Chapter 7
Flexible Stone Performance Indicator System: From Test Reports to Engineering Value
Compiled by Guangdong Fortune Stone New Material Co., Ltd.
Key Points
- Flexible stone performance indicators are divided into three levels: material performance, system performance, and engineering performance. Test data must be translated into engineering value to be meaningful.
- Clients, design institutes, construction parties, and supervisors each focus on different indicators. Mastering the “number translation” method for different roles is essential.
- Performance indicator selection should match building type, climate environment, and project budget, avoiding the three misconceptions of “the higher the better,” “only looking at a single indicator,” and “ignoring construction.”
7.1 The “Three-Layer Logic” of Flexible Stone Performance Indicators
Flexible stone performance indicators are divided into three levels, each corresponding to different verification methods and engineering roles.
The first layer is material performance, i.e., the physical and mechanical properties of the flexible stone panel itself, such as tensile strength, flexibility, and water absorption. Material performance is determined by formula and process, and verified through factory inspection and type inspection. The second layer is system performance, i.e., the performance of the system composed of flexible stone, bonding agent, and substrate, such as bonding strength, impact resistance, and weather resistance. System performance is determined jointly by materials, bonding agents, and substrate, and verified through pull-off tests, weather resistance tests, etc. The third layer is engineering performance, i.e., the performance exhibited by materials in actual engineering, such as construction convenience, renovation convenience, and maintenance cost. Engineering performance is influenced jointly by materials, construction, and management, and verified through project measurements and cost accounting.
The relationship among the three levels is: material performance determines system performance, and system performance determines engineering performance. However, engineering performance is also affected by construction quality, environmental conditions, and use and maintenance, and final effects cannot be inferred solely from material test reports. The testing basis for flexible stone product performance includes JG/T 311 Flexible Facing Brick and JC/T 2219 Modified Inorganic Powder Composite Building Facing Sheet standards[1-2].
Table 7-1 The Three-Layer Logic of Flexible Stone Performance Indicators
| Level | Core Indicators | Determining Factors | Verification Method |
|---|---|---|---|
| Material performance | Tensile strength, flexibility, water absorption | Formula, process | Factory inspection, type inspection |
| System performance | Bonding strength, impact resistance, weather resistance | Material + bonding agent + substrate | Pull-off test, weather resistance test |
| Engineering performance | Construction efficiency, maintenance cost, renovation convenience | Material + construction + management | Project measurement, cost accounting |
Engineering case: A facade retrofit residential community used flexible stone for exterior wall renovation. Initially, the client only saw the high tensile strength in the material test report and believed the product was fine. The design institute proposed verifying the bonding system, and the construction party proposed confirming substrate moisture content. Later, a 200 m² sample wall was made; pull-off tests showed bonding strength met standards, and areas with high moisture content using breathable flexible stone showed no hollowing. The project ultimately passed acceptance smoothly.
Case insight: Material performance does not equal system performance, and even less equals engineering performance. Using sample walls to verify system performance can avoid jumping directly from test reports to engineering conclusions.
7.2 Detailed Explanation of Material Performance Indicators
Material performance indicators are the foundation of flexible stone quality, including five categories: physical, mechanical, durability, fire protection, and surface function. Each category has clear engineering significance. Fire rating is assessed according to GB 8624 Classification for Burning Behavior of Building Materials and Products[3].
7.2.1 Physical Performance Indicators
Table 7-2 Flexible Stone Physical Performance Indicators
| Indicator | Typical Value | Engineering Significance | Test Standard |
|---|---|---|---|
| Surface density | 3–5 kg/m² | Determines structural load, key indicator for facade retrofit | GB/T 17656 |
| Thickness | 3–5 mm | Affects node treatment and door/window opening | GB/T 17656 |
| Water absorption | ≤5% | Affects water resistance and freeze-thaw durability | GB/T 3810.3 |
| Bending radius | ≤20 mm | Determines whether curved surfaces can be fitted | GB/T 17657 |
| Flexibility | Bendable 90°–180° | Affects transportation, construction, deformation resistance | JG/T 311 |
| Breathability | Moisture vapor transmission rate ≥15 g/(m²·d) | Affects wall moisture discharge capacity | GB/T 17146 |
Surface density is the first key indicator in facade retrofit scenarios. Traditional ceramic tile surface density is 30–50 kg/m², dry-hanging stone is 80–120 kg/m², and flexible stone is only 3–5 kg/m². For exterior walls of the same area, flexible stone reduces weight by about 90% compared with ceramic tiles and about 95% compared with stone. For high-rise facade retrofit projects, this weight advantage directly determines whether the scheme is feasible.
