The Technical stuff…Why Cavity wall
Originally in England most brick buildings were constructed using single skin walls. The bricks were laid in alternating directions to resist movement in all directions. These walls while remain structurally sound are not very well suited to repelling moisture from the outside. Also the mortar between the bricks can conduct moisture and will and does lead to penetration damp problems.
Cavity Walls…. Dry plaster since WWII
Cavity walls were first used in the early 19th century, however they only became after the 1920’s basically post World War II England. Walls were now useful for stopping damp as they comprised of two skins with a gap between (around 10cm). As these now ‘cavity’ walls have no contact between the inner and outer leaf this means no access for damp also.
And now …….the wall ties
The inner and outer leaf of the cavity walls require a link to hold the two together to stop the ‘bowing’ or the walls or wall movement. Cavity walls are held together with metal restraints or ties to enable a link (for strength) to be retained while at the same time leaving a cavity to prevent possible damp.
|Fishtail wall ties (1920 – 1950)||Butterfly wall ties (1964 – 1981)|
Why do wall ties fail in cavity walls?
The signs . . .
Expansion of he metal can cause both horizontal and vertical cracking in the brickwork cracking left unattended can result in destabilization of the wall cavity wall ties are prone to rust if not properly protected, moisture can filter its way along the metal causing oxidation.
|Horizontal Crack||Step Crack||Wall bowing|