Wall Tie Installation History
Cavity walls incorporating metal wall ties have been used since the beginning of the nineteenth century but it was in the 1880’s building boom that produced large numbers of cavity construction dwellings. From 1945 cavity wall construction became the normal for houses and many other buildings.
The early metal wall ties produced mainly from wrought iron or cast iron performed satisfactorily but in more recent years mild steel wall ties have been used and despite galvanizing or bitumastic treatments have been found to suffer from wall tie corrosion. A British standard was produced in 1945.
The estimated life of these mild steel wall ties is appreciably less than the sixty year life expected. The 1945 standard was relaxed in 1964 and 1978. And in 1981, when the extent of the problem was registered the British standard was amended to triple the zinc coating thickness on a wire tie.
A number of cases of distress of cavity wall attributable to wall tie failure have occurred in the United Kingdom and it is now clear that the problem could eventually affect all the cavity wall structures built before 1981, some 10 million dwellings and will not in future be confined only to cases of poorly made ties.
Wall tie failures reported to the Building Research Establishment include inferior coatings of bitumen, insufficient zinc galvanizing on mild steel, aggressive mortars (particularly black ash), exposure to marine climates and permeable mortars such as lime that permits rapid carbonation.
It is estimated that over 3 million houses of cavity wall construction were built before the introduction of the 1945 standard. Between 1945 and 1964 an additional 3 million houses were built to the British standard BS 1243 – 1945 with wire tie life expectancy of 15 to 31 years and a stripe tie life expectancy 31 to 61 years. From 1964 to 1986 over 4 million houses were built to the lower British standard with a wall tie life expectancy of 23 to 46 years.
It was estimated in the 1986 survey of English houses that around 12 million properties exist with cavity walls of which the number requiring some repairs to wall structures is approaching one million.
Wall Tie Replacement Survey
Wall tie corrosion is a big problem affecting Period houses today. This type of corrosion causes numerous building issues, trapped moisture in poor exposed mortar joints. The signs of these faults could be external bricks cracking and lifting mortar beds.
Our surveyor will be happy to attend and give on sight advice and a written report if required for a Mortgage on the condition of a property’s wall ties.
Types of Wall Ties
- Cast and wrought iron wall ties are usually of heavy section and cannot easily be cropped or bent back and must be removed.
- Stone and slate wall ties have poor mechanical grip and are likely to snap with movement. Slate and ceramic wall ties do not corrode or laminate and therefore need not be disturbed.
- Brick and terracotta wall ties act as a cold bridge and transmit moisture and are likely to perish.
Metal ties have been made from cast iron, wrought iron, mild steel, copper and more recently stainless steel. Although the design is more practical than their predecessors most have the inherent enemy rust despite being galvanized or bitumastic coated.Mild steel fish tail wall ties require them to be isolated or removed from the mortar joint.
Butterfly wall ties are both heavy or light weight and only light weight wall ties in 12mm or thicker mortar joints can be left undisturbed. Heavy duty wall ties and all wall ties in mortar joints less than 12mm must be isolated or removed.
Copper wall ties are not found frequently; they are durable and have a long life.
Be Dri Customer Service
Don’t be damp Be Dri call us today and let us help you with any of your wall tie replacement, damp proofing, woodworm treatments, repointing brickwork and wet and dry rot issues.
It’s free to call and costs nothing to ask your questions.