Technical Knowledge
Requirements and treatment for troweling the concrete base layer before grinding special floors (such as epoxy floors and curing agent floors)
The success of special floors (such as epoxy floors and curing agent floors) is "70% dependent on the base layer and 30% on the materials". The quality and treatment of the base concrete's smoothing are the key prerequisites for determining the final floor effect and lifespan. The following are the detailed requirements and treatment procedures for the concrete base layer before grinding.
Core principle
The objective of the base concrete is to provide a "canvas" that is of high strength, dense and smooth, dry and clean, and free of defects.
Ⅰ. Requirements for Concrete Base Smoothing (Pouring Stage)
This refers to the operation carried out using a mechanical trowel during the period from the initial setting to the final setting of concrete. The requirements are far higher than those for ordinary concrete floors.
Concrete grade and proportion
The strength should not be lower than C25, and it is recommended to be above C30.
The water-cement ratio should be low (generally ≤0.5) to reduce bleeding, enhance surface strength and wear resistance.
The aggregate (sand and gravel) particle size is moderate and the mud content is low, ensuring a fine surface.
Pouring and vibration
It is necessary to vibrate thoroughly to expel air bubbles and ensure that the concrete is dense, free of voids and honeycombs.
Key step: Polishing process
Preliminary leveling: After the concrete is laid, a laser screed or a scraper is used for initial leveling.
Bleeding treatment: Allow the free water on the surface to fully evaporate. Start the operation before the initial setting (when the depth of the human footprint is about 2-3mm).
The first coat of troweling (lifting the slurry) : Use a circular troweling machine to run at low speed to lift and smooth the surface slurry, filling in local unevenness.
The second coat of smoothing (compaction) : When the surface moisture has further evaporated (and the footprints left by a person standing on it are very shallow), switch to a trowel blade (iron plate), run at medium speed, and apply in a cross direction to compact and smooth the surface.
The third coat of polishing (fine polishing) : Before the concrete has finally set (with no standing water on the surface and slight marks when pressed by fingers), use a trowel blade to finely grind at high speed. This step is of vital importance as it can significantly enhance the surface density and flatness, resulting in a smooth and uniform hardened surface.
Flatness requirement
When using a 2-meter straightedge for inspection, the gap should not exceed 3mm. The high-standard project requirement is ≤2mm.
The overall slope should comply with the design requirements and there should be no water accumulation areas.
Maintenance requirements
After the smoothing is completed, full curing must be carried out immediately (it is recommended to cover with plastic film or spray a special curing agent) to prevent cracking due to excessive evaporation of water. The curing period should be no less than 7 days, with 14 to 28 days being the best.
Ⅱ. Base Inspection and Treatment Before Grinding (Grinding Construction Stage)
Even a well-polished floor must undergo strict inspection and targeted treatment before grinding. This stage is usually carried out after the concrete pouring and curing are completed (at least 28 days after the strength meets the standard).
Comprehensive inspection
Strength: Tested by a rebound tester, the surface compressive strength is ≥ 25MPa. For curing agent floors, the higher the strength of the base layer, the better the final effect.
Moisture content: Detected using an electronic hygrometer. Epoxy flooring has strict requirements (the moisture content of the base layer should be ≤ 4%, or as per the requirements of the material supplier). The curing agent floor has a relatively high tolerance for moisture, but it must not have standing water either.
Flatness: Check again with a 2-meter straightedge and mark the areas that exceed the standard.
Defect inspection: Carefully examine for hollowing (by tapping with a small hammer), cracks, oil stains, floating slurry, cement lumps, exposed steel bar ends, etc.
Key processing procedures
Cleaning: Thoroughly sweep the floor and use an industrial vacuum cleaner to suck up all dust and sand particles.
Hollowing and Defect repair
Remove all hollow and loose parts.
V-shaped grooves should be made for non-structural cracks, and they should be filled and repaired with high-strength non-shrinking epoxy resin or polymer cement mortar.
The exposed ends of the steel bars on the ground should be cut to at least 3mm below the surface, then treated with anti-rust paint and filled with repair mortar.
For local pits or height differences, they should be leveled with a professional grinding machine or milling machine and then filled with matching repair materials.
Oil stain treatment: For oil stains, they must be thoroughly removed. Light oil stains can be wiped with special cleaning agents or solvents. Severely penetrating oil stains should be treated with fire roasting, milling or special degreasing agents. If necessary, the contaminated concrete should be knocked off and re-poured.
Floating slurry and weak layer treatment: This is one of the core purposes of grinding. Even on a well-polished floor, there may still be a layer of cement slurry film (floating slurry) with relatively low strength formed due to bleeding on the surface. The primary task of the grinding machine is to remove this layer of floating
Summary comparison table
| Stage | Key requirements for epoxy flooring | Key requirements for concrete hardener flooring |
| Polishing requirements | Extremely high. The denser and flatter the surface is, the better the adhesion of the epoxy coating will be and the brighter and smoother the coating effect will be. It needs to be polished to perfection. | High. The surface density directly affects the uniformity of the curing agent's penetration and the final hardening effect, and it also requires a fine finish. |
| Strength requirements | High (≥C25). The base layer is solid, and the coating is not prone to cracking due to base layer cracking. | Very high (it is recommended to be ≥C30). The strength of the base layer is the foundation of the final strength, and the curing agent is an addition reaction. |
| Moisture content requirement | Extremely strict (≤4%). Moisture can cause the epoxy coating to bubble and delaminate. | It should be relatively loose, but the ground must be dry and free of standing water. The curing agent can react with the hydration products of cement. |
| Pretreatment before grinding | The key points are absolute dryness, dust-free, oil-free and high flatness. The floating slurry layer must be removed to ensure adhesion. | The key points are to remove the floating slurry, open the pores, deal with the defects and ensure the surface is smooth. Grinding opens up channels for the penetration of curing agents. |
| Grinding particle size | Usually, grinding to 80-120 mesh is sufficient to provide adequate roughness (anchor texture) for the epoxy primer. | Usually, a coarser finish (such as starting at 30-40 mesh) is required to open up the surface, followed by multiple grinding processes to a higher mesh count (such as 1000-3000 mesh) for a brighter finish. |
Final suggestion
Communication in advance: Before the concrete pouring, the floor construction unit should conduct a detailed technical briefing with the general contractor of the civil engineering, clearly defining the plastering standards and curing requirements.
On-site supervision: The floor construction party should send personnel to supervise and guide during the concrete smoothing stage.
System treatment: Regard the base treatment as a systematic project, from pouring to curing, and then to the inspection and repair before grinding, each step is interlinked and no step can be omitted.
Professional assessment: For the renovation of old floors, a comprehensive assessment must be conducted by professionals before grinding, and a detailed treatment plan should be formulated.
Only by following the above requirements and procedures can a perfect foundation be laid for the subsequent epoxy resin coating or concrete sealant and hardener construction, thereby creating a high-performance and long-life high-quality floor.
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.
Thanks to All the Friends Who Support and Trust Shandong Vanse Machinery Technology Co., Ltd.
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About the Author: Shandong Vanse Machinery Technology Co., Ltd.
Shandong Vanse Machinery Technology Co., Ltd. is a high-tech manufacturer specializing in concrete construction machinery, including laser screeds and related equipment. The company integrates R&D, production, and global sales, with products exported to over 60 countries and widely used in infrastructure projects worldwide.
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