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1、 Summary of causes of hollowing and cracking of plastering
1. The oily release agent is used for formwork release, the concrete surface is too smooth and the adhesion is poor, resulting in hollowing and cracking of plastering surface.
2. The masonry construction is unreasonable, and the masonry settlement leads to hollowing / cracking of plastering surface.
3. At the junction of different materials, there is no net hanging treatment, or the method of net hanging is unreasonable, resulting in air crack.
4. The slotted surface of the multi pipe line is not sealed or the sealing method is unreasonable, resulting in the hollow crack of the plastering surface.
5. Before plastering, the concrete and autoclaved masonry are not grouted or have poor adhesion.
6. The plastering mortar is mixed randomly without effective guarantee of mortar strength.
7. The strength of mortar can be reduced by adding additives such as mortar king.
8. If the thickness of one-time plastering is too thick (more than 12mm) or the interval time of layered plastering process is not enough (less than 12h), the mortar on the plastering wall will slip, and the plastering layer is prone to appear sagging cracks in a horizontal direction, making the plastering layer on the wall empty;
9. The plastering finished surface is not cured in time, and there is no effective water conservation measures.
10. After plastering, the pipeline is slotted and installed, and the sealing method is unreasonable.
2、 Cause analysis and improvement of anti air bulge and crack in plastering
Cause analysis:
Oil or solvent type release agent is used on the surface of wood formwork, which causes too smooth plastering surface or residual oil residue on the surface, poor adhesion and hollow crack of plastering surface.
Improvement practices:
The water-based release agent shall be used for the release of non fair faced concrete to control the removal time, which can not only ensure the quality of concrete forming, but also ensure the concrete adhesion and reduce the risk of air crack in the later stage.
Cause analysis:
The inclined roof brick is not dense and the angle of the inclined roof is too large. The inclined roof of the long wall is built in the same direction, which is easy to crack in the later stage.
Improvement practices:
The inclined roof brick shall be densely built with an angle of 45-60 degrees. When the wall is long, the inverted splayed two-way masonry shall be used, and the finished triangle block shall be used in the middle part.
Cause analysis:
The joint of structural column and masonry is not provided with tenon, which reduces the seismic and crack resistance performance of structural column.
Improvement practices:
The tenon of structural column shall be retreated first and then moved in, and the partition shall be moved in and out. The length of tenon shall not be less than 6cm. The tie bar of structural column shall be retained every 50cm, and the length of tie bar entering the masonry shall be 500mm.
Cause analysis:
The short buttress wall beside the door is built by cement brick without biting, and the short buttress concrete has no planting reinforcement, so its crack resistance is poor.
Improvement practices:
In order to improve the stability of the short buttresses, the cast-in-place structure can be used instead of the short buttresses.
Cause analysis:
There is no net hanging treatment at the junction of different materials; the galvanized net is directly pasted with cement mortar and arched with galvanized net
And the crack resistance is insufficient.
Improvement practices:
The concrete and sintered brick are fixed with insulation nails to the galvanized mesh, and the sand aerating is fixed with cement nails. When fixed, the galvanized mesh is flat and does not arch.
Cause analysis:
The slotting of whitewash front line pipe is not blocked, the line pipe and masonry are not fixed, and the crack resistance is poor.
Improvement practices:
After the pipeline installation is completed, the fixing clamp or cement nail shall be used to fix the pipeline. Before plastering, the pipeline slot shall be sealed in time. The single and double line pipe slot can be sealed with crack resistant mortar. The third line pipe and above shall be sealed with fine aggregate concrete and micro expansion agent. After sealing, the galvanized steel wire mesh shall be used for reinforcement.
Cause analysis:
The slotting depth of the line pipe is insufficient, the line pipe is fixed beyond the masonry surface, and the plastering surface is a weak part, which is easy to cause cracking.
Improvement practices:
Strictly control the groove depth of the line pipe, DN + 10 mm ≤ groove depth ≤ DN + 20 mm, groove width DN + 20 mm ≤ groove width ≤ DN + 60 mm. Avoid too deep slotting to damage the wall and too small slotting to block
Difficult to compact.
Cause analysis:
The shotcreting fullness of concrete is not enough, the strength is poor, there are more shotcreting peeling, reduce the adhesion, easy to lead to plastering cracks.
Improvement practices:
The concrete shotcrete is insufficient in fullness, poor in strength, and there are many spalling of shotcrete, which can reduce the adhesion and lead to hollow crack of plastering.
Cause analysis:
The plastering mortar is mixed randomly without fixed feeding proportion, the sand content of mortar is too high and the mixing is uneven.
Improvement practices:
Make clear the mix proportion of plastering mortar, set up effective measurement facilities, strictly control the feeding ratio, set a group of mortar test blocks in each batch and send them to the third party unit for compression test, brush the large flour construction, and record the feeding ratio of mortar every two hours.
Cause analysis:
The use of mortar king and other national orders prohibit mortar additives, reduce the strength of cement mortar, which is easy to cause hollow cracks and sand on the plastering surface.
Improvement practices:
Strictly determine the mortar feeding and ratio according to the laboratory proportioning list, forbid the use of mortar king and other national orders forbid the use of mortar
Additive to ensure the strength of cement mortar.
Cause analysis:
After plastering for one time, the cement mortar flows down and cracks the plastering surface.
Improvement practices:
Strictly control the thickness of one-time plastering and plastering interval time. The thickness of single-layer plastering should be controlled within 1.2cm, and the plastering interval time should be more than 12 hours. Considering the effectiveness of management, it is recommended to paint the bottom coarse ash and the surface layer every other day.
Cause analysis:
Maintenance and water conservation measures shall be taken after plastering, and the plastering surface is likely to crack in hot and dry weather.
Improvement practices:
In hot and dry weather, the plastering surface shall be watered every four hours for curing, and the duration shall be controlled for one week, or the celite water retaining agent can be used, and the curing time can be set to once every two days.
Cause analysis:
After the plastering surface is slotted, the unreasonable sealing method is easy to produce hollowing and cracking.
Improvement practices:
Before plastering, the pipeline shall be completely installed to avoid cracks on the plastering surface caused by slotting behind the plastering surface; if it is necessary to slotting after plastering, the slotting depth and sealing process shall be strictly controlled.
The depth of slotting after plastering surface shall be controlled at a distance of more than 2cm from the pipeline to the plastering surface. Micro expansion agent shall be added to the plugging mortar, and the plugging shall be completed in two times with an interval of more than 12 hours.