TECHNICAL BULLETIN
ISSUE 37
APRIL 2021
CAVITY WALL TIE FAILURE A DAY ON THE TOOLS CHRISTOPHER MORAN, BA (HONS) ASSOC RICS, DIRECTOR, CHRISTOPHER MORAN RESIDENTIAL SURVEYING & SAVA GRADUATE
In this article, recent Sava graduate Chris Moran shares his experience shadowing the award-winning company ‘Brick-Tie Ltd’. Chris spent the day with Brick-Tie technicians carrying out cavity wall tie replacement on a 3-bedroom semi-detached house in Sheffield. This article provides a useful overview of cavity wall tie failure, identifying factors, and how professional experts go about replacing failed cavity wall ties. Chris also provides some useful tips for students struggling to find mentoring opportunities during times when it has proven difficult for many students to gain practical shadowing experience.
What is cavity wall tie failure?
Cavity wall tie failure is a failure of (or corrosion to) the ties used to hold the internal and external walls making up a cavity wall. The main cause of failure is the rusting of metal ties; although, there can be other causes, such as failure to properly bed the tie in the mortar joint, poor quality mortar reducing the bond between tie and mortar, or not installing the requisite number of ties.
Figure 1: Rusting cavity wall tie
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The following factors play a part: •• Rust leading to disintegration resulting in possible wall collapse. •• Rust expansion (up to 600% the size of the original tie!). •• Cracking (normally horizontal) and structural distortion in the walls. •• Cracking leading to reduced weather resistance of the wall and an increase in corrosion. •• Corrosion of wire ties can cause total failure without the warning tell-tale signs of cracking. This is
