The Technical stuff…Why Cavity wall
THEN – pre wall ties
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.
NOW – with wall ties
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.
The two original types of mild steel wall ties (plastic was initially tried and rejected).
Modern remedial wall tie below– used to replace the above wall ties.
Modern cavity remedial wall ties are composed of corrosion resistant Stainless Steel tie bars with Neoprene sleeves. The tie features a unique ‘tall-nut’ which once tightened, forces the inner leaf Neoprene sleeve to open and grip in the masonry.
Why do wall ties fail in cavity walls?
Cavity wall ties are prone to rust if not properly protected, moisture can filter its way
along the metal causing oxidation of the original wall tie.
Properties which tend to have the worst failed wall ties were build with the mild-steel ‘fishtail’ ties (1920 –1950) and butterfly (1964-1981) Fishtail ties can be particularly bad on occasion forcing the bricks apart as they corrode away.
The signs . . .
- Expansion of the metal wall tie can cause brickwork to crack both horizontal and vertically
- 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.
How we fix cracks and failed wall ties ……
This is Rem Tie at work….
Possible Extra – Crack Stitching
If there is a step in the cracked wall, this will need a horizontal inserted resin bonded Helifix bar as well as wall ties either side of the step crack.