The reason analysis and solutions for insulaiton mortar cracks
Author：ANT CONSTRUCTIONS Comefrom： Createdate：2020/10/27 10:28:37 Hits：27
The reason analysis and solutions for insulaiton mortar cracks
Under the national building energy-saving and thermal insulation policy, it is now require external building wall to use external wall thermal insulation systems. The addition of external wall thermal insulation systems has improved the cold-preventing effect of cold area houses and is more energy-saving and environmentally friendly. However, during the construction of external wall insulation materials, improper operation easy cause cracks. What are the reasons for the cracks in external wall insulation materials and how should we solve it?
The external wall insulation system is to fix the insulation material and the building wall together to achieve heat insulation or heat preservation. Commonly used external wall thermal insulation materials include EPS thermal insulation board and external wall thermal insulation mortar, the cracks on the external wall easy happened on the various plaster bases such as cement mortar, various mixed mortars. Now we explain the reasons of cracks in the insulation material.
1. Crack reasons in EPS insulation board:
Stress differences, material shrinkage stress and freeze-thaw damage caused by temperature changes, unreasonable design and structure, unqualified materials and construction quality are major cracks reason in EPS insulation boards, furthremore, mechanical damage caused by wind pressure or earthquakes are also the crack reason . Because the EPS board thin plaster exterior wall insulation system is produced by a composite of multiple materials, the materials feature varies greatly. Polystyrene board as the main material for thermal insulation which has low thermal conductivity (0.038～0.041W/m•k) and is sensitive to temperature; thermal conductivity of polymer mortar is 0.93W/m•k, the thermal conductivity of the two materials difference is 22 times. When the external conditions change, the polystyrene board has a larger amount of deformation, which will cause interface tensile stress at the interface between the plastering mortar and the polystyrene board due to inconsistent material properties. Cracks will appear under one of the following conditions: First, the tensile stress (destructive force) generated by the change of the external environment is greater than the tensile strength of the anti-cracking wipe surface layer itself; second, the deformation of the wipe surface layer is greater than that under the influence of external conditions the amount of deformation of the insulation board. In order to prevent cracks, we must not only consider how to reduce the tensile stress that can cause damage, but also improve the tensile strength and deformation (flexibility) of the mortar layer (containing alkali-resistant glass fiber mesh) ).
2. Solutions for cracks in EPS insulation board:
We should find the root reason for EPS board thin plastered external wall external insulation system cracking in actual engineering applications, and specific measures should be combined with actual reasons to propose solutions.
Improve the bonding strength of the bonding mortar. Choose a suitable cement model; appropriately increase the amount of cement in the formula; increase the content of polymer powder in the formula; select a suitable thickening and water-retaining agent; increase the particle size of the sand and reduce the mud content.
Improve the quality of polystyrene board and ensure the curing period. Select qualified products to ensure that the bulk density of the polystyrene board meets the specification requirements; control the curing time before the polystyrene board leaves the factory.
Use qualified glass fiber mesh cloth. The bulk density is not less than 160g/m2; the glass fiber mesh cloth woven with alkali-resistant glass fiber filaments is preferred; the surface plasticity is not less than 20%; the mesh size is controlled at 4-5mm*4-5mm.
The performance of the plastering mortar should improve its flexibility, cohesive strength and construction operability. Choose a polymer redispersible latex powder product with a lower Tg value; keep the amount of polymer no less than 3% in the formula, to enhance cohesive strength and flexibility; choose high-quality quartz sand or washed river sand to reduce The influence of mud content on the performance of mortar; choose high-quality cement; use a variety of anti-cracking fibers and water-retaining agents to enhance operability.
Improve the flexibility of flexible putty. Choose a polymer redispersible latex powder product with a lower Tg value; increase the amount of emulsion; suggest to choose a two-component product with better cost performance; control the amount of cement in the formulation not to exceed 30%; a variety of anti-cracking fiber combinations use.
