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How to deepen / optimize the design of exterior wall thermal insulation coating project? The design process is here! Taobao platform announced
Glass bead thermal insulation mortar is one of the most widely used technologies in the thermal insulation system of building exterior wall, and the hollowing of thermal insulation surface is a common quality defect. Based on this, this paper analyzes the causes of hollowing of vitrified bead thermal insulation mortar, and puts forward some construction quality control measures. It has been proved that these measures are effective to avoid hollowing and promote the development and application of vitrified bead thermal insulation mortar.
Glass bead thermal insulation mortar has excellent weather stability, excellent thermal insulation, good fire performance, simple construction and high cost performance, its application is more and more popular. The glass bead thermal insulation mortar system is composed of interface layer, thermal insulation layer, anti crack mortar fiber net, anti crack mortar and facing layer. The hollowing in the project is one of the main engineering quality problems. The reason is not only related to the performance of thermal insulation mortar itself, but also related to construction technology, construction quality control and supporting materials.
1 project overview
The project is mainly composed of 10 29-33 storey residential buildings, covering an area of 68313m2, with a building area of about 289571m2. The earth excavation depth of the basement at different stages is 1.8-7m, and the underground building area is about 50476m2. The proposed buildings are all frame shear wall structures. Because there are many buildings and large quantities of works on site, it is very important to control the quality of external wall insulation. Figure 1 is an engineering building overlooking.
2. Causes of hollowing
2.1 material factors
First, the formulation of the material itself. The formulation of the material is not optimized according to the engineering conditions of the construction site, and the properties of the thermal insulation mortar such as water retention and tensile strength cannot meet the requirements of the project, resulting in hollowing. There is a problem in the quality of the material itself, which leads to the poor water retention effect of the mortar and the formation of hollowing. The solubility of the modified components such as cellulose and latex powder in the material did not take full account of the factors such as the construction temperature and the strong alkali of the gel material, and did not fully dissolve the function, so that the water holding capacity and the tensile strength could not meet the requirements, and the hollowing drum appeared. Figure 2 is an example of hollowing of thermal insulation mortar surface.
Second, the site mixing is not uniform, part of the vitrified micro bead mortar bonding force is insufficient, causing the insulation layer hollowing. In the absence of equipment on site, manual mixing is adopted, which will increase the amount of mixing water, resulting in high moisture content in some positions after the insulation mortar is put on the wall, and water flow will form hollowing.
Third, the mixing water is not clean, there are too many impurities, resulting in more bubble like hollows.
2.2 base wall
2.2.1 the surface of base course is loose. The concrete surface is crisp and not solid, which is equivalent to the formation of an isolation layer between the base wall and the mortar layer, that is, the formation of mortar hollowing.
2.2.2 the wall surface is not clean enough. The base wall surface is not well treated, with garbage, dust or pollutants. In addition, in the interface treatment before the construction of thermal insulation mortar, the release agent on the wall surface was not cleaned. After the thermal insulation mortar was plastered, the actual bonding was not tight, and some positions formed hollowing.
2.2.3 the wall is not well wetted before construction. The moisture in the mortar is absorbed by the base quickly, which causes the water loss of the mortar to be too fast, so the hydration effect of the cement particles in the mortar cannot be fully exerted, which affects the bonding with the base. If the base course is over watered, there will be a water film between the base course and the insulation layer, which will also affect the bonding with the base course. If the base course has different degree of dryness and wetness or uneven watering, it will cause uneven dryness and wetness on the wall and form hollowing and cracks.
2.2.4 the base course is too smooth and flat. If the interface treatment is not in place, the adhesion of the base course is low, which is easy to lead to hollowing, cracking and even falling off of the direct laying mortar layer.
2.3 base structure
First, uneven settlement. It is easy to cause hollowing or local falling off of thermal insulation mortar layer near the expansion joints of long and large buildings.
Second, the external wall decorative components are not fixed firmly, forming push-pull effect, resulting in partial hollowing of thermal insulation mortar layer.
Third, after the completion of the thermal insulation project, the artificial damage caused by the installation of doors and windows, air conditioning, downpipes and other decoration construction in the later stage will cause hollowing. The gaps between the building doors and windows or walls and the insulation system are not sealed with sealant, resulting in long-term water seepage and infiltration of the insulation mortar, causing hollowing.
2.4 construction factors
The external wall insulation structure is shown in Figure 3, and the specific construction factors are as follows. First, the thickness of single application is too thick, which will lead to large shrinkage deformation and affect the bonding ability of mortar. The bonding force of mortar is less than the internal stress of shrinkage, and it is also easy to produce hollowing.
Second, improper troweling before final setting of thermal insulation mortar. As the thermal insulation mortar is different from cement plastering, it has certain elasticity before final setting, and will rebound after the iron trowel is overpressured, which is easy to form hollowing. At the same time, the surface of the thermal insulation mortar is smooth, which is not conducive to bonding with the crack resistant reinforcement layer, and may also lead to hollowing.
Third, the construction of individual positions is not careful. For example, if the construction personnel are not careful, the vitrified bead thermal insulation mortar at these positions will not be applied in place, leaving gaps, etc., resulting in hollowing.