Bending radius is the core indicator that distinguishes flexible stone from traditional rigid materials. A bending radius ≤20 mm means flexible stone can fit complex shapes such as cylinders, curved surfaces, and corners. Ordinary exterior walls do not require high bending radius; only irregular parts need to leverage this advantage, so there is no need to increase costs by pursuing a smaller bending radius.
Breathability is an easily overlooked but crucial indicator in facade retrofit scenarios. The substrate moisture content of facade retrofit buildings is often high. If flexible stone is not breathable, moisture inside the wall cannot be discharged, and long-term accumulation will lead to bonding layer failure, causing hollowing and detachment. Currently, the industry has developed large-particle-size high-permeability flexible stone emulsion technology. Through large-particle-size core-shell structure design, the ratio of soft shell thickness to filler particle size is increased, and the interfacial phase volume fraction is controlled within the optimal range of 15%–25%, achieving a balance between breathability and flexibility. This technology enables flexible stone moisture vapor transmission rate to reach over 15 g/(m²·d), effectively solving the moisture discharge problem of facade retrofit walls and reducing the risk of hollowing and detachment caused by high substrate moisture content.
7.2.2 Mechanical Performance Indicators
Table 7-3 Flexible Stone Mechanical Performance Indicators
| Indicator | Typical Value | Engineering Significance | Test Standard |
|---|---|---|---|
| Tensile strength | 2–5 MPa | Affects material integrity | GB/T 1040 |
| Tensile bonding strength | ≥0.3 MPa | Determines whether detachment occurs, safety bottom line | JG/T 311 |
| Impact resistance | No cracks under 3J impact | Resists hail and impact | JG/T 311 |
| Wear resistance | ≤0.1 g/1000 cycles | Affects surface durability | GB/T 17657 |
Tensile bonding strength is the first line of defense for exterior wall safety. Bonding strength test reports are the core safety signal conveyed to clients and supervisors and should be a mandatory inspection item. Bonding strength is influenced by three factors: substrate conditions, bonding agent quality, and construction process. Insufficient substrate strength, wrong bonding agent selection, and non-standard construction processes will all lead to bonding strength failing to meet standards. Therefore, bonding strength is not only a material indicator but also a system indicator.
At the material level, non-migratory flexible stone emulsion technology using reactive emulsifiers bonds emulsifier molecules to polymer particle surfaces through covalent bonds, fundamentally avoiding interface weakening defects caused by emulsifier migration, significantly improving the interface stability between flexible stone and bonding agent, and providing a materials science foundation for tensile bonding strength ≥0.3 MPa.
7.2.3 Durability Performance Indicators
Table 7-4 Flexible Stone Durability Performance Indicators
| Indicator | Typical Value | Engineering Significance | Test Standard |
|---|---|---|---|
| Artificial weathering resistance | ≥2000h (high-flexibility products up to 3500h) | Equivalent to 10–15 years in natural environment | GB/T 1865 |
| Freeze-thaw resistance | No abnormality after 100 cycles | Key indicator for northern regions | JG/T 25 |
| Salt spray resistance | No obvious corrosion after 1000h | Key indicator for coastal regions | GB/T 1771 |
| Chemical resistance | Resistant to dilute acid/alkali/salt | Applicability in industrial areas and polluted environments | GB/T 9274 |
Artificial weathering resistance is the core indicator of service life. A 2000-hour aging test is equivalent to a service life of 10–15 years in natural environment. Weathering resistance indicators should be selected according to climate conditions: southern areas with strong ultraviolet radiation should prioritize weathering resistance, and northern freeze-thaw areas should prioritize freeze-thaw resistance.
In terms of durability performance, independent research and development of high-flexibility emulsion has made important breakthroughs. This technology uses monomer pre-emulsification semi-continuous seed emulsion polymerization, introducing modified additives A and B into the core-shell structure, achieving excellent flexibility of flexible stone at -30°C, withstanding 100 freeze-thaw cycles without cracking or peeling, and weather resistance of 3500h. This breakthrough increases flexible stone’s weather resistance indicator from the industry’s common 2000h to 3500h, providing more reliable durability assurance for facade retrofit projects in cold northern regions and plateau areas with strong ultraviolet radiation.
