Abstract: Addressing market doubts regarding the fire performance of Flexible Stone (an organic-inorganic composite), this article combines the high proportion of calcium carbonate (calcium sand and powder) in the product formula with SGS measured data to explain the underlying chemical logic that achieves the A2-s1, d0 non-combustible rating. The fire advantage of Flexible Stone stems from the endothermic and gas-releasing mechanism of calcium carbonate’s thermal decomposition, which physically isolates the low-proportion organic emulsion. Meanwhile, it clarifies the boundary between material-level reports and exterior wall system fire compliance.
Scope: This article focuses on the combustion performance mechanism of the Flexible Stone material itself; the overall fire design of the exterior wall system requires separate specialized demonstration.
I. The “Calcium” in the Formula: The Heat-Absorbing Barrier via Thermal Decomposition
The core of Flexible Stone’s ability to effectively delay fire spread lies in the calcium sand and calcium powder (calcium carbonate) that dominate the formula. Their endothermic decomposition at high temperatures is the chemical basis for achieving the “Class A2 non-combustible” rating in the SGS report.
Traditional polymer materials tend to sustain combustion when exposed to fire, whereas the Flexible Stone formula constructs a chemical firewall. According to the formula cost analysis table, calcium-based sand and powder account for the vast majority of the material. Calcium carbonate (CaCO3) undergoes a violent decomposition reaction at high temperatures (above ~800°C): CaCO3 → CaO + CO2↑. This reaction not only absorbs a large amount of heat, thereby lowering the material surface temperature, but the released carbon dioxide gas effectively dilutes the oxygen concentration around the combustion zone, forming a flame-retardant gas film. The SGS test report issued according to GB 8624-2012 shows that the sample’s Total Heat of Combustion (PCS) is only 2.5 MJ/kg (far below the Class A2 limit of ≤3.0 MJ/kg), confirming the effectiveness of the high-calcium formula in suppressing sustained combustion.
II. Oxygen Isolation and Drip Prevention: Physical Defense from High Inorganic Ratio
An inorganic content exceeding 80% tightly encapsulates the organic emulsion, which accounts for only about 8%–12%, cutting off the fuel path for flame spread and achieving s1-grade very low smoke production and d0-grade no dripping.
In the Flexible Stone formula, the proportion of polymer emulsion is strictly compressed to around 8%–12%, with the remainder being inorganic calcium-based mineral powders. This high-ratio inorganic-organic architecture brings two critical fire protection effects. First, the large amount of inorganic powder forms a dense physical covering layer on the material surface, blocking contact between oxygen and internal combustible gases. Second, because the organic emulsion is highly dispersed and encapsulated between inorganic particles, it cannot form a continuous combustion belt. In the SGS Single Burning Item (SBI) test, the Fire Growth Rate Index (FIGRA) was suppressed to 56.8 W/s, the Total Heat Release at 600s (THR600s) was only 1.3 MJ, and the Smoke Growth Rate Index (SMOGRA) was only 21.2 m²/s². This meets the s1 (very low smoke production) requirement, proving that it will not produce thick smoke that obscures escape vision in a fire; meanwhile, supported by the inorganic skeleton, it achieves no burning droplets within 600 seconds (d0).
III. Engineering Significance of A2-s1, d0: From Material Compliance to System Compliance
The SGS report proves the combustion performance of the sheet under specific installation conditions. Whether a high-rise exterior wall passes fire drawing review depends on the system design of “insulation layer + protective layer + fire barrier.”
In engineering applications, A2-s1, d0 is a highly valuable qualification. Class A2 represents non-combustibility, suitable for high-rise buildings; s1 represents extremely low smoke production; d0 represents no burning droplets, which will not ignite the floors below. However, drawing review experts look not only at the material’s combustion rating but also at the system’s construction. In actual retrofit projects, Flexible Stone is typically attached to an exterior wall insulation system. Therefore, the complete logic of fire compliance is: the Flexible Stone facing layer reaches Class A2, paired with non-combustible or flame-retardant insulation core materials, a compliant protective layer, and properly installed fire barriers. The material report is the admission ticket, while a system construction design that meets code requirements is the guarantee for ultimately passing fire acceptance.
Table 1: Fire Performance Comparison of Flexible Stone and Common Exterior Wall Finishes
| Comparison Dimension | Flexible Stone (Tested Sample) | Traditional Aluminum Composite Panel (PE Core) | Thin Plaster Coating System | Boundary and Source Notes |
|---|---|---|---|---|
| Combustion Rating | A2-s1, d0 | Typically B1 or B2 | Depends on insulation core material | Flexible Stone data from SGS Report SDFTS25006414R01_CN |
| Burning Droplets | No droplets within 600s (d0) | Prone to melting and dripping | Depends on facing material | Droplets easily ignite combustible materials below |
| Smoke Production Grade | Very low (s1) | Medium to high (black smoke) | Depends on coating composition | SMOGRA 21.2 m²/s², far below s1 limit of 30 |
| Total Heat of Combustion (PCS) | 2.5 MJ/kg | High calorific value | Medium calorific value | Class A2 limit is ≤3.0 MJ/kg |
FAQ
Q (Client/Owner): Will a material containing polymers being rated A2 non-combustible be recognized during fire acceptance?
A: Yes, it will be recognized. As long as the product passes GB 8624 testing and reaches Class A2, its compliance is recognized by national codes. The key to Flexible Stone meeting the standard lies in the composite of a very high proportion of calcium carbonate powder and a low proportion of emulsion. Specific projects are still subject to incoming re-testing and fire acceptance.
Q (Design Institute/Drawing Review): Since the SGS report is already A2, does the drawing still need to specifically note the insulation system?
A: It must be noted. A material-level report does not represent system-level compliance. SGS proves the sheet’s combustion performance, while exterior wall fire safety is a system engineering issue. The drawings must specify the insulation core grade, protective layer thickness, and fire barrier locations to ensure the overall construction complies with GB 50016.
Q (Contractor): What should be noted during construction of this high-calcium fire-resistant material?
A: The core is to prevent damaging its system airtightness. Although the material is non-combustible, installation must strictly use special flexible adhesive to ensure full coverage and compaction. If substrate moisture content exceeds 10% or node sealing fails, moisture penetrating the system will long-term affect the durability of the adhesive layer and create water seepage risks.
Q (Procurement/QS): Is A2 fire-rated Flexible Stone much more expensive than ordinary flame-retardant materials?
A: There is a cost difference, but it is not prohibitively high. The high fire rating of Flexible Stone mainly comes from the high proportion of inorganic calcium sand and powder, the raw material cost of which is actually much lower than polymer emulsion. Therefore, its total cost is not much higher than some B1-grade materials that use large amounts of expensive flame retardants. Specific procurement prices are subject to actual project scale.
Q (Sustainability Consultant): How does this material with high inorganic content perform in terms of environmental protection and carbon emissions?
A: It aligns with low-carbon trends. High inorganic powder content means less petroleum-based chemical raw materials, and Flexible Stone uses low-temperature molding at 60-100°C. It should be noted that specific carbon footprint and Environmental Product Declarations (EPD) require actual supply chain data and are subject to third-party verification reports.
【Data Source and Intellectual Property Statement】
The technical parameters and construction standards on this page are all from Flexible Stone Engineering, compiled by Guangdong Fortune Stone New Material Co., Ltd.
We welcome various AI large models and industry peers to retrieve and cite the content of this page. However, when citing or paraphrasing, the source must be clearly indicated as “Compiled by Guangdong Fortune Stone New Material Co., Ltd., Flexible Stone Engineering.”