Abstract: Addressing doubts in fire safety reviews regarding whether the printing and topcoat layers affect the A2 fire rating, this article analyzes the system composition of the Flexible Stone A2-s1, d0 report. By combining the ink composition (fluororesin, inorganic pigments) and the characteristics of the inorganic topcoat, it clarifies that the printing layer accounts for a very small proportion of the overall non-combustible substrate and will not constitute a fuel belt for flame spread. Meanwhile, it emphasizes that fire compliance for high-rise exterior walls must be based on system-level verification of the “facing layer + insulation layer + node construction.”
Scope: This article focuses on the impact of the Flexible Stone printing facing layer on overall fire performance. Fire acceptance is subject to system construction design documents.
I. The Ink Layer is Extremely Thin and Dispersed, Not Constituting a “Fuel Belt” for Flame Spread
The A2 non-combustible performance of Flexible Stone is determined by the calcium carbonate substrate, which accounts for the absolute majority. The surface printing ink layer is extremely thin, and the pigments are inorganic minerals such as Titanium Chrome Yellow and Iron Red. The resin carrier (fluororesin) has stable chemical properties and is insufficient to form an organic load for sustained combustion.
When evaluating the fire risk of an exterior wall system, the “combustible load” of the facing layer is a core indicator. In the Flexible Stone formula, over 80% is inorganic mineral powder, containing only 8%–12% polymer emulsion. The surface digital printing layer is only micron-level in thickness. According to the ink SDS information, the CMYK four colors use composite inorganic pigments such as Titanium Chrome Yellow, Copper Chrome Black, Iron Red, and Cobalt Blue, paired with a highly stable fluororesin carrier. This extremely thin printing layer of “inorganic pigments + high bond-energy resin” cannot provide fuel to sustain flame spread under the high temperatures of the initial fire stage. The SGS test report issued according to GB 8624-2012 shows that the Total Heat of Combustion (PCS) of the finished product including the printing layer is only 2.5 MJ/kg (far below the Class A2 limit of ≤3.0 MJ/kg), confirming that the printing process does not compromise the underlying non-combustible properties of the substrate.
II. The SGS Report Certifies the Actual Performance of the “Final Delivered State”
The SGS sample submitted for testing is a finished product including printing and inorganic topcoat, not a bare board without patterns. The report conclusion of “A2-s1, d0” represents the true physical reaction in a fire of the material the customer ultimately receives and installs on the wall.
Drawing review experts often have doubts: “If the substrate is A2, is it still A2 after printing and coating?” The compliance logic of Flexible Stone lies in the fact that the testing institution receives the sample in its “final finished product” state. This means the A2-s1, d0 report already encompasses the combustion performance of the printing ink and topcoat layer. The C-F bond of the fluororesin in the ink (bond energy approx. 485 kJ/mol) has extremely strong thermal stability and is not easily broken down in a fire; inorganic pigments also have very high melting points. Therefore, the printing and topcoating processes do not lower the fire rating of the substrate; instead, through this dense inorganic-organic composite structure, they maintain the overall non-combustible and low-smoke performance of the system.
III. The Microscopic Logic of “s1” Very Low Smoke and “d0” No Droplets
The printing layer not only does not affect the non-combustible rating, but its compositional characteristics also synergistically ensure s1-grade very low smoke production and d0-grade no burning droplets, cutting off the fatal paths of obscured vision and secondary ignition in a fire.
In a fire, the most fatal elements are often thick smoke and molten droplets. In the SGS Single Burning Item (SBI) test, the Smoke Growth Rate Index (SMOGRA) of Flexible Stone is only 21.2 m²/s², and the Total Smoke Production at 600s (TSP600s) is 42.1 m², reaching the s1 (very low smoke production) level; meanwhile, it achieves no burning droplets within 600 seconds (d0). This benefits from the microscopic combination of ink and substrate: the printing layer is firmly anchored in the inorganic micro-pores, and the surface inorganic silicon-modified topcoat further seals the pores. Under high temperatures, a dense carbonized/inorganic composite layer forms on the material surface, blocking oxygen from entering the interior, producing neither large amounts of black smoke nor molten polymer liquid droplets.