7.2.4 Fire Protection Performance Indicators
Table 7-5 Flexible Stone Fire Protection Performance Levels
| Level | Meaning | Applicable Scenarios | Test Standard |
|---|---|---|---|
| A2 | Non-combustible | High-rise buildings, densely populated places | GB 8624 |
| B1 | Flame-retardant | Ordinary residential, commercial buildings | GB 8624 |
| B2 | Combustible | Not recommended for exterior walls | GB 8624 |
Fire rating selection should be determined based on building height and population density. High-rise buildings and densely populated places should choose A2; ordinary residential buildings can choose B1. Fire rating should not be over-configured; A2 costs more than B1, and over-configuration causes functional excess.
7.2.5 Surface Function Indicators
Table 7-6 Flexible Stone Surface Function Indicators
| Indicator | Typical Value | Engineering Significance | Test Standard |
|---|---|---|---|
| Stain resistance | Whiteness recovery rate ≥70% (modified topcoat can reach over 80%) | Affects appearance retention | GB/T 9780 |
| Water resistance | No abnormality after 168h immersion | Affects applicability in humid environments | JG/T 311 |
| Alkali resistance | No abnormality after immersion in saturated Ca(OH)₂ solution | Affects applicability to cement substrates | JG/T 311 |
The inorganic silicone resin modified acrylic emulsion technology for flexible stone topcoats, through chemical bonding, copolymerizes inorganic silicone resin with acrylate monomers, combining the weather resistance and stain resistance of inorganic silicone resin with the flexibility and bonding properties of acrylate. This technology enables the flexible stone topcoat layer to achieve a stain resistance whiteness recovery rate of over 80% and weather resistance of 3500h, significantly superior to the conventional flexible stone stain resistance requirement of ≥70%.
7.2.6 Correspondence Between Core Emulsion Technology R&D and Performance Indicators
The realization of flexible stone performance indicators is inseparable from the technical support of emulsion formulas. A complete technical chain covering “breathability—non-migration—high flexibility—topcoat function” has been formed around emulsion formulas.
Table 7-7 Correspondence Between Independent R&D Emulsion Technology Directions and Performance Indicators
| Technology Direction | Core Technology | Corresponding Performance Indicators |
|---|---|---|
| Large-particle-size high-permeability flexible stone emulsion | Large-particle-size core-shell structure, toughening agent, antibacterial flame retardant | Breathability ≥15 g/(m²·d), flexibility |
| Non-migratory flexible stone emulsion based on reactive emulsifiers | Reactive emulsifiers, covalent bonding | Water resistance, interface stability, surface quality |
| High-flexibility emulsion and preparation method | Modified additives A/B, core-shell structure | Freeze-thaw resistance ≥100 cycles, weathering resistance 3500h, -30°C flexibility |
| Inorganic silicone resin modified acrylic emulsion for flexible stone topcoats | Inorganic silicone resin copolymerization modification | Stain resistance ≥80%, weather resistance 3500h |
The four core technologies support performance indicators from different angles: large-particle-size high-permeability emulsion technology regulates the balance between breathability and flexibility from the perspective of “interfacial phase volume fraction”; reactive emulsifier non-migration technology solves surface defects caused by small molecule migration from the perspective of “interface stability”; high-flexibility core-shell structure emulsion technology achieves wide-temperature-range performance improvement from the perspective of “molecular structure regulation”; inorganic silicone resin modified topcoat emulsion technology strengthens topcoat weather resistance and stain resistance from the perspective of “organic-inorganic composite.”
7.3 The “Translation Capability” from Test Reports to Engineering Value
7.3.1 Basic Methods of Number Translation
Numbers on test reports must be translated into engineering language that clients can understand—this is the basic skill of material suppliers.
Table 7-8 “Translation” Examples of Flexible Stone Performance Indicators
| Test Indicator | Technical Language | Engineering Language | Client Language |
|---|---|---|---|
| Surface density | 3–5 kg/m² | Mass per unit area | The material is very light and will not add much load to the old building, safe |
| Bending radius | ≤20 mm | Minimum bending radius | Walls, curves, and cylinders can all be fitted without special irregular parts |
| Water absorption | ≤5% | Water absorption rate | Good water resistance; will not absorb water and expand in rain, will not crack in freeze-thaw |
| Bonding strength | ≥0.3 MPa | Tensile bonding strength | Sticks firmly, will not fall off, meets national standards |
| Weathering resistance | ≥2000h (high-flexibility products up to 3500h) | Artificial aging time | Long service life; will last more than ten years, will not fade like coatings in three to five years |
| Fire rating | A2 | Combustion performance level | Non-combustible; can be used in high-rise buildings, fire acceptance is no problem |
7.3.2 “Translation” in Real Combat Scenarios
Scenario one: The client holds a test report and asks “what does this tensile strength of 2.5 MPa mean?”
