Cavity Wall Tie Failure: Inspection, Diagnosis, and Repair

Cavity wall ties hold the inner and outer leaves of a cavity wall together. Galvanised ties from the 1920s–1980s corrode silently, and the first sign is often visible bulging of the outer leaf — by which point repair is urgent.

Why wall ties fail

Pre-1980s galvanised steel ties have a finite life — typically 30–60 years. Corrosion thins the tie until it loses load-carrying capacity, and the expanding rust splits the mortar joints they sit in.

Symptoms

• Horizontal cracks in mortar joints at regular vertical intervals (~450mm)
• Outer leaf bulging visibly
• Mortar staining or rust streaks
• Inner skin pulling away from outer (visible at openings)

Inspection methods

Metal detector survey

Maps existing tie locations and condition without invasive work.

Endoscope (borescope) inspection

Small holes drilled in mortar joints allow visual inspection of cavity and tie condition.

Tie extraction

A sample of ties removed and assessed under microscope. Most reliable for life-expectancy assessment.

Remediation options

Replacement ties

New stainless steel ties drilled through the wall and resin-anchored or mechanically fixed. Standard repair.

Helical ties

Stainless steel helices driven into pre-drilled holes. Fast install, no resin curing time.

Brickwork stitching

Where cracks have opened, stainless helical bars bedded in cut mortar joints reinforce and tie the masonry.

Cost

• Inspection survey: R8,000–R18,000
• Replacement ties: R500–R900 per tie installed
• Typical semi-detached house full replacement: R70,000–R150,000

When to act

If your house was built 1900–1980 and has any visible bulging, cracking at regular spacing, or movement, commission an inspection. Untreated, bulging walls can fail — and the failure is rarely graceful.

MCFAR assesses wall tie condition and specifies repair.

Frequently Asked Questions