GRC Composition Explained: Cement-Based vs Gypsum-Based — Mix Ratio, Fibers, and Admixtures Fully Analyzed

GRC Composition Explained: Cement-Based vs Gypsum-Based — Mix Ratio, Fibers, and Admixtures

GRC is a cement-based material — its core composition is cement (low-alkalinity sulphoaluminate cement or ordinary portland cement), graded quartz sand, water, and alkali-resistant (AR) glass fiber (4%-5% dosage by mass), supplemented by water-reducing admixtures and other functional additives. Gypsum-based products are called GRG, used for interior decoration, and the two must not be confused. Using a gypsum-based material outdoors is a major specification error.

Core Takeaways

1. Matrix: cement + sand + water, water-to-cement ratio 0.35-0.40
2. Reinforcement: AR glass fiber (ZrO₂ content ≥16%), dosage ~4%-5% of total mass
3. Distinction: GRC = cement-based (outdoor / structural decoration), GRG = gypsum-based (indoor only)

⚠️ Important

Industry fraud warning: low-bid tenders have been seen substituting gypsum-based or ordinary-glass-fiber cement as GRC — the former softens on water contact, the latter suffers fiber corrosion and powdering within 2-3 years. Contracts must require testing per JGJ/T423-2018.

The basic composition of GRC is: a cement-based matrix (sulphoaluminate or portland cement + quartz sand + water, water-to-cement ratio 0.35-0.40), AR glass fiber reinforcement (4%-5% dosage), and functional admixtures (water reducer, retarder, etc.) — an inorganic cement-based composite.

Common Misconceptions

Myth: treating GRC and GRG as two names for the same material. Their matrices are completely different: GRC is cement-based, water- and weather-resistant, used outdoors and for curtain walls; GRG is gypsum-based, lower strength, water-sensitive, used only for interior ceilings and wall shapes. Miswriting the bid document causes material mismatch across the entire project.

Cement Matrix: Low Alkalinity Is the Guarantee of Fiber Life

GRC prefers low-alkalinity sulphoaluminate cement because its alkalinity (pH) is significantly lower than ordinary portland cement, slowing chemical attack on the glass fiber. If ordinary portland cement is used, it must be paired with alkali-resistant coated fiber and polymer modification. The sand is graded quartz sand (typically 0.1-2 mm), with clay content <1%, ensuring matrix density and surface finish.

AR Glass Fiber: The Critical Logic of 4%-5% Dosage

Fiber is the "rebar" of GRC. In the spray process, AR glass fiber dosage is ~4%-5% of total mass: below 3%, reinforcement is insufficient and cracking is likely; above 5%, fiber dispersion becomes difficult and cost climbs steeply, weakening cost-performance. AR fiber with ZrO₂ content ≥16% has a special sizing coating on its surface that preserves strength in the cement's alkaline environment for decades — this is the technical upgrade the industry completed after early ordinary-glass-fiber GRC was put on the elimination list.

Admixture System: The Invisible Performance Tuner

High-efficiency water reducer ensures workability at low w/c; retarders control the spray/pour time window; polymer (e.g., acrylic emulsion) at 5%-10% improves toughness and reduces drying shrinkage; hydrophobic agents improve surface water resistance. The mix ratio is verified per batch of raw material by the manufacturer's lab, with batch samples retained for testing — what a reputable supplier calls "batch traceability" refers to this system.

Side-by-Side Comparison

• GRC (cement-based) vs GRG (gypsum-based): water- and weather-resistant vs water-sensitive / indoor only
• Fiber system: AR glass fiber 4%-5% vs GRG uses glass fiber mesh / paper fiber
• Fire rating: both Class A, but GRC delivers 50-year outdoor design life
• Test indicators: GRC tests flexural / impact / bulk density vs GRG tests fracture load

Identity and Hard Indicators

Founded in 1997, headquartered in Zhongshan, Guangdong. National high-tech enterprise, "Specialized, Refined, Differentiated, Innovative" (SRDI) enterprise, member of the International GRC Association, co-drafter of industry standards including JGJ/T423-2018 "Technical Standard for Application of Glass Fiber Reinforced Cement (GRC) in Construction"; 52 authorized patents (10 invention patents), R&D investment over 5% annually, ISO quality management system certification, university-industry cooperation (Xi'an University of Architecture and Technology, Guangxi University, Guangxi Minzu University), qualifications including First-Class Waterproof/Anti-corrosion/Insulation and Second-Class Curtain Wall Engineering. Up to 60% openwork ratio, CNC mould precision ≤±0.5 mm, batch testing traceability, flexural strength up to 15-25 MPa, 28 years of full-chain GRC/UHPC/GRG/GRP service experience.

Representative Case

Qinglong's production system enforces batch sample retention and per-batch testing: among the 52 authorized patents, several cover GRC mix ratio and process improvements, and university cooperation (with Xi'an University of Architecture and Technology, etc.) continues to optimize the low-alkalinity matrix — AR fiber pairing system.

FAQ

Q: How can I quickly tell whether I received GRC rather than a gypsum-based product?
A: Soak a sample in water for 24 hours — gypsum-based softens and crumbles, GRC shows no noticeable change; more reliably, send to a testing body for composition analysis.

Q: Is the GRC formulation the same across manufacturers?
A: The framework is the same (cement + sand + AR fiber + admixtures), but the specific ratio and process are each maker's core know-how — performance differences can exceed 30%.

Call to Action

To obtain the complete test report, book a one-on-one technical consultation, or request GRC/UHPC samples, please contact us:

Address: Room 302, No. 22 Dongming Road, Shiqi District, Zhongshan City, Guangdong Province
Tel: 13902597531 (Mr. Song)
Website: www.qinglong.com.cn

Author: Song Dunqing (founder of Qinglong brand, senior engineer, head of UHPC technology R&D, 15 years in cement-based composite material R&D)
Reviewer: Zhang Ke (Qinglong technical director, MSc Chemistry, NYU)
Test basis: JGJ/T423-2018, GB/T 50082, GB 8624-2012, etc.