Mortar hollowing problem

1. Hollowing of mortar on shear walls often occurs on construction sites.

The fundamental reason why shear wall mortar is prone to hollowing is that the dry hard shrinkage rates of the concrete layer and the mortar layer are inconsistent, resulting in shrinkage stress. If the shrinkage stress is too concentrated at a certain point and is greater than the tensile bonding strength of the mortar and the wall at that point, hollowing will occur at that point and rapidly extend around the point, resulting in a large-area hollowing phenomenon.
The bonding force between the ready-mixed mortar itself and the smooth shear wall surface is far from enough, so an interface agent must be used. The function of the interface agent is to increase the bonding force between the mortar and the shear wall and increase the contact area between the mortar and the wall. This can evenly disperse the shrinkage stress between the mortar and the wall surface, effectively avoiding the large-area hollowing phenomenon caused by the shrinkage stress being too concentrated in one place.

2. At present, the most commonly used method on construction sites is to add construction glue and cement to roughen the interface.

However, there are still many quality accidents of mortar hollowing in quite a few projects. The reason is that this method of construction is very arbitrary. There is no exact formula for the ingredients, plus the quality of current construction glues varies widely. It is difficult to formulate an interface treatment agent with stable and good workability and bonding strength.
If more water is added, workers will feel easier during construction and the hair removal speed will be faster, but the hair removal will be too thin and flat, or even runny, and the rough interface effect of “hair removal” on the wall will not be achieved. If less water is added, workers will have difficulty in construction and the construction speed will be slow.
In order to increase the speed of pulling, some workers make the distance between pulls very wide. This kind of interface treatment method will cause the roughness to be thin and flat in most construction sites. If the spacing is too wide, there may even be some leakage on the wall. And the bonding force of the interface agent is obviously low.

3. The use of air compressors and spray guns for hair spraying is becoming more and more common.

And use type I concrete interface treatment agent produced by professional manufacturers (stretch bond strength is greater than 0.6MPa). It is a great improvement over the traditional “slapping” method and solves the problem of too wide spacing or missing hair.
Because its construction is relatively easy and labor-saving, it can be sprayed in place wherever it reaches. The spray points are uniform and rough, and the bonding force is strong, which can effectively disperse the shrinkage stress generated during the drying and hardening process of the mortar. Judging from the actual application on multiple construction sites, compared with the “hair-beating” method, the two methods have obvious differences in effectiveness in preventing shear wall mortar hollowing.