In architectural decoration engineering, hollowing of plastering mortar is a common quality defect, manifested as a hollow layer between the mortar layer and the base layer, which will make a hollow sound when lightly tapped with a hard object. This problem not only affects the appearance of the wall, but may also lead to safety hazards such as tile peeling and paint cracking. To thoroughly solve the problem of hollowing, a systematic analysis needs to be conducted from three dimensions: materials, processes, and maintenance.
Grassroots treatment is the primary step in preventing hollowing out. If there is residual release agent or oil stains on the concrete wall, it will form an isolation layer, which will prevent the mortar from effectively bonding. A certain construction site once caused extensive hollowing due to the use of oil type release agents in the template, which ultimately required complete removal and rework. The correct approach is to use water-based release agents and chisel the base layer before plastering to form concave and convex points on more than 70% of the area, or use the slurry throwing method to form a cement nail like structure on the wall surface. For porous materials such as aerated concrete blocks, special interface agents need to be sprayed to avoid rapid absorption of mortar moisture by the base layer.
The material ratio and construction process directly determine the performance of mortar. A residential project experienced a 30% decrease in mortar bonding strength due to excessive sand and mud content, resulting in systematic hollowing. The specification requires that the mud content of sand should not exceed 5% and it should be filtered through a 3mm sieve. The amount of cement also needs to be precisely controlled. In a certain office building project, blindly increasing the proportion of cement resulted in an increase in mortar shrinkage rate, forming circular cracks in window sills and other areas. The correct approach is to select the strength grade of mortar based on the characteristics of the substrate. For example, M5.0 low strength mortar should be used for aerated concrete walls.
There are three major risk points in the construction process: firstly, the single plastering is too thick, and the standard requires the thickness of each layer to be controlled within 7-10mm. However, in a commercial complex, due to rushing the construction period, the single plastering reaches 15mm, resulting in the self weight of the mortar sagging and forming cavities; Secondly, there is insufficient interval between processes, and the next process is carried out before the initial setting of the previous layer of mortar, resulting in poor interlayer bonding; Thirdly, there is a lack of maintenance. After plastering, a certain hospital project did not do moisturizing treatment, and the mortar lost water too quickly in dry weather, resulting in a hollowing rate of 25% within 7 days.
Differentiated repair plans should be adopted based on the severity of the hollowing that has occurred. For point like hollow drums with a diameter less than 10cm, injection method can be used for treatment: drill a Φ 6mm grouting hole in the center of the hollow drum, use low viscosity epoxy resin for pressure grouting, and repair the hole after the resin solidifies. A certain hotel project adopts this technology, which can be restored to use within 24 hours. For sheet shaped hollows with an area exceeding 0.5 square meters, partial renovation is required: cut regular rectangles along the edge of the hollows, deep to a solid base, remove loose mortar, apply interface agent, repair in layers, and hang steel wire mesh for reinforcement.
To prevent hollowing, a full process control system needs to be established. In the material acceptance process, in addition to checking the certificate of conformity, on-site retesting should also be conducted, with a focus on testing indicators such as mortar water retention rate and setting time. Implement the "three inspection system" during the construction process: self check the flatness after base treatment, conduct a special inspection of moisture before plastering, and conduct mutual inspection of hollowing after plastering. A certain affordable housing project has reduced the hollowing rate from the industry average of 8% to 1.5% by setting up dedicated quality inspectors.
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