Cracks in Prefabricated House Slabs

When cracks appear in the prefabricated slabs of a house, it is necessary to determine their nature and degree of hazard based on their characteristics and take targeted treatment measures.

1. Determining the Nature of Cracks

1. Unidirectional Parallel Cracks: If the cracks are unidirectional and parallel to one side of the wall, they are usually caused by asynchronous deformation of two prefabricated slabs. In cases where there is no significant deflection (i.e., bending deformation) of the floor slab, such cracks generally pose no safety hazards but may lead to rainwater leakage through the gaps, requiring attention to waterproofing.
2. Crack Characteristics Requiring Vigilance: If the cracks continue to widen, the floor slab shows visible deflection or deformation, or the indoor cracks are continuous and wider than 0.7mm, they may affect structural safety and require immediate professional inspection, identification, and reinforcement.

2. Crack Treatment Measures

1. Cracks Without Safety Hazards:
   • Surface Treatment: Use methods such as applying mesh fabric, epoxy resin coating, or carbon fiber reinforcement to enhance the tensile resistance of the cracked area and prevent further crack propagation.
   • Waterproofing Treatment: If the cracks are located in damp areas such as bathrooms or kitchens, apply waterproof coatings after surface treatment to prevent leakage.
2. Cracks Requiring Professional Intervention:
   • Inspection and Identification: Commission a structural engineer or professional agency to assess the impact of the cracks on structural safety through methods such as load testing and ultrasonic testing.
   • Reinforcement Treatment: Based on the inspection results, use methods such as steel plate bonding reinforcement, external prestressed reinforcement, or adding support systems to restore the structural load-bearing capacity.

3. Possible Causes of Cracks (for Reference)

1. Design Factors: The structural design does not fully consider the impact of construction environment (such as temperature and humidity changes) on the deformation of prefabricated slabs, resulting in insufficient design for critical conditions.
2. Material Issues: Poor quality of concrete raw materials (such as insufficient cement grade, high mud content in aggregates), unreasonable mix design (such as excessive water-cement ratio), leading to insufficient concrete strength or excessive shrinkage.
3. Construction Issues: Inadequate curing (such as not covering for moisture retention, insufficient curing time) or premature loading (such as stacking heavy objects before the concrete reaches the design strength), causing shrinkage cracking; the support system does not match the plan (such as excessive support spacing) or premature removal of supports, leading to uneven stress on the prefabricated slabs.

Tip: Crack treatment should be comprehensively judged based on specific causes and degrees of hazard. Ordinary users can prioritize observing the trend of crack changes and contact professional agencies promptly if there are safety hazards.