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A cavity wall is formed from two layers of masonry seperated by a space. These two masonry layers, commonly known as the inner and outer, are often referred to as leafs and they are usually held together with cavity wall ties.
Cavity wall ties have been used as part of building construction to hold the inner and outer leafs of a wall together since around 1850. Without cavity wall ties, the increasing weight of masonry above would cause the two leafs to move apart.
Cavity wall construction became common from 1940's and wall ties produced before 1981 have a history of premature failure and every year many homes across the UK suffer from cavity wall tie corrosion as a result of corrosive (black ash) mortars, premeable lime mortars, exposure to wind-driven rain, coastal locations, substandard galvanising on the tie and, on some of the early cavity wall ties, no protection from corrosion. Without these conditions, steel wall ties still corrode, but at a much slower rate.
If corroded wall ties are left untreated, the masonry can bulge or crack and, in some cases, the building becomes unstable. It is not uncommon for entire developments to have the same problem, as all properties would be built at the same time.
If you suspect your property is suffering from corroded wall ties or are concerned about the stability of your property, give us a call on 0800 0121 437 to request a cavity wall tie survey with one of our expert surveyors.
Early fishtail cavity wall ties are long strips of iron or steel that are placed into the cavity wall during construction to hold the internal and external walls together. From the early 1920s, the twisted wire Butterfly tie started to be used. Placed horizontally across the two walls and secured in place with mortar these strengthen the wall. Their design prevents moisture running from the exterior wall to the internal wall and are essential to the safety and stability of the wall. Without wall ties or ones which are corroded, large sections of brickwork such as gables can be affected by wind suction and collapse.
Cavity wall ties were initially made from iron or steel, however, under damp conditions, both iron and steel corrode. To prevent deterioration, wall ties were galvanised with a protective zinc coating. Over time, the galvanised protective layer can break down leading to wall tie failure. The first British standard wall tie with a defined zinc coating did not arrive until 1945 and was improved in 1981.
When fishtail wall ties corrode, they start to expand in size forcing the outer leaf to crack along the mortar joint. Wire Butterfly ties tend to corrode and snap without expanding, so the first sign of a problem may be bulging in the wall. Most Butterfly wall ties are expected to have a design life of around 35 years but this can be much less in certain conditions. In modern building construction, cavity wall ties are made from stainless steel to prevent corrosion.
Many homeowners may not spot cavity wall tie failure until the signs of cracking or bulging begin to appear. Similar damage can occur if wall ties are not installed at the correct horizontal and vertical spacings or when wall ties have been left out of parts of a structure.
Horizontal Cracks - in the mortar, often at a high level, caused by the expansion of corroded wall ties on the external leaf
Bulging Brickword - caused by snapped wall ties, which can make your property unstable
Internal Cracks - internal cracks caused by the expansion of corroded wall ties are much rarer
Cracks to the render - vertical cracking to render
Lifting of roof edges - The roof load is carried by the inner leaf, but as corroded fishtail wall ties expand and crack the mortar, the outer leaf takes the load and the roof may be forced upwards, or the gable ridge rises
Our surveyors will carry out a thorough survey of your property in accordance with BRE Digest 401 to establish whether there is an issue and highlight if any remedial work is required. Using diagnostics tools such as an endoscope and metal detection equipment, our experienced surveyor will identify and inspect a selection of wall ties, identify any cracks or defects to the brickwork and provide advice alongside a quote on effective treatment.
If a problem with wall tie corrosion has been identified, our surveyor will design a bespoke treatment plan to fit your needs, and our specialist technicians will treat the problem by locating and replacing any corroded wall ties. This treatment involves;
- Drilling holes in appropriate areas of brickwork, using low impacting drills to reduce damage to the masonry.
- Install new non-corroding stainless steel wall ties at the correct density and then pull test the correct number. Our surveyor will discuss and recommend the best type of cavity wall ties for your property depending on the type and condition of the masonry.
- In most cases the corroded wall ties are isolated to prevent further damage, but may need to be removed.
- Cover drill holes to match the existing wall appearance to preserve the facade of your property.
Upon completion, all work carried out by our team is covered by our 25-year guarantee, giving you peace of mind that should a problem occur in the future you are covered. Even if you decide to sell your property we will be able to transfer your guarantee to the new owner.
If you would like to know more about our services or if you think you have identified a potential problem in your property, then give us a call on 0800 0121 437 to arrange for one of our qualified surveyors to come and visit your property.
If you are concerned with the stability of your property and would like expert advice, give us a call. Our in-house property team are on hand to take your call and answer any queries you have and can arrange to book you in for a property inspection with one of our qualified surveyors. To get in touch, give us a call on 0800 0121 437 or complete our online form below for a member of our team to get in touch.