Thermal cracks; causes:

Cracking in buildings is often a complex issue, influenced by factors like thermal expansion, moisture, and structural inadequacies, which can lead to both stable and unstable cracks. Understanding the root causes and implementing effective solutions, such as proper expansion joints, is crucial for ensuring the longevity and stability of a structure, preventing reoccurring damage and saving on costly repairs.

When determining a probable cause of cracking, it can be determined whether you are dealing with a stable crack ; damage that has not developed further (caused by shrinkage and creep) or an unstable crack ; damage that has developed further (e.g. due to subsidence of the foundation). In this case, the cause must first be eliminated before a proper repair can be carried out.

Causes of crack formation

Thermal length change

Materials expand as they heat up (creep) and contract as they cool (shrinkage). This creep and shrinkage due to temperature changes is also called thermal length change. Building materials must have sufficient freedom of movement to accommodate the required creep and shrinkage.

Unfortunately, this required space isn't always taken into account, and often insufficient or no expansion joints are installed. In such cases, temperature fluctuations will cause tensions that exceed the tensile forces the masonry can withstand.

The crack width in this type of cracking tends to increase over time because crumbling wall particles prevent the cracks from closing with rising temperatures.

In addition to the influence of temperature changes, creep and shrinkage can also occur in materials as a result of the influence of moisture.

Long, contiguous facades

Crack recognition:

Vertical cracks at corners
Vertical cracks along facade openings
Vertical cracks at regular intervals
Cracks that vary in width depending on temperature fluctuations
Cracks in facades exposed to large temperature fluctuations, especially south and south-west facades

Causes of damage to long, continuous facades:

No or too few expansion joints
Expansion joints in the wrong places
Exposure to temperature changes
Exposure to high moisture

Cracks at the corners

These are often cavity wall ties that are placed too close to corners or facade openings

This is a common example of prevented deformation from thermal movement.
The wall, which expands and contracts, is hindered in its movement by the cavity wall ties.
The tensile forces become too great (brick can barely absorb tensile forces), and cracks develop where the cavity wall ties are located. These cracks essentially form a natural expansion joint.

One solution for damage caused by cavity wall ties placed too close to a corner is to remove the cause (in this case, the ties) and repair the masonry. Another option is to expand the walls that are perpendicular to each other.

Combination of materials

Cracks at the meeting of different materials, such as:
- cracks at the supports of concrete lintels
- damage to joints where different materials meet (shear stresses)
Bending masonry and cracks in concrete floors (particularly poured floors), such as:
- at meetings of facade masonry with concrete floors at balcony and gallery floors.
- joint between edge beam and masonry breaks
Cracks in flat roofs and a (roof) overhang, such as:
- a horizontal crack in the gable end at the top corners of a roof edge or close to the roof structure
- a horizontal crack under the roof structure

Causes of damage due to the combination of materials

Design and/or execution error (insufficient expansion joints)
Exposure to exceptional temperature fluctuations (often south-facing facades)
Exposure to excessive moisture

Common cases

Floors or beams poured against the outer cavity wall cause lateral forces on the masonry due to expansion. This often results in bulging masonry and cracking.
Casting roofs on load-bearing walls on-site creates a situation where the roof can become extremely hot due to solar radiation, while at night, under clear skies, that same roof becomes much colder than the underlying masonry.
Temperature movements cause cracks to form, the shape of which indicates whether the masonry is uplifting due to shrinkage of the roof slab and poor quality pointing, and whether the masonry is tearing off due to expansion of the roof slab.
When the roof plate expands, lateral forces can arise, causing the facade to buck.
In high facades (of apartment buildings, for example), edge or floor beams are often installed at floor height.
During a building inspection, extensive attention is of course paid to these possible deviations.

The expansion coefficient of concrete is about twice that of brick, so changes in length due to temperature differences will also differ.

Depending on the quality of the materials, the stresses resulting from prevented deformation may or may not be absorbed by the materials. Above the edge beams, we often see shear stresses cause the joint between the edge beam and the masonry to fail, or the masonry to crack.

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