Cracking in Board Joints of Prefabricated Panel Houses

Whether to repair and how to repair the cracking in board joints of prefabricated panel houses should be judged based on the condition of the cracks, as follows:

If there are few cracks, the gaps are small, and there is no liquid flowing on the floor, no repair may be necessary. Such cracks are usually caused by concrete shrinkage or temperature changes and have a minor impact on the structural safety of the house, requiring no excessive intervention. However, it is necessary to regularly observe changes in the cracks. If signs of expansion or water seepage appear, timely treatment is required.

If the cracks are slightly larger and there is liquid leakage, immediate repair is necessary, with the following specific steps:

1. Chiseling the joint: Chisel open the cracked board joint, removing 5 centimeters from each side of the surface layer to create a sloped joint surface. At the same time, appropriately chisel the surface of the prefabricated floor slab and the side of the board to ensure a rough surface for enhanced bonding strength, and finally clean up the debris and dust.
2. Applying cement mortar: Apply a layer of pure cement mortar inside the board joint, with a water-cement ratio controlled between 0.4 and 0.5. This step seals the micro-pores on the surface of the crack, prevents mortar leakage during subsequent pouring, and provides a bonding base for the fine aggregate concrete.
3. Pouring fine aggregate concrete:
   • Pour for the first time to half the depth of the board joint to ensure that the concrete fully fills the underlying gaps;
   • After the fine aggregate concrete absorbs water for a moment (about 10 to 15 minutes), pour for the second time until it is compacted and leveled 1 centimeter from the floor surface. This operation prevents surface cracking due to concrete shrinkage and ensures alignment with the floor slab.
4. Curing and protection: After repair, cure for at least 2 to 3 days, during which stepping or stacking heavy objects is strictly prohibited. Curing can be achieved by covering with wet burlap or spraying water to retain moisture, promoting concrete strength growth and preventing new cracks due to drying shrinkage.

Precautions:

• When dealing with cracks, avoid drilling holes in the prefabricated panels to prevent damaging the internal reinforcement or prestressed structure of the floor slab and reducing its load-bearing capacity.
• If ceiling construction or other work needs to be carried out on the prefabricated panels, the hanging rods should be installed in the joints between two prefabricated panels, fixed to the concrete in the joint with expansion bolts to reduce damage to a single floor slab.
• Long-term leakage may lead to reinforcement corrosion. If the cracks are accompanied by rust stains or floor slab deformation, a professional institution should be commissioned to inspect the structural safety.