At present, dry mortar is in a rapid development stage, the use of dry mortar can effectively reduce resource loss, improve the quality of the project, improve the urban environment. However, dry mortar also exists more quality problems, if not regulated, will make its advantages greatly reduced, and even play a counterproductive. Only in the raw materials, finished products, construction site and other aspects of quality control, can really play out the advantages and role of dry mortar.
First, cracks
1. Grass-roots uneven settlement cracks
Uneven settlement of the grassroots, mainly refers to the wall itself caused by the subsidence of the cracks.
2. temperature cracks
Temperature changes will cause thermal expansion and contraction of the material, when the temperature deformation under the constraints caused by temperature stress is large enough, the wall will produce temperature cracks.
3. Drying Shrinkage Cracks
Drying shrinkage cracks are referred to as drying shrinkage cracks, and masonry such as aerated concrete blocks, fly ash blocks and other masonry will produce large drying shrinkage deformation of the material as the water content decreases. After dry shrinkage, the material will still expand after being wetted, and after dewatering, the material will undergo dry shrinkage deformation again.
4. Plastic shrinkage cracks
The reason of plastic shrinkage is mainly due to the short time after mortar plastering, it is in plastic state when the moisture is reduced to produce contraction stress, once the contraction stress exceeds the mortar’s own bond strength, it will produce cracks on the surface of the structure. Plastic drying and shrinkage of plastered mortar surface is affected by time, temperature, relative humidity and water retention rate of plastered mortar itself.
In addition, the negligence of design, not according to the specification requirements of the compartmentalized strip, no targeted anti-cracking measures, substandard material quality, poor construction quality, violation of the design and construction procedures, masonry strength does not meet the design requirements, as well as the lack of experience is also an important cause of wall cracks.
Second, hollow drum
1. Basic wall surface is not treated
Wall surface adhering to the dust, residual mortar and pouring isolation agent is not cleaned up, smooth concrete surface is not painted interface agent or spray slurry bristling, plastering is not carried out in advance before sprinkling sufficiently wetting, etc., will cause hollow drum phenomenon.
2. Rush to plaster the wall after insufficient maintenance time
If the wall is not sufficiently deformed before plastering, the grass-roots level and the plaster layer contraction is not consistent, resulting in hollow drums.
3. Single layer of plaster is too thick
When the wall is not well leveled or has defects, the wall is not treated in advance, and the plastering is in a hurry to finish the job at one time, and the plastering layer is too thick, resulting in the shrinkage stress being greater than the mortar adhesion, which produces the hollow drum.
4. Improper use of plastering materials
Plastering mortar strength and grass-roots wall strength mismatch, shrinkage difference is too large, is another reason for hollow drum.
Third, the surface sand
Surface sand is mainly due to the proportion of cementitious materials used in mortar is small, sand fineness modulus is too low, mud content exceeds the standard, mortar strength is insufficient to lead to sand, mortar water retention rate is too low water loss is too fast, after construction maintenance is not in place or no maintenance caused by sand.
Fourth, powder skinning
Powder skin mainly due to the mortar water retention rate is not high, the stability of the components in the mortar is not good, the proportion of mixing materials used is too large, due to the rubbing and calendaring lead to part of the powder upward, gathered on the surface, so that the surface strength of the surface is low and the powder skin.
FAQs
1. What are the common types of cracks in dry mortar?
The common types of cracks in dry mortar are uneven settlement cracks, temperature cracks, drying shrinkage cracks and plastic shrinkage cracks.
2. What causes hollowing out of dry mortar?
The causes of hollowing of dry mortar include failure to treat the surface of the base wall, rushing to plaster the wall after insufficient maintenance time, plastering a single layer too thickly, and improper use of plastering materials.
3. How to improve the problem of sand loss on the surface of dry mortar?
The problem of sand loss on the surface of dry mortar can be improved by increasing the proportion of cementitious materials in the mortar, using sand with suitable fineness modulus and ensuring timely maintenance after construction.
4. How to control the thickness of dry mortar during construction?
During construction, it should be ensured that the thickness of each layer of plaster should not be greater than 10mm, and when the thickness of plaster is greater than 10mm, it should be divided into layers, and the next layer of plaster should be carried out after the previous layer of mortar has solidified and hardened.
5. What are the common types of admixtures for dry mortar?
Commonly used additives in dry mortar are cellulose ether, dispersible latex powder, starch ether, water reducer, air-entraining agent, defoamer, anti-cracking fiber and so on.