Tie (cavity wall)
Encyclopedia
The tie in a cavity wall
is used to tie the internal and external walls(or leafs) constructed of bricks or cementatious blocks together. It is placed in the cavity wall during construction and spans the cavity. The ends of the tie are designed to lock into the cement. Also incorporated into the design of the tie is means of preventing water transfer from the outer to the inner leafs. In flat ties this can be a twist. In wire ties this can be corrugations formed in the wire or again a twist.
Cavitity walls often have insulation in the cavity which may either partially or fully fill the cavity. Partial fill insulation systems require specialized ties or clips to keep the isulation in position. A vapour barrier may be necessary on the inner wall to prevent intersticial condensation. This is often incorporated into the cavity wall insulation
system.
The spacing of ties is laid down in building regulations, though there may be variations with specialised blocks. Additional ties are used around window and door openings
Improper installation may lead to water damage or fungus
formation within the cavity, leading to structural and health hazards.
Ties are exposed to water and chemical attack from cement
. They were traditiionally made of galvanized steel, the fishtail tie being the most common. On high quality work ties were occasionally made of bronze
. In the mid-twentieth century wire ties were widely used, again made from galvanised steel wire.
As time has passed many galvanised steel ties have deteriorated due to moisture in the outer leaf of brickwork. The corrosion may force apart the cement joints and even result in the collapse of walls if no remedial action is taken. Any cracks appearing in cavity walls dating from the twentieth century need to be investigated before irremediable damage ensues. Horizontal cracking is especially suspect.
Failed ties have to be isolated and substitute specialist ties installed by drilling through inner and outer leaves from outside the building. The replacement ties may be fixed mechanically or with special adhesive
s.
Galvanised steel ties are no longer in use for this reason. For a brief period, plastic ties were used but were not satisfactory. Modern practice is to use stainless steel
ties.
Cavity walls were traditionally spaced 2"(50mm) apart. Due to the need for thicker insulation in exterior walls these days, a range of longer ties are now available so than cavities of up to 6"(150mm) can be constructed.
allows water penetration, usually due to porous brick/blockwork. If the tie rusts, the swelling effect may cause horizontal, external cracks to appear in the wall. Frost action can swiftly enlarge these cracks.
Cavity wall
Cavity walls consist of two 'skins' separated by a hollow space . The skins are commonly masonry such as brick or concrete block. Masonry is an absorbent material, and therefore will slowly draw rainwater or even humidity into the wall. The cavity serves as a way to drain this water back out...
is used to tie the internal and external walls(or leafs) constructed of bricks or cementatious blocks together. It is placed in the cavity wall during construction and spans the cavity. The ends of the tie are designed to lock into the cement. Also incorporated into the design of the tie is means of preventing water transfer from the outer to the inner leafs. In flat ties this can be a twist. In wire ties this can be corrugations formed in the wire or again a twist.
Cavitity walls often have insulation in the cavity which may either partially or fully fill the cavity. Partial fill insulation systems require specialized ties or clips to keep the isulation in position. A vapour barrier may be necessary on the inner wall to prevent intersticial condensation. This is often incorporated into the cavity wall insulation
Cavity wall insulation
Cavity wall insulation is used to reduce heat loss through a cavity wall by filling the air space with a porous material. This immobilises the air within the cavity , preventing convection, and can substantially reduce space heating costs.During construction of new buildings, cavities are often...
system.
The spacing of ties is laid down in building regulations, though there may be variations with specialised blocks. Additional ties are used around window and door openings
Improper installation may lead to water damage or fungus
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
formation within the cavity, leading to structural and health hazards.
Ties are exposed to water and chemical attack from cement
Cement
In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...
. They were traditiionally made of galvanized steel, the fishtail tie being the most common. On high quality work ties were occasionally made of bronze
Bronze
Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...
. In the mid-twentieth century wire ties were widely used, again made from galvanised steel wire.
As time has passed many galvanised steel ties have deteriorated due to moisture in the outer leaf of brickwork. The corrosion may force apart the cement joints and even result in the collapse of walls if no remedial action is taken. Any cracks appearing in cavity walls dating from the twentieth century need to be investigated before irremediable damage ensues. Horizontal cracking is especially suspect.
Failed ties have to be isolated and substitute specialist ties installed by drilling through inner and outer leaves from outside the building. The replacement ties may be fixed mechanically or with special adhesive
Adhesive
An adhesive, or glue, is a mixture in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials...
s.
Galvanised steel ties are no longer in use for this reason. For a brief period, plastic ties were used but were not satisfactory. Modern practice is to use stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
ties.
Cavity walls were traditionally spaced 2"(50mm) apart. Due to the need for thicker insulation in exterior walls these days, a range of longer ties are now available so than cavities of up to 6"(150mm) can be constructed.
Cavity wall tie failure
This is an increasing problem with cavity wall ties made from galvanised steel. It arises when the galvanising is not of sufficient quality and the outer leaf of the cavity wallCavity wall
Cavity walls consist of two 'skins' separated by a hollow space . The skins are commonly masonry such as brick or concrete block. Masonry is an absorbent material, and therefore will slowly draw rainwater or even humidity into the wall. The cavity serves as a way to drain this water back out...
allows water penetration, usually due to porous brick/blockwork. If the tie rusts, the swelling effect may cause horizontal, external cracks to appear in the wall. Frost action can swiftly enlarge these cracks.