Wall ties are the unseen elements of the cavity walls. Incorporated inside the wall, they are inserted by the construction worker during the construction of the wall. They are essential for the safety and stability of cavity walls. Here’s the reason.
If you see an apartment built from stone or brick, constructed after the start of the world war, then you are likely looking at a cavernous wall with wall ties. A wall that isn’t able to stand up straight without wall tie-ups within.
There are two components to the cavity wall, the leaf inside and the leaf that is external. Sometimes, they are referred to as the outer skin and inner skin brickwork. The reason wall ties are important is because of the thickness of outer skin in relation to its height the ratio between the wall’s thickness and its height is known as the ‘slenderness’. Engineers who study structural engineering calculate this by taking the walls “radius of gyration”, however, we’re not structural engineers and will make use of the rough guide which is more straightforward. ….
For instance, if the wall thickness is 110mm (the average thickness for a typical brick) and 1 centimetre high, it would have the ratio of 1:9 for slenderness The wall is 9 times taller than its thickness or its thickness is a 9th of its height (both are the same). Thus, a typical home wall, say 5 metres high would have a slenderness ratio of 1:45. This is a large slenderness ratio. This implies that a wall at that height and so thin without support can be crushed by a breeze or by a child’s hand. Consider the famous game Jenga in which you alternately place the wooden pieces on top one the other. It becomes extremely tough as the column increases and becomes unstable because of the growing ratio of slenderness.
This is the case for any cavity wall and is why wall ties are crucial.
What is the inside skin? This is made with the same substance, mostly block or brick, but occasionally timber too. It also has the same slenderness ratio in the event that it was independent of its outer skin. But, the inner skin has a lot of support. This counteracts the slenderness, and renders it more rigid. This includes: the floor joists and other that are anchored to the ceiling joists that could also brace it; the roof too, that is built upon it , and in modern houses, secured to it. These elements provide horizontal “lateral restraint’.
There are also the walls that separate rooms. They secure the skin’s interior and provide the vertical “lateral restraint.
The weight of the flooring, roof and so on can also support the skin. Consider this: if you constructed an uninspiring wall with a height of say, ten bricks with no mortar, and sitting on it the child would not be able to move the wall and this would provide stability. Stand up while the child pushes and the wall will fall easily.
Thus, with a cavity wall we get a solid box-like structure with loads that provide greater stability. However, it’s encased within a very unstable, independent structure that has its own weight and there is no bracing to provide an lateral limit. If you were to tear off the exterior walls of a cavity and the structure behind it would not look nice as damp might be able to enter, but it wouldn’t fall.
Wall ties are the lifeline to our fragile outer skin. They are placed at regular intervals both vertically and horizontally, cavity wall ties draw a bit of the stability of the house and transfer that stability to the skin of the wall. In effect, the outer skin is a part of the total thickness of the wall. This reduces the slenderness of the whole wall by one mile. And hey you have a sturdy wall that will last for several years.
Wall ties are generally made of metal, however plastic, and even composite materials are also being used. They must be strong enough to hold the exterior leaf in place, however they also have been made to permit a slight motion, to ensure that the leaf will move a little as it warms to cool and warms.
Wall Tie Corrosion is the huge remnants left behind from the years in the construction of cavity walls using mild steel wall tie. Nowadays, the material that is used to construct wall tie are stainless steel however, for a while it was made of mild steel with either an acrylic film or zinc coating to protect. These coatings don’t last long and when wall ties begin to corrode it is one of structural nature and needs to be addressed.