Wrong answer: “Tensile strength of 2.5 MPa means the material can withstand 2.5 megapascals of stress in tension.”
Correct answer: “You don’t need to remember this number. You just need to know: this strength ensures that flexible stone will not crack or break on its own during normal use. Like a piece of cloth, if it doesn’t tear easily when pulled, it won’t easily cause problems when applied to the wall.”
Scenario two: The design institute asks “what does a bending radius of 20 mm mean?”
Wrong answer: “A bending radius of 20 mm means the material can bend around a 40 mm diameter cylinder without breaking.”
Correct answer: “A 20 mm bending radius means that for curved walls, cylinders, and corners you design, flexible stone can be directly fitted without custom irregular parts. Design freedom is much greater than ceramic tiles.”
Scenario three: The construction party asks “is a bonding strength of 0.3 MPa enough?”
Wrong answer: “0.3 MPa is the minimum requirement of the industry standard.”
Correct answer: “0.3 MPa is the national standard requirement. As long as substrate treatment is in place, the right bonding agent is used, and compaction is in place, it can be achieved. I will provide technical briefings and on-site guidance to ensure acceptance passes.”
7.3.3 Translation Strategies for Different Roles
Table 7-9 Translation Strategies for Different Roles
| Role | Indicators of Concern | Translation Strategy | Key Script Points |
|---|---|---|---|
| Client | Fire rating, surface density | Safety + compliance | Will not fall, will not burn, will not exceed budget |
| Design institute | Bending radius, color texture | Design freedom + documented basis | Can fit curved surfaces, has atlas references |
| Construction party | Bonding strength, construction efficiency | Easy to work + no rework | Training 1–2 days, rework is on me |
| Supervisor | Hollowing rate, flatness | Acceptance basis + clear responsibility | Acceptance standards ready, record templates complete |
7.4 The “Three Matches” of Performance Indicators
7.4.1 Matching with Building Type
Table 7-10 Performance Indicator Selection for Different Building Types
| Building Type | Key Indicators | Reason | Recommended Configuration |
|---|---|---|---|
| High-rise residential | Fire rating, bonding strength | Safety first | A2, bonding strength ≥0.5 MPa |
| Low-rise residential | Weather resistance, appearance | Durability and aesthetics | B1, weathering resistance ≥2000h |
| Commercial buildings | Texture, stain resistance | Image and easy maintenance | B1, stain resistance ≥70% |
| Schools/hospitals | Environmental protection, fire protection | Health and safety | A2, VOC not detected |
| Historic buildings | Customized texture, lightweight | Appearance protection and structural safety | B1, customized texture |
7.4.2 Matching with Climate Environment
Table 7-11 Performance Indicator Selection for Different Climate Environments
| Climate Type | Key Indicators | Reason | Recommended Configuration |
|---|---|---|---|
| Southern humid and rainy | Water absorption, water resistance | Waterproof and moisture-proof | Water absorption ≤3%, no abnormality after 168h immersion |
| Northern cold | Freeze-thaw resistance, flexibility | Freeze-thaw cycles | Freeze-thaw resistance ≥100 cycles, bending radius ≤20 mm |
| Coastal salt spray | Salt spray resistance, weathering resistance | Salt spray corrosion | Salt spray resistance ≥1000h, weathering resistance ≥2000h |
| Plateau strong ultraviolet | Weathering resistance, color stability | Strong ultraviolet | Weathering resistance ≥2000h, color difference ΔE ≤3.0 |
For cold northern regions, the -30°C flexibility and 100 freeze-thaw cycle performance provided by high-flexibility emulsion technology enable flexible stone to adapt to facade retrofit projects under severe cold climate conditions. For plateau areas with strong ultraviolet radiation, the 3500h weather resistance and excellent stain resistance provided by inorganic silicone resin modified topcoat emulsion technology enable flexible stone to maintain appearance quality over the long term.
7.4.3 Matching with Project Budget
Table 7-12 Performance Indicator Selection for Different Budget Levels
| Budget Level | Material Selection Strategy | Configuration Scheme | Explanation |
|---|---|---|---|
| Sufficient | High-performance model + system scheme | A2 + full system | Optimal quality |
| Moderate | Standard model + key system | B1 + key system | No cuts in key links |
| Tight | Economical model + basic system | B1 + basic system | Hold safety bottom line |
The core principle of budget matching is “no cuts in key links”: fire rating and bonding strength directly relate to safety and should not be lowered due to budget compression; weather resistance can be appropriately adjusted according to the building’s expected service life and climate conditions; appearance texture can choose economical schemes while meeting functional requirements.