Avoid using low-grade paints, and use solvent-based paints with caution. The PVC of latex paint is not higher than 45%; use embossed texture technology as much as possible;
Good quality coatings such as elastic coatings and silicone resin coatings are preferred; solvent-based coatings should be used with caution.
3. Crack reasons in external wall insulation mortar:
Ordinary cement mortar itself has various shrinkage and deformation, there is a contradiction between strength growth fast and volume shrinkage slow. Under constrained conditions, when the tensile stress formed by volume shrinkage exceeds the tensile strength of cement mortar, it will be crack. The main structure has small deformation under the protection of the insulation layer because of less affected by temperature changes, while the 20~30mm leveling mortar is on the outer side of the polystyrene board with high thermal resistance, which will be greatly deformed due to the influence of environmental temperature. The cement material on both sides of the polystyrene board is affected by the environmental temperature difference and produces a relatively large difference in relative deformation, causing cracking. In addition, since the flatness of the thermal insulation board is difficult to control, it will cause unevenness in the thickness of the leveling plaster, causing local shrinkage and uneven temperature stress, which will cause cracks.
Cracks caused by incomplete external insulation. In external wall insulation, we often pay attention to the overall wall insulation, but ignore the insulation of parapets, awnings, dormer windows, bay windows, and external balconies. The density difference too big in the materials joiting posiotn of the insulation layer and other materials , this determines the elastic modulus and linear expansion coefficient between the materials are also different, the deformation under the temperature stress is also different, it is extremely easy to produce cracks in the surface layer in these parts. At the same time, waterproof treatment should be considered to prevent moisture intrusion into the insulation system and avoid damage to the system due to frost swelling, which affects the normal service life and durability of the system.
Unreasonable reinforcement causes cracks. The position of the steel rib mesh frame in the cement mortar is a single-side reinforcement, and it is close to the thermal insulation layer. The effects of positive and negative wind pressure, thermal expansion and contraction, dry shrinkage and wet expansion are all two-way or multi-directional. This kind of reinforcement has a limited effect on the stress dispersion near the exterior wall decoration layer, it has no good anti-cracking effect. The square steel mesh reinforcement has a good effect on resisting and dispersing the stress in the same direction as the steel mesh wire, but there is no reinforcement in the diagonal direction of the mesh, so it has limited use in resisting and dispersing the stress in the diagonal direction of the mesh. Therefore, it is easy to produce cracks along the diagonal direction of the four-corner mesh. In addition, the cement mortar at the cross of the four-corner steel mesh is not easy to be fully and fully gripped, so that the cement mortar and the steel mesh cannot become a common force.
4. Precautions and suggestions for external wall insulation construction:
Before construction, the condition of the base must be checked, especially the old building renovation and energy-saving renovation project, to avoid virtual adhesion between the cemented mortar and the base.
Strictly construct the polystyrene board in accordance with the specifications, the bonding area is not less than 40%, and it is forbidden to use only the point bonding method to ensure that the polystyrene board is firmly bonded; the polystyrene board seams are aligned and squeezed to avoid the height difference exceeding 2mm.
Strictly control the construction of nodes in accordance with standards, especially the windows.
At the junction of different materials, the polymer mortar and grid cloth of the surface layer should be extended 15-20cm with the non-insulation base layer to avoid cracks.
Be sure to check whether the surface of the polystyrene board is chalky before the construction of the plastering mortar. The thickness of the plastering mortar should be controlled at about 3mm; the position of the mesh cloth should be at the outer 1/3 of the plastering layer to avoid being close to the inner; Water calendering treatment.
The construction thickness of the flexible putty should be controlled within 2mm, preferably 1～1.5mm.
Training of construction team and improve the quality of workers.
Henan Ant Construction specializes in the production of external wall insulation mortar equipment, putty powder mix plant, dry mortar mixer machine. We committed to the research and development of energy-saving insulation equipment for urban buildings. It has newly developed new insulation material vitrified microbead perlite mixers and inorganic insulation mortar mix plant solutions to solve the problem of easy breakage of vitrified perlite during the mixing process, interested customers are welcome to consult at any time.
