Cracking on the Roof of Prefabricated Floor Slab Houses

Cracking on the roof of prefabricated floor slab houses is a common phenomenon in construction projects, especially prevalent in older houses, and requires targeted treatment measures based on specific causes.

Analysis of Cracking Causes

1. Concrete Shrinkage and Temperature Changes
   During the hardening process, concrete generates shrinkage stress due to water evaporation. If there is insufficient restraint between prefabricated slabs or improper curing, cracks can easily form. Temperature variations cause materials to expand and contract, and long-term cyclic effects may lead to structural cracking, particularly noticeable in regions with significant day-night temperature differences.

2. Construction and Design Defects
   When installing prefabricated slabs in older houses, if the gaps between slabs are excessively large (up to 4 centimeters in some cases) or the slab surface flatness is inadequate, stress concentration at the joints can occur, resulting in through-cracks. Additionally, failure to fully consider load distribution during the design phase or not setting temperature expansion joints can also increase the risk of cracking.

3. Material Quality Issues
   Insufficient concrete strength, improper reinforcement configuration, or the use of inferior sand and gravel during the production of prefabricated slabs can reduce structural durability and accelerate crack development. If aging materials are not replaced during the renovation of old houses, the problem may further deteriorate.

4. Improper Base Layer Treatment
   During renovation, if the top surface is not thoroughly cleaned of floating dust and oil stains, or uneven areas are not leveled, the new layer may not adhere firmly to the base layer, leading to hollowing or even detachment hazards.

Treatment and Prevention Measures

1. Crack Repair
   For minor cracks, pressure grouting with materials such as epoxy resin can be used to enhance the overall structural integrity. For through-cracks, the crack surface should first be cleaned, then reinforced with carbon fiber cloth or glass fiber mesh, and finally leveled with plaster.

2. Base Layer Strengthening Treatment
   Before renovation, the original loose top layer should be completely removed, and the surface should be leveled with cement mortar to an error of ≤3mm/2m. An interface agent should be applied to enhance adhesion. For joints with significant height differences, steel plate mesh or alkali-resistant fiberglass mesh can be added for anti-cracking treatment.

3. Budget Allocation for Renovation
   During the renovation of old houses, special funds should be allocated for roof treatment. Priority should be given to selecting lightweight, high-strength, and crack-resistant new materials, such as gypsum-based composite boards or calcium silicate boards, to reduce structural loads and lower the risk of cracking.

4. Long-Term Maintenance Recommendations
   Regularly inspect the roof condition and avoid concentrating heavy objects. Pay attention to insulation in winter and enhance ventilation in summer to reduce the accumulation of temperature stress. For repaired areas, it is recommended to conduct a professional assessment every 5 years to ensure structural safety.