Fourth, the time of disturbing mortar is too early. The mortar will be disturbed before it is dry, which will easily lead to the falling of the upper part, the overall sagging and the formation of hollowing.
Fifthly, the degree of compaction after the mortar laying is not enough, which reduces the bonding area between the thermal insulation mortar layer and the base layer, resulting in the hollowing of the mortar layer.
3. Prevention and control measures for hollowing in the project
It is found that the process control, especially the material quality and construction technology control, should be paid attention to in order to prevent the hollowing of the vitrified bead thermal insulation mortar, so as to minimize the hollowing of the vitrified bead thermal insulation mortar.
3.1 material selection
First, the vitrified micro bead finished mortar dry materials shall be continuously supplied in batches after passing the re inspection of mobilization performance, and shall be selected to ensure the quality stability of thermal insulation mortar finished products. Ordinary portland cement with high early strength and low dry shrinkage during setting and hardening should be preferred for the cement of vitrified bead thermal insulation mortar. The vitrified micro bead thermal insulation mortar and its supporting materials shall optimize the material mix proportion according to the type and nature of the base wall on site, construction temperature and humidity, temperature of the thermal insulation layer and the thickness of single application, so as to make its working performance and strength meet the corresponding technical requirements. Figure 4 shows the selection of dry materials for vitrified bead thermal insulation mortar.
Second, the right choice of redispersible latex powder, in order to give insulation mortar reliable adhesion, long-lasting flexibility and good durability.
Third, in the production process of vitrified bead thermal insulation mortar dry powder, emulsion powder, hydroxypropylmethylcellulose, etc. are dissolved first, and then added after other mixtures are stirred evenly. In this way, the mortar is easier to mix evenly, and can reduce the damage of the mixing to the vitrified bead particles, so that the reaction of each component of the system is more sufficient.
Fourthly, the mixing time of the vitrified bead thermal insulation mortar should be strictly controlled. The mixed slurry should be used up before the initial setting to prevent the slurry bonding performance from declining. The slurry beyond the initial setting time should not be used.
3.2 base treatment
First, before the construction, the dust, dirt and residual mortar on the surface of the base course shall be removed, the loose and weathered part of the wall surface shall be chiseled, and the protuberances higher than 5mm on the wall surface shall be leveled. Broom or roller shall be used for the base course to brush the interface agent slurry evenly and completely. After the final setting, it must be watered and cured until the strength meets the requirements.
Second, the wall surface where the mortar layer is laid shall be watered two days in advance to avoid the phenomenon of laying while wetting or laying without wetting. If the base course is found to be too dry during painting, the base course shall be watered again, but not too wet. The wall shall be watered evenly to prevent excessive deviation of the degree of dryness and wetness. It should be noted that the wetting time and water quantity of different wall base are different.
Third, if the wall is smooth, it should be roughened first. That is, first clean the dust and dirt on the surface, and then roughen the base with cement mortar to increase the bonding strength between the thermal insulation mortar layer and the wall. After the cement mortar has proper strength, spray water slightly to wet, and properly dilute the consistency of the mortar, so as to achieve the purpose of laying mortar. After the final setting of thermal insulation mortar, spray water for maintenance to avoid dry shrinkage cracks after water loss of thermal insulation mortar layer.
3.3 construction process control
First, in view of the hollowing of the insulating layer caused by the uneven mixing at the construction site and the insufficient bonding force of some vitrified bead slurry, appropriate mechanical mixing shall be selected to appropriately extend the mixing time of the rubber powder. After the rubber powder is evenly mixed, the inorganic vitrified bead shall be added for short-term mixing.
Second, the construction thickness of single application shall be appropriate. The strength of thermal insulation mortar itself is relatively low, once the thickness is too large, it will fall due to the excessive self weight, and it is easy to cause debonding and hollowing. Therefore, after the application of interface agent, the thickness of thermal insulation mortar for the first time shall not be greater than 15mm, and it is not allowed to repeatedly knead and press under the semi setting state of mortar. After the insulation mortar is dry, do not carry out the construction operation of equal collection to prevent disturbing the bonding surface, as shown in Figure 5.
Third, the insulation mortar shall be constructed in layers according to the design thickness. The first plastering shall be uniformly compacted, and the next plastering shall be carried out after the previous plastering is hardened. The thickness of the last plastering shall reach the thickness of ash cake and screeding, and shall be rubbed with a large bar. Spray water for curing within 24 hours after the completion of insulation layer construction, and the curing time shall be ≥ 3 days. After the insulation layer meets the maintenance conditions, the anti crack mortar insulation layer can be constructed, as shown in Figure 6. The insulation layer shall be vertical, flat, square and straight, or it shall be repaired.
The hollowing of vitrified micro bead thermal insulation mortar surface layer has become an important disease affecting the quality of the project. Therefore, this paper starts from four aspects: material factor, base wall, base structure and construction factor, and puts forward prevention measures from three aspects: material selection, base treatment and construction process control, so as to reduce the hollowing phenomenon Improve the service life of the thermal insulation surface layer of the outer wall of the vitrified bead thermal insulation mortar.
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How to deepen / optimize the design of exterior wall thermal insulation coating project? The design process is here! Taobao platform announced
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