Environmental Causes of Cracks in Thermal Insulation Mortar of Exterior Wall


Release time:

2020-04-20

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Cracks caused by deformation of wall structure: uneven settlement of foundation, too large spacing between transverse walls, no reinforcement at corner stress concentration of brick wall, too large door and window openings, improper setting of deformation joints and other reasons cause structural deformation cracks of wall due to insufficient strength, rigidity and stability, resulting in cracking of mortar layer.

Environmental Causes of Cracks in Exterior Wall Thermal Insulation Mortar

 

1. Cracks caused by deformation of wall structure: uneven settlement of foundation, too large spacing between transverse walls, no reinforcement at corner stress concentration of brick wall, too large door and window openings, improper setting of deformation joints and other reasons cause structural deformation cracks of wall due to insufficient strength, rigidity and stability, resulting in cracking of mortar layer.

 

2. Improper selection of raw materials and ingredients

① cement mortar ingredients in the simple incorporation of gypsum or lime powder, although the workability is improved, but the mortar strength decreased, shear strength and bonding strength also decreased, easy to shell (hollowing) cracking.

② Some construction units in the construction of the building's beams, columns, such as the selection of better cement and aggregate, etc., mistakenly believe that the painting does not need to consider the structural safety issues, the use of low-grade cement and fine aggregate, resulting in cement mortar shrinkage and cracking.

 

3. Factors of temperature and humidity changes

Exterior wall cement mortar long-term exposure in the air, often due to changes in humidity expansion or contraction. Humidity deformation is related to the change of water content and dry shrinkage of cement mortar. In the deformation caused by humidity, the expansion value is 1/9 of the shrinkage value, the drying shrinkage rate of cement mortar is a reverse curve, the initial drying shrinkage is rapid, and the time will gradually slow down, this shrinkage is irreversible. The shrinkage caused by humidity change is a reversible process of dry-wet cycle. When the shrinkage stress is greater than the tensile strength of the mortar, the mortar will inevitably produce cracks.

The temperature change causes the building material to expand or contract, but different materials have different temperature coefficient and deformation stress. Thermal expansion produces temperature stress at the interface, and once the temperature stress is greater than the tensile strength of cement mortar, it will cause relative displacement of the material, resulting in cracks in the mortar. Most of the external wall cement mortar is exposed to the sun, and the temperature of the mortar layer may greatly exceed the air temperature, even more than double the outdoor temperature. In addition, the temperature stress generated by the change of sunshine time and the temperature difference between cold and hot winter will cause temperature shrinkage cracks in the external wall cement mortar. Although the cracks generated by temperature stress are relatively small, such repeated cracks will continue to expand.

 

To sum up, there are many reasons for the cracks in the external wall cement mortar, in addition to the construction, ratio, material selection, wall and other aspects of standardization, improvement, from the cement mortar itself can take effective prevention and control measures to improve the construction of external wall quality.

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