How to avoid cracks in exterior wall putty powder? The specific reasons and solutions are as follows:
1. Reasons for cracking of exterior wall putty
1. Cracks in the base layer . The base layer of the exterior wall putty finish is a cement mortar plastering layer, which will produce dry shrinkage and temperature difference shrinkage during the setting process. If the exterior wall plastering construction is performed improperly, it will easily cause hollowing and cracking. If you don’t pay attention to repairing the putty surface before constructing it and then proceed to the next process, after a period of exposure to the sun and wipers, the internal cracks will gradually develop outward, and the putty surface layer with a very thin paint film is difficult to withstand these internal cracks. stress, cracking will occur.
2. Cracking of the putty layer. Due to defects in the quality of the exterior wall putty used, poor crack resistance; or due to improper construction operations, the putty shrinks and cracks after being scraped onto the wall, thus affecting the putty surface.
3. Cracking of the putty surface layer. Some putties with quality problems are prone to shrinkage, cracks and other quality problems after being exposed to wind and sun soon after being applied to the wall due to poor crack resistance or improper construction.
2. Material selection in preventive measures for exterior wall putty cracking
1. Cement used for plastering the base layer. It is best not to use early-strength cement that sets too quickly to avoid cracks caused by the cement mortar setting and drying out too quickly. The sand should be qualified river sand, and the particle size should not be too fine. Medium sand is best.
2. Selection of exterior wall putty. There are currently many types of exterior wall putty products on the building materials market, all of which are labeled with excellent crack resistance. You must choose carefully and try to use special crack-resistant flexible putty products produced by brands or large manufacturers. After the project starts, you can select several products that meet the standards and make putty base samples. After several months or more observation, when the project is about to enter the exterior wall decoration construction, you can generally compare which product is resistant to cracking performance.
3. Selection of putty. Through detailed market research and comparison, especially after investigating the actual application situation of the project under construction, select several qualified products of different brands, make samples as early as possible, and make choices through observation and comparison. In addition, according to experience, it is best to use thick crack-resistant exterior wall putty, such as elastic rough paint, relief paint and other types of putty. Since its coating thickness is more than 5 times that of ordinary putty, it has been found through construction practice that it can effectively withstand the load. The putty finish is cracked due to cracks in the base layer, and of course its price is higher than that of ordinary flat coating products.
3. Construction technology in preventive measures for exterior wall putty cracking
1. Construction of exterior wall mortar surface layer
①Cement mortar used for exterior wall plastering The proportion of cement mortar should be selected appropriately. Generally, 1:2.5 mortar is suitable. Try not to use 1:1 or 1:2 cement mortar.
If the amount of cement is too large, the mortar will shrink greatly and cracks will easily occur. To facilitate construction, an appropriate amount of fly ash can be added, or glue (such as 107 glue, etc.) can be added to increase the consistency of the mortar, improve the bonding force between the plastering mortar and the wall, and prevent hollowing and cracking. In addition, by adding Dura fiber (0.7kg of Dura fiber per m3 of cement mortar) and an appropriate amount of glue into the cement mortar, it has been found in construction practice that the crack resistance, anti-penetration and wear resistance of the mortar surface can be effectively enhanced. , which can enhance ductility and crack resistance, and the added cost is not large.
② Strictly follow the external wall plastering operating procedures and construction techniques. Before plastering, dust, dirt, oil stains on the base surface and ear dust on the brick wall must be carefully removed. The wall must be watered the day before construction, and 24 hours after construction is completed, it must be watered and maintained. The number of daily waterings should be determined according to the climate conditions, at least twice a day, and the maintenance time should be no less than 7 days.
③ The joints between brick walls and concrete beams and columns are prone to cracks. The method of nailing steel mesh to ride on the joints should be used at the joints to enhance the crack resistance of the mortar and prevent the occurrence of cracks. For the smooth parts of the concrete beams and columns, use cement mixed with 107 glue to scrape it once to increase the bonding ability between the mortar and the smooth base layer and prevent the mortar from hollowing and cracking in this part.
④ If construction is carried out in a season with sufficient sunshine, the construction time should be arranged scientifically to avoid construction under sunlight exposure, or effective shading measures should be taken to ensure that the mortar surface is dry in the shade and prevent the plastering mortar layer from being damaged by sunlight exposure. Cracks caused by rapid drying and shrinkage. ⑤ The divisions of the cement mortar plastering surface layer should not be too large. Make full use of the division gratings to adjust the shrinkage of the cement mortar. According to experience, the appearance of cracks can be effectively reduced if the grid is within a range of 2m.
During construction, wooden strips with triangular or trapezoidal cross-sections are used to divide the cement mortar surface layer. Construction joints are not allowed in the same construction section. The dividing joints should be caulked with caulking paste. 2. Construction of exterior wall putty layer
① Construction of exterior wall putty layer should be started after the plastering layer reaches the curing period.
② Before scraping the putty, the plastering mortar layer should be inspected, and the areas with hollows and cracks should be repaired 2 to 3 days in advance. Remove dust and floating sand from the plastering surface and keep the plastering surface clean.
③Construct strictly in accordance with the requirements of construction specifications and product instructions to ensure that the putty layer and plaster layer are firmly bonded and do not crack. At the same time, avoid working under sunlight during construction and ensure that the putty layer is in a dry state.
④ After the polishing process of the putty layer is completed, timely maintenance should be carried out, and at the same time, the powder produced by polishing should be washed away with water to make the wall clean so that it can enter the construction of the putty surface layer.
3. Construction of the putty surface layer
① Before the construction of the putty surface layer, ensure that the putty layer is flat, solid, clean, and free of defects such as looseness, powdering, and peeling. Check If defects are found, they should be repaired promptly.
②According to the putty finishing construction specifications and putty product requirements, the putty surface coating construction can be carried out only when the moisture content of the putty base layer is below 8% to 10%. Drying the putty base layer during construction is the key to ensuring that the putty surface layer adheres firmly and does not crack. Therefore, it is strictly prohibited to force construction without waiting for the putty layer to dry in order to meet the construction deadline.
③The putty surface layer is painted in several layers using different materials according to different functions. The painting construction of the last layer must be carried out after the previous layer of paint film is dry. The intervals between each coat are at room temperature. The duration is 2 to 4 hours, and the construction environment temperature should be above 5oC. Before each coat of paint film is applied, the previous process must be carefully inspected to ensure that it is qualified before construction.
④According to the construction technology and product requirements, the pH value of the base layer is required to be below 10.
Therefore, during construction, an anti-alkali primer must be applied first. It has good anti-mildew, anti-bacteria, acid and alkali resistance, and strong penetration into the putty layer, which can fully ensure the sealing of the putty layer and the putty layer. The bond is strong.
⑤ The construction of the putty surface shall not be carried out in wind conditions above level 4, or in rainy days, foggy days, or in environments with a relative humidity of more than 85%, to prevent dust raised by strong winds from contaminating the putty paint surface and to ensure the construction Surface dryness. At the same time, we should also try to avoid construction in hot sun or high temperature weather.
IV. Summary of exterior wall putty construction
In order to ensure that the exterior wall putty finish does not crack, the following should be done during construction: First, strictly control the materials and choose elastic and crack-resistant materials. , qualified putty products with good air permeability and strong adhesion. During the construction process, we strictly abide by the construction operating specifications and product process requirements, and control the construction quality of each process. Construction practice has proven that the common quality problem of cracking of exterior wall putty finishes can be completely avoided.