Why does the cement mortar plastered wall appear cracks?

 

Why does the cement mortar plastered wall appear cracks?

In the quality of construction engineering, wall cracks are a very common phenomenon. Mainly based on on-site experience, detailed observation and analysis of the on-site plastering process, starting with the quality of materials, national construction technology and industry specifications, etc., and detailed reasons for the cracks on the cement mortar plastered wall Based on the analysis, combined with their own practical experience, the corresponding solution strategy is proposed, and it is hoped that relevant engineering and technical personnel can use it for reference.

As people continue to improve the quality of building decoration, the quality of many existing decoration projects cannot meet the needs of residents, especially the formation of front cracks during cement mortar plastering operations. The wall cracks seriously affect the appearance of the building. At the same time, long-term cracks will be attacked by rain and cause damage to the overall structure of the building, affecting the stability of the concrete wall and posing a major safety threat to the structure of the building.
After the wall cracks occur, rework and repair operations are necessary, which greatly wastes manpower, material resources and financial resources and affects the service life and functions of the building. Therefore, in order to improve the engineering quality of the building wall to prevent cracks in the plastered wall, it is necessary to take measures to prevent and research. This article analyzes the reasons for the cracks in the cement mortar plastered wall and then combines its own engineering practice. The preventive measures have been elaborated in depth, hoping to provide reference and reference to relevant engineering and technical personnel.
Causes of cracks

Material quality issues:
1. Use unqualified materials
Cement is the main raw material for cement mortar plastering. Due to the rapid development of the construction industry in China, the cement market is in short supply. Therefore, after the cement sales season has passed, many cement manufacturers begin to make a large amount of production reserves for the second year of cement sales. The storage time in the warehouse takes more than half a year, which reduces the strength of the cement material and easily leads to unqualified quality. If the cement material cannot undergo in-depth inspection before entering the construction site, it is easy to cause unqualified quality, cause quality problems in cement mortar, and reduce the strength of cement mortar, which is an important factor in causing cracks in plastered walls. Sometimes, in order to reduce the production cost, cement manufacturers mix other mixed materials in the cement, such as coal gangue and waste slag. After this material is added to cement, it will increase the water absorption of the overall material, and the water absorption of the mortar will also increase. This will cause cracks in the plastering layer of the wall when the wall is plastered. phenomenon.

2. The amount of sand in the cement is unqualified
If the diameter of the sand particles used in the cement mortar plastering is less than 3mm, or the cement mortar with excessive mud content is used, the pores of the cement material will be filled, making the corresponding connection between the cement mortar and the aggregate impossible. The reduction of the cohesive force of the aggregate in the material will cause cracks in the cement mortar surface.

3. Incorrect calculation of cement mortar mix ratio
During the construction process, the proportion of cement mortar needs to be configured according to the specifications. If the construction personnel cannot correctly operate according to the standard specifications, the amount of cement will be inaccurate; if the heat of hydration of the cement is relatively large, corresponding temperature stress will be generated, resulting in Search for cement mortar; if the strength of cement mortar is low, its cohesive force will decrease, which will cause cracks in the cement mortar surface.
The plastering process operation does not meet the specification requirements:

1. The thickness of the plaster does not meet the specification requirements
In the process of building the wall, the verticality and flatness of the wall must be strictly in accordance with the requirements of the specification. If these do not meet the requirements of the specification, the thickness of the plaster will be different. If the wall is displaced during the masonry Larger, and produce various gaps, it will make the plastering uneven and produce greater deviations. If the layered plastering technology is not used in the plastering, it will cause irregular cracks on the wall.

2. The basic treatment of the wall is not clean
The base layer of the wall is the interface where the plaster layer is in direct contact, so the cleanness of the base layer directly affects the overall construction quality of the plaster layer. If there are scaffolding holes or other ventilation holes in the foundation of the wall, if the holes are not carefully repaired, the water entering the wall from these holes will have a destructive effect on the mortar layer. If it goes on for a long time, it will cause cracks in the cement mortar near the hole. If there are oil stains or honeycomb pockmarks on the concrete wall, the surface of the base layer is not cleaned, which will reduce the adhesion between the base layer interface and the cement mortar. If the adhesive force is less than the gravity of the cement mortar, the cement mortar will fall off, and finally cause cracks on the entire mortar surface. After the construction of the concrete surface is completed, if timely maintenance is not carried out, a certain loose layer will be formed. If the constructor does not pay attention to this problem, it will cause the cement mortar layer to separate from the base of the wall, plus the water in the air The effect of steam caused cracks on the wall. For different decorative materials, if the metal grid is not laid or the material is not split, the temperature and water absorption of the decorative materials will be different, which will cause the cement mortar to crack. Before plastering the wall with cement mortar, if the base layer of the wall is not wetted, the cement mortar will lose water prematurely during the hydration process and reduce its adhesion. As a result, the wall plastering layer shrinks prematurely and causes wall cracks.

3 The details of the cement mortar plastering layer have not been implemented
Cement mortar plastering basically follows the same operating principles on the construction site. Why do you get different quality results? The main reason is to correctly recognize the importance of the process of plastering operations. Especially in some details, such as detailed control of the thickness of the cement mortar, try to plaster the shape at one time, do not do layered plastering, and do not draw lines on the base layer; in winter and summer, it needs to be based on changes in the site temperature. Take effective measures in time for cracks in the cement mortar plaster layer of the house.

4. The cement mortar mixing measures are not in place
The use of cement mortar requires the mixing of the mixture to be uniform. If the mixture is not uniform, the operation will cause the hydration reaction of the cement; it is easy to cause stress concentration in the plaster layer and cause extended cracks , Affect the performance of cement mortar.

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