Preventing hollowing and cracking of premixed mortar(Ⅰ)

3.The strength of mortar cannot be too high

The strength of mortar mainly comes from the cement material. If the cement content is too high according to the strength grade, it will hydrate too quickly. And the cement hydration will produce hydration heat, which will increase the solid phase volume. But the absolute volume of the cement-water system is reduced. The initial water demand is large and the early strength is high. If the water sprinkling and curing are not timely, it will cause shrinkage and hollowing and cracking.

4.The mortar mix ratio is unreasonable

The total cementitious material or cement plus admixture of the mortar cannot exceed 400 kg per cubic meter. Because there is too much powder, the water retention is good, the surface is seriously delayed, and the mortar shrinks relatively large, which is easy to cause hollowing and cracking. The reasonable mix ratio is generally controlled between 280-340 kg per cubic meter of mortar cementitious material, and the sand rate is controlled at 80% ± 5. (The fineness modulus of sand is controlled at 2.4-2.7, and the mud content is within 3%). According to the relevant national or industry standards, the reasonable mix ratio can reduce the shrinkage of mortar from the source, reduce the shrinkage rate, and prevent shrinkage hollowing and cracking.

5.External wall grid

The main reason for cracks is that the wall is not grid-shaped. The shrinkage rate of cement is generally around 3‰. If the wall is not grid-shaped or the grid is too large, it is easy to shrink cracks. Therefore, the wall must be grid-shaped, and the smaller the style area, the better. When constructing the external wall, pay attention to the mortar that falls on the wire mesh must be cleaned up, otherwise it will greatly increase the chance of hollowing.
Preventing hollowing and cracking of premixed mortar(Ⅲ)