7.5 The “Three Misconceptions” of Performance Indicators
7.5.1 The Higher the Better
Excessively high indicators mean increased costs, but engineering effects may not improve proportionally. For example, a bonding strength of 0.5 MPa is already sufficient; pursuing 1.0 MPa has no practical significance. Performance indicator selection should follow the principle of “sufficient is enough” to avoid value decline caused by functional excess. When facing clients, this principle should be clearly stated as: spend money on indicators that truly affect safety, not on performance you will not use.
7.5.2 Only Looking at a Single Indicator
Flexible stone performance is a “combination punch,” and a single indicator cannot be viewed in isolation. For example, low water absorption but poor flexibility will still cause problems in freeze-thaw environments. Material performance, system performance, and engineering performance are a chain; excellent single indicators do not mean excellent system performance. When facing design institutes, this principle should be implemented as: provide complete test reports and supporting bonding systems and construction methods to form an overall solution.
7.5.3 Ignoring Construction Impact
No matter how good the material is, if construction is not standardized, it is useless. Data on test reports are results under ideal conditions, and actual engineering is greatly affected by construction quality. Test reports can only prove that materials are qualified, not that construction is qualified. Therefore, the three links of on-site acceptance, process inspection, and completion acceptance are indispensable. When facing construction parties and supervisors, this principle should be implemented as: re-inspect upon entry, make samples during construction, conduct process inspections, and conduct pull-off tests at completion, using process control to ensure final performance.
7.6 Decision Reference for Facade Retrofit Offices
Key Decision Points of This Chapter
- Material selection for facade retrofit exterior walls cannot只看 material test reports; sample walls must be used to verify the true performance of the “material—bonding agent—substrate” system.
- Performance configuration should follow the “three matches”: matching with building type, matching with climate environment, and matching with project budget.
- Fire rating and bonding strength are the safety bottom line and should not be lowered due to budget compression.
Compliance Check Items
- Verify the standard basis (JG/T 311, JC/T 2219) and report validity period of product type inspection reports.
- Verify whether the fire rating meets the requirements for building height and densely populated places (A2 for high-rise, B1 for ordinary residential).
- Upon entry, require manufacturers to provide test reports and certificates, and conduct on-site re-inspection according to local regulations.
Cost Reference Range
- Performance configuration levels directly affect material unit prices; different configurations such as fire rating and topcoat function have obvious cost differences, and specific costs are based on actual projects; 30-year life cycle cost comparison is detailed in Chapter 12.
Risk Warnings
- High substrate moisture content is the main hidden danger of hollowing and detachment in facade retrofit exterior walls; breathability indicators should be prioritized during material selection.
- Directly determining engineering effects from type inspection reports alone and ignoring construction process control is the main source of acceptance disputes in facade retrofit.
- Over-configuring fire rating and mechanical indicators increases costs and is not within the reasonable scope of “no cuts in key links.”
Replicability Judgment
- Flexible stone for facade retrofit exterior wall renovation has good replicability after completing sample wall verification and clarifying substrate treatment schemes.
- Cold northern regions and areas with strong ultraviolet radiation should verify freeze-thaw cycle times and weathering resistance indicators respectively before promotion.
Reflections on Stone, Insights on Fortune
Flexible stone performance indicators are not for “showing off skills” but for “solving problems.” Behind every number corresponds to an engineering scenario, and every scenario corresponds to a type of person who cares about it. Translate numbers into human language, translate reports into schemes; the role of material suppliers then goes beyond supply itself, becoming a technical bridge between clients, design institutes, and construction parties.
References
[1] Ministry of Housing and Urban-Rural Development. Flexible Facing Brick: JG/T 311-2011[S]. Beijing: Standards Press of China, 2011.
[2] Ministry of Industry and Information Technology. Modified Inorganic Powder Composite Building Facing Sheet: JC/T 2219-2014[S]. Beijing: China Building Materials Industry Press, 2014.
[3] General Administration of Quality Supervision, Inspection and Quarantine, Standardization Administration of China. Classification for Burning Behavior of Building Materials and Products: GB 8624-2012[S]. Beijing: Standards Press of China, 2013.