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The tie in a cavity wall is a component used to tie the internal and external walls (or leaves)—constructed of bricks or cement blocks—together, making the two parts to act as a homogeneous unit. It is placed in the cavity wall during construction and spans the cavity. The ends of the tie are designed to lock into the mortar. Also incorporated into the design of the tie is means of preventing water transfer from the outer to the inner leaves. In flat ties, this can be a twist. In wire ties, this can be corrugations formed in the wire or again a twist.
Cavity 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 insulation in position. A vapour barrier may be necessary on the inner wall to prevent interstitial 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 traditionally 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 galvanized steel wire. As time has passed, many galvanized 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 adhesives.
Galvanized 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 that cavities of up to 6"(150mm) can be constructed.
Ties in a cavity wall are typically made of iron, steel, or plastic; though figures are various. Basically, a tie has ring to fasten with mortar on both end like a bow. Ties would be selected by type of masonry, the cavity width, and so on.
Typically, ties in a cavity wall are double triangular shape (like a bow), though, depending on the existence of another layer (e.g. insulation sheet) at the cavity, which fills the cavity partially, ties include retaining discs or rods.
Failure of ties is an increasing problem with cavity wall ties made from galvanized steel. It arises when the galvanizing is not of sufficient quality and the outer leaf of the cavity wall 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 to cause damage.
Since ties in a cavity wall are typically made of metal (iron or steel), they are prone to corrode over time. When metal corrodes, it expands its size, causing ties to lift up from the brickwork. Cracks caused by vertical loads leave parts of buildings vulnerable to corrosion, such as eaves and gable walls above purlin positions, or placed directly beneath openings, where the weight on brickwork is light. Over the time, cracks appear from the top of the wall and extend downward.
Cracks due to tie corrosion at the cavity wall are horizontal and tend to occur at the location of wall ties, normally 6 courses apart. The corrosion causes the walls to detach and tilt, resulting in the outer wall snapping outward. The inner wall is held in place by the added support of floor joists. At the gable wall, inner walls without these supporting joists, bow inwards. By avoiding several factors accelerating corrosion, it will last more than 60 years.
Due to its materiality of the tie, its corrosion is related to the extent of the exposure at acidic substances. The major factors of the corrosion are:
Cement-based mortar, giving an alkaline environment for cavity wall ties, has been used since the Second World War. Alkaline environment is beneficial for ties protecting from acid and procrastinating the corrosion process. Before cement-based mortar, lime-based one was used, which does not present an alkaline environment. Therefore, the majority buildings with wall tie corrosion are built before the Second World War. An alkaline degree gets weaker while exposed at acidic rain over the time.
Moreover, metal corrosion is a chemical reaction that the reaction rate is triggered by water and heat. Thus, some[ who? ] say that cavity wall insulation enhance the ability to grab water longer, so that the environment of the ties damper. Accordingly, the South or South West[ where? ] elevations warmed by the sunlight are warmer, letting ties more at risk for this type of corrosion.
Galvanization or galvanizing is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in which the parts are submerged in a bath of molten hot zinc.
Masonry is the building of structures from individual units, which are often laid in and bound together by mortar; the term masonry can also refer to the units themselves. The common materials of masonry construction are brick, building stone such as marble, granite, and limestone, cast stone, concrete block, glass block, and adobe. Masonry is generally a highly durable form of construction. However, the materials used, the quality of the mortar and workmanship, and the pattern in which the units are assembled can substantially affect the durability of the overall masonry construction. A person who constructs masonry is called a mason or bricklayer. These are both classified as construction trades.
Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH), Fe(OH)3), and is typically associated with the corrosion of refined iron.
Reinforced concrete (RC), also called reinforced cement concrete (RCC), is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having higher tensile strength or ductility. The reinforcement is usually, though not necessarily, steel bars (rebar) and is usually embedded passively in the concrete before the concrete sets.
Corrosion is a natural process that converts a refined metal into a more chemically stable form such as oxide, hydroxide, or sulfide. It is the gradual destruction of materials by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion.
Siding or wall cladding is the protective material attached to the exterior side of a wall of a house or other building. Along with the roof, it forms the first line of defense against the elements, most importantly sun, rain/snow, heat and cold, thus creating a stable, more comfortable environment on the interior side. The siding material and style also can enhance or detract from the building's beauty. There is a wide and expanding variety of materials to side with, both natural and artificial, each with its own benefits and drawbacks. Masonry walls as such do not require siding, but any wall can be sided. Walls that are internally framed, whether with wood, or steel I-beams, however, must always be sided.
