted.
Some companies who specialise in wall tie failures will drill into the walls and use an endoscope or borescope to assess the tie condition. The Building Research Establishment Digest 401 suggests that this method is insufficient. An assessment should not just tell you whether a tie is failing, it should tell you by how much. This can give you an accurate measure of how long you have till major action needs to take place. Often it can be years. The only way to assess this is to remove some of the bricks.
How to prevent wall tie failure
Replacing wall ties is a major structural renovation. Better to prevent them rusting, or, if they are just beginning to corrode, to slow down the process. The best way to do this is to attend to the external surface’s rendering and pointing. Healthy render and mortar will prevent your wall ties from failing you for a long time.