In building construction, the use of thermal insulation mortar is becoming more and more widespread. However, thermal insulation mortar in the use of the process will often appear cracking phenomenon, affecting the overall quality and beauty of the building. So, what are the reasons that lead to the cracking of thermal insulation mortar? This paper will analyze in detail from the mortar and substrate deformation inconsistency, dry shrinkage deformation and temperature deformation.
Analysis of mortar and substrate deformation inconsistency
Self-generated volume deformation
The cementitious materials in mortar will undergo volume changes during the hydration reaction, especially cement-based mortar, the hydration process is usually accompanied by shrinkage. The base material, on the other hand, is generally a material that has already completed its reaction and has minimal volumetric deformation. This difference in self-generated volume deformation can lead to stresses between the mortar and the substrate, which can trigger cracking.
Dry shrinkage deformation analysis
Different Drying Deformation Rates
Mortar and substrate have different drying deformation rates due to the different materials. Mortar loses a lot of water during the drying process, resulting in significant shrinkage deformation, whereas the substrate has less shrinkage deformation due to its low initial moisture content. This inconsistency in the drying shrinkage deformation will result in higher stresses in the mortar layer, leading to cracking.
Different initial water content status
The mortar is in a water-saturated state at the time of application, while the substrate may be dry or have very little water content. This difference in initial state can cause the mortar to lose more water during the drying process, resulting in greater drying deflection. At the same time, the substrate may absorb water from the mortar, further exacerbating the mortar’s shrinkage deformation.
Different environmental effects
The mortar layer is exposed to the external environment and is more affected by environmental changes and dries faster. Substrates, on the other hand, are usually located internally and are less affected by the environment. This difference in drying speed will lead to unsynchronized drying and shrinkage deformation of the mortar layer and the substrate, thus triggering cracking.
Temperature deformation analysis
Different coefficients of thermal expansion of materials
The thermal expansion coefficients of mortar and substrate materials are different, and temperature changes will lead to different deformations of the two. When the temperature rises, if the coefficient of thermal expansion of the substrate is greater than that of the mortar, the substrate will expand more than the mortar, which will cause the mortar to be tensile and produce cracks. Conversely, when the temperature decreases, the free contraction of the mortar is greater than that of the substrate, and the mortar layer will similarly be subject to tension and cracking.
Interaction between mortar and substrate
In summary, there is inevitably a deformation difference between mortar and substrate. This deformation difference will produce interaction force, so that the mortar layer will be subjected to additional stress, which will eventually lead to cracking. Therefore, in actual construction, effective measures should be taken to reduce the deformation difference between mortar and substrate, thus reducing the possibility of mortar cracking.
Preventive measures
In order to prevent the insulation mortar from cracking, the following measures can be taken:
Selection of appropriate materials: Select mortar and substrate with similar deformation properties to reduce the difference between self-generated volume deformation and dry shrinkage deformation.
Control the construction environment: avoid construction under extreme weather conditions, and keep the drying speed of the mortar layer consistent with the substrate.
Reasonable proportioning: add appropriate amount of fiber and shrinkage reducer in the mortar to enhance the anti-cracking performance of the mortar.
Construction process: in the construction process, to ensure that the mortar and the substrate are fully bonded, to avoid the generation of voids and reduce the difference in deformation.
The above measures can effectively reduce the risk of cracking of insulation mortar and ensure the quality and durability of the building.