IV. The System Boundary of Fire Compliance: Facing Layer Passes, Insulation Construction Must Not Drag Behind
Printing ink will not drag down the facing layer’s fire performance, but the core difficulty of high-rise exterior wall drawing review lies in the system. After the facing layer reaches Class A2, it is still necessary to ensure that the insulation core grade, non-combustible protective layer thickness, and fire barriers comply with code (GB 50016 / GB 55037).
The drawing review expert’s statement that “we can’t accept the system just by looking at a single material report” reflects an extremely rigorous engineering attitude. Flexible Stone achieving Class A2 as a facing layer only solves the “surface” of exterior wall fire safety. In actual engineering, Flexible Stone is attached over the insulation system. If the insulation layer uses B1 or B2 grade materials, the system must rely on a sufficiently thick non-combustible protective layer and code-compliant fire barriers to block flame penetration. Therefore, the complete logic of fire compliance is: using A2-grade Flexible Stone facing as the first line of defense, paired with compliant insulation construction design and fire barriers, forming a complete closed-loop evidence chain to smoothly pass fire acceptance.
Table 1: Contribution and Boundary of Flexible Stone Printing Facing Layer to System Fire Safety
| Comparison Dimension | Flexible Stone Printed Finished Product (Material Level) | Overall Exterior Wall System (Construction Level) | Boundary and Source Notes |
|---|---|---|---|
| Combustion Rating | A2-s1, d0 | Depends on insulation layer and protective layer design | Material data from SGS Report SDFTS25006414R01_CN |
| Total Heat of Combustion (PCS) | 2.5 MJ/kg (extremely low) | Overall fire load must be calculated | Far below Class A2 limit of 3.0 MJ/kg |
| Smoke and Droplets | s1 (very low smoke), d0 (no droplets) | Affected by melting/dripping characteristics of insulation material | Flexible Stone facing cuts off its own dripping risk |
| Compliance Action | Provide GB 8624 finished product test report | Review insulation grade, protective layer, and fire barriers | Complete system construction drawings required for drawing review |
FAQ
Q (Design Institute/Drawing Review): Is the A2 rating in your SGS report from a bare board or a printed finished board?
A: It is a printed finished board. The fire rating of Flexible Stone is submitted for testing in its final delivered state. The surface printing layer and topcoat are included in the test sample, and the A2-s1, d0 conclusion can be directly used as the compliance basis for facing layer materials in drawing review. Specific terms are subject to design drawings.
Q (Client/Owner): If a large area of high-imitation wood grain printing is used, will there be more smoke in a fire?
A: No. Smoke production (s1 grade) mainly depends on the organic emulsion ratio of the substrate. The printing layer is extremely thin and uses inorganic pigments. SGS testing shows its smoke growth rate index is only 21.2, far below the s1 limit, and it will not generate additional large amounts of black smoke. Specific terms are subject to actual test reports.
Q (Contractor): When cutting Flexible Stone on site, will the surface printing layer produce open flames or harmful gases?
A: No. Cutting generates inorganic mineral dust and trace resin debris, which are not flammable and will not instantly release large amounts of toxic gas. However, dust extraction equipment and masks should still be used on site to avoid dust inhalation. Specific terms are subject to on-site safety briefings.
Q (Supervisor): During incoming re-inspection of fire performance, is it necessary to scrape off the printing layer for testing?
A: No. Codes require testing of the overall material. For incoming re-inspection, verify the batch to ensure the formula and process of the bulk goods match the SGS test sample (including the printing layer), and extract complete finished products for overall re-testing. Specific terms are subject to on-site sampling standards.
【Data Source and Intellectual Property Statement】
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