Views: 0 Author: Site Editor Publish Time: 2026-01-16 Origin: Site
Shijiazhuang Qingquan Cellulose Co., Ltd. is a Chinese manufacturer of HPMC/PVA/CMC/MHEC/HEC. HPMC is one of our key products, known for its excellent quality and reasonable price. It can be used as a thickener/water retention agent in mortar for construction. Qingquan Cellulose products are popular with customers worldwide.
Hollow areas and cracks in exterior wall plaster are common engineering quality problems. Their prevention requires systematic control across multiple stages, including substrate treatment, material control, construction techniques, and post-construction maintenance.
Common Causes of Hollow Areas and Cracks
Understanding the causes is the first step to effective prevention. The problems are usually caused by a combination of the following factors:
Improper substrate treatment: The wall surface is not properly cleaned before plastering, or is not adequately moistened, resulting in weak adhesion between the mortar and the substrate. Cracks occur at the junctions of different materials (such as concrete beams and columns and masonry walls) due to different shrinkage rates if anti-cracking measures are not taken.
Material and mix ratio problems: The strength of the plastering mortar is too high or higher than the strength of the wall substrate, or the mix ratio is unreasonable (e.g., too much powder, low sand content), leading to excessive mortar shrinkage.
Construction process defects: Plastering is applied too thickly in one go or not in layers, or the exterior wall does not have expansion joints or the joint spacing is too large, preventing the release of shrinkage stress.
Inadequate curing: After the plaster layer is completed, it is not watered and cured in time, or the curing time is too short (usually requiring at least 7 days), resulting in insufficient cement hydration and prone to shrinkage cracks.
Key Technical Points for Preventing Hollowing and Cracking in Exterior Wall Plastering
1. Substrate Treatment: Ensuring a strong and reliable bond
Cleaning and wetting: Before construction, the substrate surface must be thoroughly cleaned of dust, loose particles, dirt, and oil stains. The wall surface should be wetted before plastering, but ensure there is no standing water on the wall.
Interface treatment: Concrete substrates should be roughened or treated with a professional interface mortar. The use of unstable glue-cement slurry for roughening is prohibited.
Crack-resistant reinforcement measures: At the junction of different substrates (such as masonry and concrete beams and columns), crack-resistant steel mesh must be laid. The overlap width of the steel mesh with each substrate should not be less than 200mm. For highly absorbent walls such as hollow blocks and aerated concrete blocks, the leveling layer of plaster should be fully reinforced with steel mesh across the entire wall.
2. Material Control: Ensuring quality from the source
Mortar requirements: The raw materials, mix ratio, and strength grade of the plastering mortar must meet the design requirements and relevant standards such as the "Technical Specification for Plastering Mortar". The mortar strength should not be too high and should not exceed the strength of the base wall.
Mix ratio and performance: Control the total powder content of the mortar, ideally between 190-210 kg per ton, and use medium-coarse sand to reduce shrinkage. Crack-resistant fibers can be added to the mortar to improve crack resistance.
3. Construction Process: Precise operation of key steps
Layered plastering: Exterior wall plastering should be strictly carried out in layers. The thickness of each layer should be controlled between 5mm and 7mm. When the total plastering thickness is ≥35mm, additional reinforcement measures must be taken to enhance adhesion.
Setting expansion joints: When plastering large areas of exterior walls, expansion joints should be set to release shrinkage stress. The spacing of horizontal expansion joints should not exceed 6m, and vertical expansion joints should be set according to the wall area, not exceeding 30㎡.
Waterproofing at key nodes: Horizontal components of exterior walls such as canopies, air conditioning slabs, and protruding lines must have a drainage slope of not less than 1%, and the base should be made into a water-repellent arc corner, with a drip line at the lower edge. The exterior window sill should be sloped outwards (at least 10%) to prevent water accumulation.
4. Post-construction maintenance: Ensuring stable strength development
After the plastering is completed, watering and curing should begin after the mortar has fully set. The curing time should generally not be less than 7 days, and a dedicated person should be assigned to ensure that the plaster layer remains moist during the strength development period.
Quality Control and Responsibility Implementation
Clear Responsibilities: The construction unit bears primary responsibility, the design unit should clearly specify technical requirements in the drawings, the construction unit is fully responsible for construction quality, and the supervision unit needs to strengthen process inspection and on-site monitoring.
Strength Testing: Tensile bond strength testing of the exterior wall plastering layer should be conducted as required to ensure strong adhesion between layers.
Supervision and Inspection: The engineering quality supervision agency will include the quality of this exterior wall plastering layer in its routine inspections.
In summary, preventing hollowing and cracking of exterior wall plaster is a systematic project. By strictly adhering to the above technical points in the four key aspects of base treatment, materials, construction technology, and maintenance, the quality risks can be significantly reduced.
