Self-Leveling Mortar

There are many types of self-levelling mortars, which are typically classified based on three core criteria: binder, application, and application thickness:

1. Classification by Binder (Most Common Classification)

This is the key factor determining the mortar’s performance and suitable applications:

• Cementitious Self-Levelling Mortar:
  • Features: High strength, high hardness, and good water resistance.
  • Disadvantages: Relatively high drying shrinkage; improper application can easily lead to fine cracks.
  • Applications: Damp environments (basements, bathrooms), high-traffic areas (warehouses, garages), or as a substrate for tile installation.
• Gypsum-based Self-Leveling Mortar:
  • Characteristics: No shrinkage, no cracking, extremely high flatness, wide range of application thicknesses (can be applied thickly).
  • Disadvantages: Sensitive to water; cannot be used in environments with prolonged moisture.
  • Applications: Backfilling for underfloor heating in home renovations, leveling for wood flooring, and renovation of older homes.

2. Classification by Function

Underlayment Self-Leveling Compound:

• Purpose: Serves as an “intermediate layer.”
• Requirements: Primarily provides levelness; the surface cannot be used directly and must be covered with wood flooring, carpet, or tiles.

Topping Self-Leveling Compound:

• • Purpose: Serves as the “finishing layer.”
  • Requirements: Must possess extremely high abrasion resistance and compressive strength, with an aesthetically pleasing color; typically used directly as a floor surface when paired with a topcoat (clear varnish). Commonly used in industrial-style offices, exhibition halls, and high-standard cleanrooms.

3. Classification by Application Thickness

• Thin-Layer Self-Leveling Compound: Thickness typically ranges from 2mm to 5mm. Primarily used for fine leveling, requiring a high-quality subfloor.
• Thick-Layer Self-Leveling Compound: Thickness can reach 10mm to 50mm. Commonly used for underfloor heating backfill or floors with significant elevation differences; currently, gypsum-based thick-layer self-leveling compounds are the mainstream option.

4. Specialty Self-Leveling Compounds

Colored Self-Leveling Compounds: Achieve a variety of decorative colors, such as red, green, and gray, by adding inorganic pigments.

Anti-Static Self-Leveling Compounds: Contain conductive fibers and are used in special environments requiring anti-static properties, such as electronics factories and server rooms.

1. Inadequate Substrate Preparation (Main Cause)

• Cause: The floor substrate is loose or contains micro-pores; when the mortar is poured, air is forced out, forming bubbles.
• Solution: It is essential to apply a primer (base coat). The primer seals the capillaries in the substrate to prevent gas from rising and simultaneously enhances adhesion. It is recommended to apply two coats to ensure no areas are missed.

2. Issues with the Selection or Dosage of Defoamers

• Cause: Self-leveling compounds contain components such as Redispersible Polymer Powder and cellulose ether, which are highly prone to generating mechanical bubbles during mixing. If the defoamer in the formulation is of poor quality or insufficient in quantity, the bubbles cannot burst on their own.
• Countermeasures: Select a highly effective powdered defoamer (such as polyether or silicone-based). During laboratory formulation testing, ensure the defoamer can rapidly eliminate foam generated during mixing.

3. Improper Mixing Process

• Cause: Excessive mixing speed or an improperly shaped mixing head, resulting in the incorporation of too much air; or pouring the mixture directly without allowing it to settle and release air after mixing.
• Solution: Use a low-speed, high-power mixer. After mixing thoroughly, let the mixture settle for 2–3 minutes to allow large bubbles to dissipate naturally before application.

4. Omission of the Defoaming Step During Application

• Cause: Failure to use specialized tools after spreading the slurry.
• Countermeasure: It is mandatory to use a de-foaming roller (spiked roller). While the slurry is still fluid, roll it back and forth in the direction of application to forcefully puncture bubbles both within and on the surface of the slurry.

5. Impact of Construction Environment

• Cause: Excessively high ambient temperature or direct exposure to strong winds causes the surface to skin over too quickly, trapping internal bubbles that cannot escape.
• Countermeasure: Close doors and windows during application to prevent drafts, and maintain an indoor temperature between 5–30°C.

Remedial Measures:

• If a large number of bubbles are discovered after the material has completely dried: The surface layer must be ground down using a grinder. After removing dust, apply a thin layer of self-leveling compound or use wall putty to level the surface.

Self-levelling mortar is described as “technologically advanced” because, among building materials, it is a classic example of a “precision chemical”. Unlike traditional cement mortar, which simply involves mixing sand and cement, self-levelling mortar is an extremely sensitive, multi-component balanced system.

Its technological sophistication is primarily reflected in the following core challenges:

1. Extremely Stringent Rheological Control

• Self-Leveling vs. Slump: Ordinary concrete only needs to hold its shape, but self-leveling mortar requires the mixture to flow automatically like water.
• Dynamic Equilibrium: The technical challenge lies in how to achieve ultra-high flowing properties while maintaining a low water-cement ratio (to ensure strength). This requires precise adjustment of the ratios of superplasticizers, cellulose ethers, and rheology modifiers; adding just one gram too much causes bleeding and sedimentation, while one gram too little renders the slurry immobile.

2. “Zero Shrinkage” and Crack Control

• Volumetric Stability: Cement-based materials naturally shrink as they dry. Since self-leveling screeds are typically only a few millimeters thick, any shrinkage can result in spiderweb-like cracks or detachment from the substrate.
• Compensation Technology: High-quality self-leveling compounds require a complex ternary system formulation—incorporating high-alumina cement, gypsum, and expansive agents—to achieve “shrinkage compensation” and deliver a seamless finish visible to the naked eye.

3. Performance Changes Within an Extremely Short Timeframe

• Application Window: The mixture must maintain liquid-like flowability (without skinning) for 20–30 minutes after mixing.
• Rapid Hardening: Once applied, the material must rapidly develop strength within 4–6 hours to reach a hardness suitable for foot traffic. This contradictory control of “slow initial setting followed by rapid final hardening” places extremely high demands on the synergy of chemical additives.

4. Complex Multi-Component Synergy (Formulation Science)

A mature self-leveling formulation typically contains 10–15 raw materials:

• B Binding MaterialsB : The proportions of Portland cement, high-alumina cement, and anhydrous gypsum determine the strength.
• B Functional AdditivesB : Defoamers, retarders, earlyaccelerators, dispersible polymer powder, wetting agents, etc.
• Physical and chemical reactions occur between these additives; even a slight variation in the purity of a single additive can cause bubbles to form or the surface to powder during application.

5. Technology for Adapting to Substrates

• Self-leveling mortar must not only be strong in itself but also be able to “grip” existing floors. This involves interfacial science; one of the core technologies is how to use Redispersible Polymer Powder to form a flexible polymer film during the drying process, thereby enhancing adhesion to various substrates.

Summary:

Self-levelling mortar is not the product of “brute force,” but rather a combination of materials science and engineering. It has an extremely low tolerance for errors in raw material stability (such as sand gradation and cement reactivity) and formulation precision; even the slightest deviation can lead to construction failures.