Common Causes And Solutions For Hollowing During The Use Of Terrazzo Prefabricated Panels

Common causes and solutions for hollowing in terrazzo prefabricated panels
Hollowing of terrazzo prefabricated panels refers to the phenomenon of hollowing between the panel body and the base layer (or bonding layer) due to weak bonding. The causes involve multiple aspects such as materials, construction, and environment, and the treatment needs to be targeted based on the reasons. The following is a detailed analysis:

1, Common reasons
1. Improper handling at the grassroots level
Surface pollution: The base layer (such as concrete floor slabs, leveling layers) is not cleaned thoroughly, resulting in residual floating ash, oil stains, release agents, etc., which leads to weak adhesion between the bonding layer and the base layer.
Uncontrolled water absorption: If the base layer is not pre wetted or has a high water absorption rate, the moisture in the bonding layer (cement mortar) is quickly absorbed by the base layer during paving. After the mortar loses water, its strength is insufficient and it cannot effectively bond the prefabricated board.
Poor flatness: The base layer is uneven, and the thickness of the bonding layer is uneven during paving - locally too thin (weak bonding force) or too thick (high shrinkage stress), which can easily cause hollowing.
2. Quality issues with the construction of the bonding layer
Improper material ratio: The water cement ratio of cement mortar is too high (with good fluidity but low strength), or the cement grade is too low, or the sand content is too high (>3%), resulting in insufficient strength of the bonding layer.
Uneven paving: The bonding layer is not evenly spread, and some areas are not compacted; Insufficient compaction during the laying of prefabricated panels (such as not evenly tapping with a rubber hammer) results in residual air inside and the formation of hollows.
Thickness out of control: If the bonding layer is too thin (<10mm), the bonding force is insufficient, and if it is too thick (>30mm), stress may occur due to shrinkage, leading to hollowing.
3. Problems with prefabricated panels themselves
Insufficient roughness on the back: The contact surface between the prefabricated board and the bonding layer has not been roughened, resulting in a smooth surface, small bonding area, and weak friction.
Size and strength defects: Prefabricated panels with excessive size (inconsistent deformation during thermal expansion and contraction) or insufficient strength (deformation under load) can damage the bonding layer.
4. Improper construction techniques
Incorrect laying sequence: such as laying from the middle to all sides without tightly pressing the edges; Or if the board is not fixed in a timely manner after laying (without temporary support), resulting in insufficient contact between the board and the bonding layer.
Lack of maintenance: Early dehydration of the bonding layer (such as uncovered maintenance in high temperature and strong wind environments), slow or reduced strength growth, and bonding failure.
Low temperature construction: During winter construction, the bonding layer is frozen, the cement cannot hydrate, and the strength cannot be formed.
5. Environmental factors
Extreme temperature: The construction temperature is too high (>35 ℃) or too low (<5 ℃), which affects the cement hydration reaction and leads to insufficient strength of the bonding layer.
Abnormal moisture content in the base layer: The wet base layer is not dry, and the evaporation of moisture in the bonding layer is hindered after paving, resulting in expansion stress and damaging the bond.

2, Handling measures
1. Preventive measures (pre construction control)
Grassroots treatment:
Clean up floating ash and oil stains on the base layer, moisten with clean water until there is no visible water; Smooth base needs to be roughened (such as using a chopping axe or mechanical roughening) to improve adhesion.
Repair the flatness of the base layer (measured with a 2m ruler, with an error of ≤ 3mm) to avoid uneven thickness of the bonding layer.
Combined layer control:
Use cement mortar with a strength of ≥ M15, with a water cement ratio controlled between 0.4-0.5 and a sand content of<3%; The thickness of the bonding layer is 10-20mm, and after paving, use a scraper to level it off.
Prefabricated board processing:
Check the roughness of the back surface, and if it is insufficient, use mechanical roughening or apply interface agent; Control the area of a single prefabricated panel (if necessary, set expansion joints with a spacing of ≤ 6m).
Environmental control:
The construction temperature should be between 5-35 ℃, avoiding rainy days, strong winds, and direct exposure to high temperatures; The concrete base layer needs to be cured for more than 28 days and laid after the moisture content is less than 10%.
2. Methods for handling empty drums
Small area hollowing (single board or partial):
Cutting: Use a marble machine to cut along the edge of the hollow drum, avoiding vibration and expanding the range.
Cleaning: Remove the hollow joint layer, clean the base layer and the back of the prefabricated board (without floating dust or oil stains).
Repainting: After the base layer is moistened, apply cement slurry (or interface agent), lay the bonding layer (cement mortar), compact and press the prefabricated board (evenly tapping with a rubber hammer), and cure for 7 days.
Large area hollowing (multiple boards or whole):
Demolition and re laying: If the hollow area is large, all prefabricated panels need to be removed, and the base layer and bonding layer need to be reprocessed before laying.
Grouting method (slight hollowing): Drill holes on the surface of prefabricated panels (spacing 300-500mm), inject low viscosity epoxy resin or cement-based grouting material, fill the hollowing gaps, and seal the holes after curing.
3. Strengthen maintenance and acceptance
Maintenance: Within 24 hours after laying, cover with wet burlap bags or plastic film to keep the surface moist, and maintain for at least 7 days.
Acceptance: Use a hollow drum hammer to lightly tap, with a hollow drum rate of ≤ 5% (excluding local hollow drums at the corners of a single board), otherwise rework is required.
3, Summary
The core of hollowing in terrazzo prefabricated panels is "bonding failure", which requires comprehensive prevention from five aspects: grassroots treatment, bonding layer control, prefabricated panel optimization, construction technology, and environmental management. When the drum is already empty, choose cutting and re laying or grouting repair according to the scope, and strictly inspect to ensure quality.