Vertical Cracks in Prefabricated Floor Slabs of Houses

Vertical cracks in the prefabricated floor slabs of houses are usually structural characteristic issues caused by the splicing of prefabricated slabs. If not accompanied by structural damage, they generally do not affect the load-bearing safety and can be improved through decoration; if accompanied by deformation or wall cracks, professional identification is required.

I. Causes and Treatment of Common Vertical Cracks

Prefabricated floor slabs are composed of multiple prefabricated components spliced together. Vertical cracks are prone to occur at the joints in the middle due to concrete shrinkage or temperature changes. These cracks are usually parallel to the walls and are non-structural. Such cracks do not directly affect the load-bearing safety of the house but may affect aesthetics or cause local leakage. They can be treated with the following measures:

1. Mesh Application: For cracks at the top of walls, apply fiberglass mesh before scraping putty on the wall surface to cover the cracked area. The fiberglass mesh can enhance the bonding force between the base layer and the decorative layer, reducing the cracking of wall latex paint caused by crack expansion, but it cannot completely prevent the appearance of cracks.
2. Waterproofing Treatment: For floor cracks, first clean out the debris inside the cracks, fill them with waterproof coating or sealant, and then lay waterproof membranes or apply a waterproof layer. This can prevent moisture in cement mortar or self-leveling compounds from leaking through the cracks to the floor below, avoiding deformation of subsequent decoration (such as tiling or flooring) due to moisture.

II. Structural Safety Risks to Be Alert To

If vertical cracks are accompanied by the following situations, they may involve structural safety issues, and a professional organization should be immediately commissioned to conduct a house safety appraisal:

1. Floor Deformation: If there is obvious deflection (sagging) or bulging at the cracked area of the floor slab, it indicates that the overall stiffness of the prefabricated slab is insufficient, which may be caused by long-term overloading or concrete aging.
2. End Damage: If the cracks extend to the ends of the prefabricated slabs, resulting in loose or spalling concrete or exposed and rusted steel bars, it indicates that the connection at the joints has failed, and the impact of steel bar rusting on the load-bearing capacity needs to be evaluated.
3. Wall Cracks: If vertical or diagonal cracks appear in the load-bearing walls, especially if the crack width expands over time, it may be caused by uneven foundation settlement or overall structural instability. According to the "Standard for Appraisal of Dangerous Houses" (JGJ 125-2016), the house grade (A-D) should be determined, and then measures such as repair and reinforcement, reconstruction, or demolition should be taken.

Tip: Ordinary decoration treatment can only improve the apparent problems of cracks and cannot solve structural defects. If there are doubts about the nature of the cracks, it is recommended to contact a structural engineer or a house safety appraisal organization first to avoid secondary damage caused by blind reinforcement.