In the construction industry, dry-mixed mortar is widely used in masonry, plastering, putty, tile adhesive and other applications, which solves the problem of mortar prepared by traditional processes. However, there always some problems in the use of dry-mixed mortar. What’s the problems and how to fix these problems?
1. Low bond strength
First, the workability of the mortar is too poor and low bond strength. Second, The construction personnel plastered too thickly at one time, and the plastering time interval was too short. Third, the substrate interface is not handled properly.
Solution: We can adjust the formula according to different raw materials and different substrates to increase the adhesion. Michem chemicals recommend layered plastering during construction, the total thickness should not exceed 20mm. We should pay attention to controlling the time of each process. For interface treatment, especially some new wall materials, special matching mortar should be used.
2. Peeling and powdering off
This problem occurs mainly because the fineness of the raw material sand used in the mortar is too small and the amount of admixture is too much. Due to excessive calendering during construction, part of the powder floats and aggregates the surface, so that the surface strength is too low and the powder falls off. Besides, the reason for the sand drop is that the mud content of the sand exceeds the standard and the proportion of cementitious materials is too small, which causes part of the sand to float out of the surface and form sand.
Solution: We should strictly control the sand fineness modulus, particle gradation, mud content and other indicators, increase the cementitious material, adjust the formula in time, adjust the material and addition ratio, and pay attention to the construction process and maintenance measures.
3. Rough surface
There are too many aggregates in the raw materials of ready-mixed mortar, such as large particles in sand, and the fineness modulus is too high, resulting in less slurry.
Solution: Adjust the particle gradation of the aggregate in the mortar and appropriately increase the amount of powder.
4. Hollowing, falling off, and infiltration
There will be some problems such as hollowing, falling off, and infiltration after the mortar is hardened. The production control management is not strict will lead to the mortar product quality problems, which will lead to problems in the quality of mortar products. Poor construction quality of construction companies and construction not strictly in accordance with the requirements of the specifications; It is caused by the mismatch between the interface agent, adhesion additive and dry mortar used in the interface treatment of the wall; temperature changes cause the expansion or contraction of building materials; the wall itself cracked.
Solution: Mortar manufacturers should improve the measures and responsibilities of mortar quality management. At the same time, construction enterprises should also improve the quality of mortar projects and provide professional knowledge training for production technology and construction personnel. For the choice of adhesion additive such as HPMC, we should choose a manufacturer with production experience and professional technicians. MilaCell™ is a trademark for Michem’s cellulose products and derivatives, providing cost-effective HPMC for use in mortar, good water retention and cohesiveness will delay the setting time of the mortar.
5. Plastic cracks
Plastic cracking refers to the cracking of the mortar before or during the hardening process. It generally occurs in the early stage of mortar hardening. The plastic cracking cracks are generally relatively thick and the crack length is short. It is mainly related to the material of the mortar and the temperature, humidity and wind speed. The higher the cement dosage, the smaller the sand fineness modulus, the higher the mud content, and the larger the water consumption, the easier plastic cracking of the mortar occurs. The higher the temperature, the lower the humidity, and the higher the wind speed, the more prone to plastic cracking of the mortar.
Solution: By adding water-retaining thickeners and admixtures in the mortar, reduce amount of cement , control sand fineness modulus and mud content, reduce water consumption. And control the environment during construction, try to avoid high temperature, dry and windy climate conditions, so as to reduce the risk of plastic cracking.
6. Dry shrinkage and cracking
Shrinkage cracking refers to the cracking of the mortar after hardening. It generally occurs in the late stage of mortar hardening. The shrinkage cracking is characterized by being thin and long. The main reasons for shrinkage cracking are that the amount of cement in the mortar is too large, and the strength is too high to cause volume shrinkage; the maintenance of the mortar in the later stage of construction is not in place; the admixture material incorporated in the mortar has a large drying shrinkage ; the wall cracks and improper handling of the interface; The grade of mortar is used indiscriminately or wrongly, and the difference between the elastic modulus of the substrate and the mortar is too large.
Solution: We can reduce the amount of cement, add suitable admixtures, and reduce the shrinkage value. Construction enterprises should strengthen the publicity and guidance of the technical knowledge of relevant personnel, make strict requirements from all aspects, and carry out construction in accordance with the construction method of dry-mixed mortar.
The mortar production enterprises do not use raw materials as required, the moisture content of the sand does not meet the sand drying requirements, the mortar mixing time is too short, and the mixing is uneven.The construction enterprise did not meet the requirements for rainproof and moisture-proof preparations during the storage process of the mortar, and failed to clean the dry mortar silos and mixers in time according to the construction requirements of ready-mixed mortar.
Solution: Mortar manufacturers should formulate a strict quality management system, strengthen production process control and raw material testing. Construction enterprises should strengthen the protection of dry mortar and improve the responsibility measures for the construction quality of mortar projects. The dry mortar silo should be assigned a special person to be responsible for maintenance and cleaning.
8. Unstable or non-condensing setting time
- The setting time of mortar is too short due to the high outside temperature, the high water absorption rate of the substrate and the low water retention of the mortar.
- The setting time of mortar is too long due to seasons, weather changes and excess admixtures.
- The mortar does not coagulate. Due to the unqualified cement quality or the uncontrolled measurement of the admixture, the mortar appears to be segregated with water, and the consistency is obviously too large and does not coagulate.
Solution: We can adjust the type and dosage of admixtures according to different seasons, different weather, and different wall materials. Strengthen the inspection of the construction site to understand the construction information in a timely manner; Strengthen the overhaul and maintenance of metering equipment to prevent equipment; Strengthen the sense of responsibility of operators and quality control personnel, and resolutely prevent substandard products.
On the one hand, it is caused by construction companies rushing to the construction period, which mostly occurs in winter and spring. On the other hand, composite products containing SO4, Cl2, or these are used as early strength agents.
Solution: Try to use low-alkali cement and admixtures, optimize the mix ratio, increase the density of cement-based materials; Avoid construction in dry, windy, low-temperature environments; And control the amount of water added during the mixing process of ready-mixed mortar; During construction, the floor material should not bleed, and the surface should not be in contact with water before it is completely dry., we can also use re-alkali inhibitor.
- Mortar admixtures or water-retaining thickening materials have poor compatibility with cement, resulting in the formation of bubbles in the reaction.
- The sand fineness modulus of the mortar raw material is too low or the particle gradation is not good, resulting in too high porosity and bubbles.
Solution: First,Strengthen the adaptability test of raw materials, especially admixtures and water-retaining thickening materials and cement, and use them for production after passing the test. Secondly, Reasonably adjust the particle gradation and various indicators of the sand to ensure the quality of the mortar is qualified.