Environmental reasons for cracks in external wall insulation mortar
Environmental causes of cracks in external wall insulation mortar
1. Deformation caused by deformation of wall structure: uneven spacing of the foundation is too large, and the distance between the wall and the corner of the brick wall is not increased, the door and window openings are too large, and the deformation joint is improperly set, which makes the wall strong, rigid and stable. Deformation of the structure causes structural deformation cracks, resulting in cracking of the mortar layer.
2. Inappropriate selection of raw materials and ingredients
1 The cement mortar is simply blended with gypsum or lime powder. Although the workability is improved, the strength of the mortar is reduced, the shear resistance and the bond strength are also reduced, and the shell (empty drum) is easily cracked.
2 Some construction units use better cement and aggregates for the beam slabs and columns of the building during construction. It is wrong to use low-grade cement and fine aggregates when painting without considering structural safety, resulting in cement mortar. The contraction is too large and cracks.
3. Factors that change temperature and humidity
1Exterior wall cement mortar is exposed to the air for a long time, and often expands or contracts due to changes in humidity. Humidity deformation is related to the change of water content of cement mortar and the shrinkage rate. In the deformation caused by humidity, the expansion value is 1/9 of its shrinkage value, and the dry shrinkage rate of cement mortar is a curve of reversed decline. The initial shrinkage is rapid and the time is gradually slowed down. This shrinkage is irreversible. The shrinkage caused by humidity changes is a reversible process of dry and wet cycles. When the shrinkage stress is greater than the tensile strength of the mortar, the mortar inevitably produces cracks.
2 Temperature changes cause building materials to expand or contract, but different materials have different temperature coefficients and deformation stresses. Thermal expansion produces temperature stress at the interface. Once the temperature stress is greater than the tensile strength of the cement mortar, the material will be relatively displaced, resulting in cracks in the mortar. Most of the external wall cement mortar is exposed to sunlight, the temperature of the mortar layer may greatly exceed the temperature, even more than double the outdoor temperature, plus the change of sunshine time and the temperature difference of the cold winter heat, the temperature stress generated is large. Wall cement mortar produces temperature shrinkage cracks. Although the cracks generated by temperature stress are relatively small, the repeated cracks will continue to expand.
In summary, there are many reasons for the cracks in the external wall cement mortar. Except for the specification and improvement in construction, proportioning, material selection and wall, effective measures can be taken from the cement mortar itself to improve the construction. Wall quality.