6.Requirements for interface agents

The requirements for interface agents are mainly reflected in two degrees.
The first is bonding strength (according to JC/T907-2002 “Concrete Interface Treatment Agent”, the tensile bonding strength is not less than 0.5Mpa);
The second is roughness (according to Appendix G of DBJ/T15-111-2016 “Technical Management Regulations for the Production and Application of Premixed Mortars”, the interface roughness determination method in the construction and quality acceptance of mechanical spraying interface mortar, the interface agent roughness should be 1.5mm).
At present, the most commonly used interface treatment method on construction sites is to use construction glue plus cement, or construction glue plus cement plus a small amount of sand to roughen the interface.
The traditional manual roughening is very arbitrary and there is no accurate formula for the ingredients. In addition, the quality of construction glue is different, so it is difficult to prepare a stable and good interface agent with bonding strength. At the same time, in order to facilitate construction and speed up the construction progress, the workers prepare the interface agent into a thin paste, and the roughening effect is thin and flat. It does not have the effect of a rough interface and falls off with a pinch.
An interface without bonding strength is prone to cause large-scale hollowing and cracking. This can cause quality accidents. It is recommended to use professional interface agent mechanical spraying to ensure the bonding strength and roughness of the interface and prevent hollowing and cracking of the plaster layer.

7.Maintenance of the plaster layer

The wall surface that has been plastered should be maintained in time, and a special person should be arranged to be responsible for watering and maintenance. The maintenance time cannot be too short, and the general maintenance period is 7 days. However, the construction site generally maintains for 1-3 days, which greatly increases the chance of cracking of the plaster layer.

8.Differences in construction environment

Premixed mortar will also have hollowing and cracking under different construction environments. Construction in a poorly ventilated and humid basement. Because the shear wall contains a lot of water, the water in the mortar is not easy to dissipate. And the initial setting time of the mortar is prolonged. As a result, the workers cannot finish the surface normally. It is often easy to cause the mortar to collapse or fall. Eventually cracks and hollowing occur.
To prevent such phenomena from happening, only adjustments can be made to the production mix ratio. Make the mortar have poor water retention and general viscosity. Reduce the dosage of admixtures. Water the construction wall 3-5 days in advance.

Conclusion

Hollowing and cracking of premixed mortar often occur. When you encounter hollowing and cracking of premixed mortar, you must carefully analyze the reasons. Find the real cause of its occurrence, make experience summary, prevention or prevention measures. Of course, if the construction of premixed mortar, wall selection, mix ratio, raw material selection, interface agent, maintenance and other aspects are standardized and perfected as much as possible. I believe that the occurrence of hollowing and cracking of premixed mortar can be eliminated.
Preventing hollowing and cracking of premixed mortar(Ⅰ)
Preventing hollowing and cracking of premixed mortar(Ⅱ)