Cracks in Prefabricated Slabs Inside Buildings

Cracks in prefabricated slabs inside buildings require the identification of their causes based on their type, width, and accompanying phenomena, and the implementation of targeted measures. In severe cases, immediate inspection or reconstruction is necessary.

Common Causes

The occurrence of cracks in prefabricated slabs is primarily related to material properties and structural defects. Normal shrinkage cracks caused by the thermal expansion and contraction of concrete are one of the common causes. These cracks typically have a width ranging from 0.05 mm to 0.2 mm, appear only on the surface plaster layer, and stabilize after cracking, posing no significant threat to structural safety. Additionally, prefabricated slab houses use factory-made slabs that are assembled on-site, lacking overall solidity. Over time, issues such as wall water seepage and steel bar corrosion may lead to cracks. For example, water seepage causing steel bar corrosion leads to volume expansion, which squeezes the concrete and creates cracks; if the cement at the joints is not properly filled, uneven stress can also cause crack propagation.

Warning Signs

If cracks exhibit the following characteristics, structural risks should be a concern:

• Width exceeding 0.3 mm: This may involve construction defects or material aging;
• Abnormal shapes: Such as diagonal or spiderweb-like cracks, or cracks that penetrate the thickness of the slab;
• Accompanying phenomena: Wall peeling, building leaning, water leakage, etc., which may be caused by foundation settlement or insufficient slab load-bearing capacity.
  In such cases, immediate contact with a professional agency for structural inspection is necessary to avoid safety hazards.

Treatment Methods

Different measures should be taken according to the severity of the cracks:

• Normal cracks (≤0.3 mm): If they do not expand or show abnormalities, they can be left untreated temporarily and observed regularly.
• Cracks requiring repair: Chisel the cracks into a V-shape, remove loose particles, and then repair them with a specialized filler (such as epoxy resin) to avoid secondary cracking caused by direct patching with cement.
• Severe cases: If old houses have through cracks or cracks accompanied by structural deformation, demolition and reconstruction may be necessary to ensure safety.

Prevention and Precautions

Prefabricated slab houses have low structural strength and poor earthquake resistance. During renovation, avoid overloading (such as stacking heavy objects or removing load-bearing walls) to prevent increasing the risk of cracks. In daily use, regularly inspect the condition of the slabs and walls, and promptly repair water seepage issues to slow down the process of steel bar corrosion.