A concrete masonry unit (CMU) is a standard size rectangular block used in building construction. CMUs are some of the most versatile building products available because of the wide variety of appearances that can be achieved using them.
This page is a list of construction topics.
Ferrocement or ferro-cement is a system of construction using reinforced mortar or plaster applied over an "armature" of metal mesh, woven expanded-metal or metal-fibers and closely spaced thin steel rods such as rebar. The metal commonly used is iron or some type of steel, and the mesh is made with wire with a diameter between 0.5 mm and 1 mm. The cement is typically a very rich mix of sand and cement in a 3:1 ratio; and when used for making boards no gravel is used, so that the material is not concrete.
Repointing is the process of renewing the pointing, which is the external part of mortar joints, in masonry construction. Over time, weathering and decay cause voids in the joints between masonry units, usually in bricks, allowing the undesirable entrance of water. Water entering through these voids can cause significant damage through frost weathering and from salt dissolution and deposition. Repointing is also called pointing, or pointing up, although these terms more properly refer to the finishing step in new construction.
London stock brick is the type of handmade brick which was used for the majority of building work in London and South East England until the growth in the use of Flettons and other machine-made bricks in the early 20th century. Its distinctive yellow colour and soft appearance come from the yellow local clay from which the bricks were made. London Stocks are still made in comparatively small quantities in traditional brickworks, mainly in Kent and Sussex, for heritage work, and machine-made versions are available for use where a cheaper approximation to the traditional product is acceptable. Red stock bricks are also fairly common, but only the yellow or brown coloured bricks are usually known as London stocks.
Microbial corrosion, also called microbiologically influenced corrosion (MIC), microbially induced corrosion (MIC) or biocorrosion, is "corrosion affected by the presence or activity of microorganisms in biofilms on the surface of the corroding material." This corroding material can be either a metal or a nonmetal.
A cavity wall is a type of wall that has a hollow center. They can be described as consisting of two "skins" separated by a hollow space (cavity). The skins typically are masonry, such as brick or cinder block. Masonry is an absorbent material that can slowly draw rainwater or even humidity into the wall. One function of the cavity is to drain water through weep holes at the base of the wall system or above windows. The weep holes allow wind to create an air stream through the cavity that exports evaporated water from the cavity to the outside. Usually, weep holes are created by separating several vertical joints approximately two meters apart at the base of each story. Weep holes are also placed above windows to prevent dry rot of wooden window frames. A cavity wall with masonry as both inner and outer skins is more commonly referred to as a double wythe masonry wall.
Concrete cover, in reinforced concrete, is the least distance between the surface of embedded reinforcement and the outer surface of the concrete. The concrete cover depth can be measured with a cover meter.
Structural dampness is the presence of unwanted moisture in the structure of a building, either the result of intrusion from outside or condensation from within the structure. A high proportion of damp problems in buildings are caused by ambient climate dependent factors of condensation and rain penetration. Rising Damp is a term used to describe a number of symptoms - flaky paint, hollow plaster, all of which are related to other mechanisms - usually interstitial condensation. Dry houses internally never suffer from damp issues.
Damp proofing or a Damp-Proof in construction is a type of moisture control applied to building walls and floors to prevent moisture from passing into the interior spaces. Dampness problems are among the most frequent problems encountered in residences.
Masonry veneer walls consist of a single non-structural external layer of masonry, typically made of brick, stone or manufactured stone. Masonry veneer can have an air space behind it and is technically called "anchored veneer". A masonry veneer attached directly to the backing is called "adhered veneer". The innermost element is usually structural wall, and may consist of concrete masonry, concrete, wood or metal frame.
Corrosion engineering is an engineering specialty that applies scientific, technical, engineering skills, and knowledge of natural laws and physical resources to design and implement materials, structures, devices, systems, and procedures to manage corrosion.
Concrete degradation may have various causes. Concrete can be damaged by fire, aggregate expansion, sea water effects, bacterial corrosion, calcium leaching, physical damage and chemical damage. This process adversely affects concrete exposed to these damaging stimuli.
Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. A similar galvanic reaction is exploited in primary cells to generate a useful electrical voltage to power portable devices.