Analysis of the Correlation between Common Surface Defects During Construction and Power Trowel Operation

The occurrence of surface defects in concrete is often not caused by a single factor, but rather the result of the combined effects of materials, the environment, construction techniques and equipment operation. As the final key process in floor forming, the operation mode of the power trowel machine directly affects the final quality of the surface.

The following is a detailed analysis of the causes of common surface defects, with a focus on elaborating their correlation with the operation of the power trowel machine.

Core correlation logic

The function of the power trowel machine is to compact, lift the slurry and smooth the surface of the concrete through the high-speed rotating power trowel. Improper operation can directly lead to or exacerbate the following problems:
Disrupt the uniformity of concrete (such as bleeding and segregation).
Change the water-cement ratio on the surface layer (such as by sprinkling water and grinding).
Introduce inappropriate stress (premature heavy-load operation leads to cracking).
It is impossible to effectively make up for the deficiencies of the previous processes.

Analysis of the Correlation between Common Surface Defects and the Operation of Polishing Machines

1. The surface shows signs of sanding and powdering

Defect description: Insufficient surface strength, loose cement and fine sand shedding.
The fundamental cause

The water-cement ratio on the surface is too high (bleeding or excessive watering).
The cement grade is insufficient or the quality is poor.
Improper maintenance causes the surface to lose water too quickly.
The correlation with the operation of the power trowel machine (main reason) :

Premature operation: Start smoothing the concrete when there is still a large amount of bleeding, removing the cement slurry and leaving only the sand.
Excessive water sprinkling on flour grinding: This is the most fatal operation. When the surface is dry, workers sprinkle water to save effort, which greatly increases the water-cement ratio of the surface layer and seriously reduces the surface strength.
The timing of power trowel is too late: The concrete has already begun to set, and the power trowel cannot effectively lift and compact the slurry. It merely "scraped" once and failed to bring the cement slurry to the surface.
Improper blade Angle or severe wear: Unable to effectively compact the surface layer.

2. Surface cracking/plastic shrinkage cracks

Defect description: Irregular, shallow and fine reticular cracks appear on the surface.
The fundamental cause

The evaporation rate of surface moisture is greater than the bleeding rate (in high-temperature, windy, and low-humidity environments).
Concrete itself has poor bleeding.
Correlation with the operation of the power trowel machine:

Failure to seal the surface in time: The first (bottom grinding) process of the power trowel is of vital importance. That is, under the aforementioned environmental conditions, when the concrete can reach the person mentioned above (about 25-30mm deep footprint), the power trowel should be used in conjunction with the disc to lift the slurry and seal it in time to prevent the water from evaporating too quickly. If the waiting time is too long and the crack has already formed, it will be of no avail to smooth it out.
Improper operation aggravates water loss: The high-speed rotating power trowel generates heat by rubbing against the concrete and accelerates water evaporation under the influence of air flow. In harsh environments, attention should be paid to operational efficiency. After completing a certain area, timely maintenance should be carried out.

3. Uneven surface/Poor waviness

Defect description: The ground is overall uneven, with a "ladle" or "wavy" feeling.
The fundamental cause

The initial flatness control of the laser screed is not good.
The slump of the concrete is uneven.
The correlation with the operation of the power trowel machine (main reason) :

The operation method is not professional

Without adopting the "horizontal and vertical cross" method: Always grinding in the same direction, it is easy to form a "furrow" effect, resulting in strip-shaped protrusions.
If the machine body stays in one position for too long, the weight of the power trowel and vibration will cause that area to slightly sink, forming a "dent".
Improper timing of raising or lowering the arm: When changing direction, failing to lift or lower the power trowel plate/power trowel smoothly can result in knife marks or local protrusions.
Uneven walking speed: The inconsistent speed leads to different degrees of compaction, resulting in color differences and slight height differences.

4. Surface color difference

Defect description: The ground color varies in depth.
The fundamental cause

The raw materials (especially cement) vary from batch to batch.
The pouring interval is too long, resulting in cold joints.
Correlation with the operation of the power trowel machine:

The timing of the finishing is not accurately grasped: There are slight differences in the initial setting time of concrete in different areas. If the operator stops the light in some areas when it is still bleeding (the color is bright), while in others when it is close to final setting (the color is dark), a color difference will occur.
Repeatedly grinding the same area: Repeatedly grinding a relatively wet local area will result in excessive slurry in that area and a color that is different from other areas.
Uneven watering: If water is sprinkled locally to grind the surface, it will directly cause the water-cement ratio in that area to be different, resulting in a lighter and whiter color.

5. Hollowing/peeling

Defect description: The surface-hardened layer has detached from the lower layer.
The fundamental cause

The surface is over-polished, forming a dense but fragile cement paste layer, which is inconsistent with the contraction of the lower layer.
The lower layer of concrete has severe bleeding, forming a water film and weakening the interlayer bonding force.
The correlation with the operation of the power trowel machine (key reason) :

Excessive finishing: Forcing the use of a power trowel machine after the concrete has r

The correct construction guide based on the operation of the power trowel machine

To avoid the above-mentioned defects, the operation of the power trowel machine should follow the principle of "timely and moderate".

Summary

An excellent power trowel operator is not only a machine operator but also an "observer" and "manager" of the concrete setting process. He needs to understand the fundamental principles of materials science, and through precise operation timing and proficient techniques, transform the solid foundation created by the laser screed into a high-quality floor with high strength, high flatness and no defects.

Note: The parameters provided in this document are for reference only and are not mandatory. Due to differences in technical characteristics between different brands and models of laser levelers, please consult the manufacturer for a suitable solution before actual operation. This reference document assumes no responsibility for any issues arising from failure to follow the manufacturer's instructions.

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