*Cavity Wall Ties

Question 1

According to BRE, what buildings are at risk of cavity wall tie failure?

Answer 1

Building cavity ties built before 1981, when the standards on cavity wall ties increased. Also, until 1970s wall ties were a twisted butterfly type

Question 2

What factors will affect wall tie corrosion?

Answer 2

• Humidity (interstitial condensation)
• Rain fall (penetrating damp)
• Chlorides
• Sulphar dioxide
• Changes in PH (carbonation, carbonic acid)

Question 3

What equipment would you use to detect the location of wall ties?

Answer 3

• Wall tie detectors - hand held metal detectors

- Borescope (to see within the cavity)

Question 4

What is the typical correct spacing for wall ties within a cavity wall?

Answer 4

• Every 6th course
• 900mm centres horizontally
• 300mm away from windows/ openings

Question 5

What are the symptoms of cavity wall tie failure?

Answer 5

• Bowed or cracked brickwork
• Cracking that follows lines of wall ties (every 450mm horizontally)
• Random bulges
• Rust staining

Question 6

How can wall tie failure be rectified?

Answer 6

Removal of old ties, then replace with new using resin grout and mechanically fixed wall ties (polyurethane foam can be injected into the cavity to form a bond between the two leafs), and then repairs to the external walls