（1） Raw material issues: 1.
Low cement grade/insufficient amount.
Priority should be given to C25/C30 for the ground.
If low-grade cement is used or the cement content in the mortar layer is too low, the hydration strength will be insufficient, and the surface will become loose and powdery.
2.
The sand content exceeds the standard, and there are many impurities in yellow soil and silt, which wrap around cement particles and cannot form effective bonding.
After completion, it will start to dust as soon as it is rubbed; The standard requires sand to have a mud content of ≤ 3%.
3.
If the water cement ratio is too high (the most common), water can be added randomly during construction .
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