How to Handle Gaps in Prefabricated Houses

The treatment of gaps in prefabricated houses should be selected based on the type, size, and leakage situation of the gaps. The specific methods are as follows:

I. Small cracks without leakage

If the cracks are narrow, few in number, and there is no liquid flowing on the floor, temporary repair may not 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. However, regular observation is required to check for expansion.

II. Larger cracks with liquid leakage

Structural repair is required:

1. Chiseling the cracks: Chisel open the cracks on both sides of the slab, removing 5 cm of the surface layer on each side to make the joint surface slope-shaped. Chisel the surface of the prefabricated floor slab and the sides of the slab, and clean up the debris and dust.
2. Applying cement slurry: Brush a layer of pure cement mortar inside the cracks, with a water-cement ratio controlled between 0.4 and 0.5, to enhance adhesion.
3. Pouring fine aggregate concrete in layers:
   • Pour the first layer to half the depth of the cracks. After the fine aggregate concrete absorbs some water, pour the second layer.
   • Pour the second layer to 1 cm from the floor surface, compact and level it to avoid voids.
4. Curing: After repair, cure for at least 2-3 days. During this period, stepping on the repaired area is strictly prohibited to ensure the concrete reaches the required strength.

III. Gaps between prefabricated slabs

1. Repair with non-shrink epoxy structural adhesive:
   • Preferably use non-shrink epoxy structural adhesive during construction. If cracks have already occurred, use a wall planer to plane the surface plaster more than 10 cm and chisel out an inverted V-shaped notch.
   • After cleaning the dust with a blower, level the surface with the repair adhesive. Use an angle grinder to polish uneven areas.
   • Apply carbon fiber impregnating adhesive, paste carbon fiber cloth, and use an adhesive scraper to remove air bubbles to avoid voids. Finally, apply modified epoxy impregnating adhesive on the surface.
2. Inverted V-shaped notch removal method:
   • Remove the inverted V-shaped notch, plane it open 10 cm with a wall planer, and fill it with non-shrink epoxy repair adhesive.
   • After polishing it flat, apply modified epoxy resin adhesive and paste carbon fiber cloth to enhance tensile and bonding strength and prevent secondary cracking.

IV. Treatment of gaps between prefabricated floor slabs

1. Adjusting the gap width: During installation, control the gap difference (usually ≤ 30 mm) through reasonable slab arrangement to avoid excessive deviations.
2. Filling with fine aggregate concrete: When the gap difference is between 20 and 40 mm, use fine aggregate concrete with a strength grade of C20 or higher for filling. If necessary, add reinforcing bars or steel wire mesh.
3. Casting a concrete strip: When the gap difference is ≥ 50 mm, add a cast-in-place concrete strip with a width of not less than 200 mm at the gap. Configure longitudinal reinforcing bars inside to enhance integrity.
4. Adding reinforcing bars: For through cracks or areas with a large gap difference, add Φ6 to Φ8 reinforcing bars, arranged at the bottom or top of the gaps, to improve crack resistance.

V. Crack treatment during redecoration

During redecoration, flexible material reinforcement can be used:

1. First, fill the gaps with filling material.
2. Paste polyester cloth or mesh cloth on the outside to enhance crack resistance.
3. If the cracks are severe, further reinforce them by adding carbon fiber cloth.