Weak Lintels: Causes and Repair of Cracking

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

⁠⁠⁠⁠⁠⁠⁠At the location of facade openings:

• Deflection of the lintel, sagging of the upper sills
• Tapering cracks from the corners at the lintel support
• The triangular or strip-shaped detachment of overlying masonry
• Crack in the center of the bottom of the brickwork
• Cracked and fallen joints above a lintel

• In a span in masonry, the span will naturally form a compression arch.
• A straight span in the masonry is only possible for small dimensions. If this is implemented, it is preferable to install a so-called roll course that begins diagonally in the wall at the sides. This creates a slightly wedge-shaped joint in the roll course. If a brick threatens to sink out of this roll course, it will remain wedged in place by this wedge shape, creating lateral pressure.
• In addition to an arched span in masonry, the masonry can also be supported by a beam, or lintel.
• A design error or execution error is often the cause of such damage.
• In order to support the overlying masonry, a lintel must be of sufficient strength (calculated for weight and span).
• If a lintel is inadequate or insufficiently dimensioned it will sag under the weight of the overlying masonry (In practice, these cracks usually run from the corners in a triangular shape diagonally upwards).
• When beams or lintels sag, the masonry will be subjected to the greatest tension load in the middle and will therefore tend to crack at the bottom.

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