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Cavity wall ties and crack formation

Crack formation in masonry can be a perplexing issue, often stemming from underlying problems such as foundation subsidence, inadequate cavity wall ties, or moisture infiltration. Understanding the root causes of these cracks is crucial for implementing effective repairs, ensuring structural integrity, and preventing further damage—making it essential for homeowners and professionals alike to delve into the nuances of this topic.

Cavity wall ties and crack formation

When determining the probable cause of crack formation, we may be dealing with a stable crack ; damage that has not developed further (caused by shrinkage and creep) or an unstable crack ; damage that is developing further (e.g., due to foundation subsidence). In these cases, the cause must first be eliminated before a proper repair can be carried out.

Causes of crack formation

  1. Foundation problems
  2. Thermal cracks
  3. Drying or hardening shrinkage
  4. Insufficient or rusty cavity wall ties (discussed below)
  5. Rust formation in general
  6. Weak lintels
  7. Other constructive causes

Insufficient or rusting cavity wall ties

Bending masonry can be caused by a lateral force on the masonry or by a bending force.

  • Lateral forces are wind loads or a floor that can push a wall outwards.
  • A bending force or "moment" usually occurs because a vertical load isn't applied exactly perpendicularly. For example, a floor or roof will deflect, thus exerting a bending force on the supporting wall.
roestende-spouwanker.png

Crack recognition

  • Expansive brickwork (look along the facade!)
  • Loosening of (parts of) masonry (e.g. parapet)
  • Failure of mortar joints
  • Broken sound when the masonry is tapped with a hammer.

Design and/or execution errors

Cavity ties secure cavity walls together, providing significantly greater stiffness than two separate cavity walls.

As mentioned above, a wall must be sufficiently stiff to withstand buckling loads. If there are no, too few, or poor-quality cavity wall ties (e.g., no stainless steel), the outer and inner leaves of the cavity wall will no longer be properly connected, compromising the wall's stiffness. If the wall is then subjected to excessive buckling loads, damage will occur.

When a cavity wall tie rusts, it loses its strength and function. Rust can occur due to poor-quality materials (not stainless steel) combined with moisture in the cavity.

Homekeur-spouwanker-roest.png

⁠⁠⁠⁠⁠⁠⁠Various causes of moisture in walls

  • Construction moisture
  • Heavy rain load
  • Leaking pipes, gutters and rainwater drains
  • Rising damp
  • Moisture penetration
  • Water vapor production and thus condensation

Repair of insufficient or rusty anchors: After the cause has been addressed, repair and installation of new anchors is possible.

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