Self Leveling Compound-Flooring Mortar-Grout

CHARING manufactures HPMC, RDP, and PCE for dry-mix mortar and concrete — supplying high quality products across Southeast Asia, the Middle East, South America and Africa for over a decade. We share what we know.

1. What Is Self-Leveling Compound?

Self-leveling compound (SLC) is a dry-mix mortar that flows flat under its own weight. You pour it, it spreads, and it forms a smooth, level surface. No troweling needed.

It is the most formulation-sensitive product in dry-mix mortar. Tile adhesive has margin for error. SLC does not. Four binders must balance perfectly, or the whole system fails.

2. Standards and Codes

Key requirements from JC/T 985-2005: initial flow ≥130 mm, 28-day compressive strength ≥20 MPa, flexural ≥4 MPa, bond ≥1.0 MPa, dimensional change ≤0.10%.

3. Types of Self-Leveling Compound

By Layer Thickness

Cement-Based vs Gypsum-Based

4. The Binder System — Why It Is a Balancing Act

A single cement type cannot meet SLC's demands — fast setting, volume stability, controlled strength. The most common system is the ternary blend:

Portland cement + calcium aluminate cement (CAC) + gypsum.

These three react to form ettringite, the key to SLC:

Forms rapidly → fast setting and early strength

Holds lots of water (~46% by weight) → reduces free water, less shrinkage

Expands slightly → compensates cement shrinkage, prevents cracking

The ratio must be balanced. Typical: OPC 250–350 : CAC 50–100 : gypsum 30–50 kg/t.

Too much ettringite = expansion cracking. Too little = shrinkage cracking. This balance is why SLC is hard to get right.

Why the balance matters — shrinkage vs expansion.

Cement shrinks as it cures and dries. If nothing cancels it out, the floor cracks. Ettringite expands, which offsets that shrinkage. That is the whole reason the ternary system exists — to balance shrink against expand.

A simpler option.

You do not always need the full ternary system. A suitable expansive agent can also compensate the shrinkage — in self-leveling compound and in grout. This lets you run a much simpler formula.

The right expansive agent, and the right dosage, depends on your cement and your sand. So we do not go into that here — each company should test its own. Our role is to supply the additives (PCE, HPMC, RDP) that make whichever system you choose work.

5. The Six Key Additives

Why low-viscosity HPMC? SLC needs flow AND water retention. High-viscosity HPMC (100,000–200,000 mPa·s, used in tile adhesive) makes the mix too thick to self-level. Low-viscosity HP 400 (400 mPa·s) holds enough water without killing flow.

Why defoamer matters so much here? SLC is thin, so it traps air easily during mixing. Without defoamer, the surface is covered in pinholes — a defect that also weakens the surface. This is the most underrated additive in SLC.

6. Reference Formula — Cement-Based Underlayment (Ternary System)

7. Performance Requirements (JC/T 985-2005)

8. CHARING Product Recommendations

9. Common Defects and Fixes

10. Common Mistakes to Avoid

1. Using high-viscosity HPMC. SLC needs flow. High-viscosity HPMC (like tile adhesive grades) kills it. Always use HP 400 (400 mPa·s).

2. Skipping the defoamer. SLC traps air. No defoamer = pinhole-covered surface. It is the most underrated additive.

3. Wrong CAC-to-gypsum ratio. Too much gypsum = uncontrolled expansion. Too much CAC = flash set. Balance is everything.

4. Ignoring substrate prep. SLC peels off unprepared floors. Always prime first.

5. Fear of higher PCE. More PCE lets you cut water, which helps both flow and final strength. Do not be afraid to raise PCE.

For technical support, free samples, or help with your self-leveling formula:

Shandong Charing Industry Co., Ltd. 

Email: info@sdcharing.com 

Website: www.sdcharing.com