Horizontal and Vertical Cracks in Prefabricated House Slabs

Cracks in the prefabricated slabs of a house, whether horizontal or vertical, require identification of their causes based on their direction and targeted treatment. Details are as follows:

Horizontal Cracks

Causes: Related to horizontal stress, often resulting from uneven foundation settlement, expansion and contraction due to temperature changes, or horizontal loads (such as wind or earthquakes).
Characteristics: Cracks run parallel to the house's transverse axis and may appear on the sides or bottoms of walls, floors, or beams, accompanied by floor sinking or wall tilting.
Treatment Recommendations:

• If there are few cracks, they are small, and there is no leakage, the impact on structural safety is minimal, and repairs can be temporarily postponed, but regular observation is necessary.
• If the cracks are slightly larger or leakage occurs, the slab joints should be chiseled open, and the base should be cleaned. First, apply pure cement mortar (water-cement ratio of 0.4–0.5), then pour fine aggregate concrete in two layers up to 1 cm from the slab surface, and finally cure for 2–3 days.

Vertical Cracks

Causes: Related to vertical stress, often caused by foundation settlement, material shrinkage, or compression due to the structural self-weight.
Characteristics: Cracks run perpendicular to the house's transverse axis and may extend from the top or bottom of walls or along the direction of reinforcement in columns.
Treatment Recommendations:

• If the vertical cracks are wide or numerous, they may affect the vertical load-bearing capacity of the structure and the usability of the house, requiring immediate assessment by a professional engineer.
• Avoid drilling holes in the prefabricated slabs during treatment to prevent damage to the load-bearing structure; if ceiling construction is required, install the hanging rods in the gaps between two prefabricated slabs.

General Recommendations

1. Professional Assessment: Cracks in different directions may reflect different structural issues and require identification of their causes and severity by a professional engineer through on-site inspection and calculation analysis.
2. Treatment Principles: Follow the process of "identifying the cause—comprehensive assessment—reasonable reinforcement—long-term monitoring" to ensure structural safety. For example, if the cracks are caused by foundation settlement, the foundation should be reinforced first; if caused by temperature changes, expansion joints can be added or insulation measures strengthened.
3. Long-term Monitoring: After treatment, regularly check for the expansion of existing cracks or the appearance of new ones, especially in earthquake-prone areas or houses with complex foundation conditions.

Tip: The treatment of cracks in prefabricated slabs should be carried out with caution, as non-professional operations may aggravate structural damage. It is recommended to prioritize contacting qualified inspection or reinforcement companies.