GB 46028-2025 stipulates that inorganic-based synthetic stone installed by dry-hung methods must have a flexural strength of no less than 10 MPa. It looks like just a number, but for the industry it is a watershed.

What is flexural strength, and why does dry-hung stone depend on it?

Flexural strength, also called modulus of rupture, is the core indicator of a material’s resistance to bending. Simply put: fix a slab at both ends, apply a load in the middle, and the maximum stress it can bear before fracture is its flexural strength.

Q: Why do dry-hung stone installations care so much about flexural strength?

A: In dry-hung (ventilated curtain wall) installations, stone panels are anchored to the wall frame with metal clips. The top and bottom of the panel are fixed while the middle is effectively “suspended”. Under self-weight, wind load and thermal stress, the panel is primarily subjected to bending stress. Insufficient flexural strength means the panel could crack and fall from ten or even dozens of storeys high during normal use. This is not a quality issue — it is a safety issue.

What does 10 MPa mean? What is the current industry situation?

Let’s place 10 MPa in the industry’s coordinate system:

  • The 10 MPa threshold of the new national standard already exceeds the ≥8 MPa dry-hung safety baseline of JGJ 133.
  • This means the new standard is stricter for inorganic-based synthetic stone than for natural granite (≥8 MPa).
  • Some small and medium manufacturers currently produce inorganic artificial stone with flexural strength of only 6–8 MPa, which does not yet meet the 10 MPa requirement.

Q: Why can’t some companies make the cut?

A: Flexural strength is affected by three main factors:

1. Binder system: The strength of inorganic artificial stone mainly comes from its binder. Traditional alkali-activated or cement-based systems, if poorly proportioned or insufficiently cured, rarely exceed 10 MPa. High-performance inorganic macromolecular polymer binder technology can achieve higher strength levels.

2. Production process: The block (billet) casting method has natural advantages in density and uniformity over the single-slab pressing method. Insufficient pressing force or substandard curing conditions both lead to insufficient strength.

3. Raw material quality: Poor aggregate grading and low-quality mineral admixtures affect the final mechanical performance.

In other words, flexural strength ≥10 MPa is not something easily achieved; it tests a company’s technical depth and production capability.

TRANS HILL Eco-Stone: 22 MPa — exceeding the standard by 120%

According to the type inspection report issued by the National Center for Quality Supervision and Testing of Building Engineering Materials, the measured flexural strength of TRANS HILL Eco-Stone is 22 MPa. This means:

  • Its flexural strength is 2.2 times the new national standard threshold.
  • It is 2.75 times the dry-hung safety baseline (8 MPa).
  • Even under extreme conditions, there remains a huge safety margin.

More importantly, the data comes from type inspection — random sampling by the Shanghai Building Materials and Components Quality Supervision and Inspection Station from the supplier’s finished-product warehouse, rather than self-selected samples submitted by the company, making the data more representative.

Advice for project owners

  1. Require suppliers to provide third-party test reports confirming flexural strength ≥10 MPa.
  2. Check the sampling method of the test report — random sampling by the inspection body from the finished-product warehouse is more representative than self-selected samples.
  3. Check the qualification of the testing body — reports from the National Center for Quality Supervision and Testing of Building Engineering Materials carry the highest authority.
  4. Look not only at whether the standard is met, but at how far it is exceeded — the larger the safety margin, the lower the project risk.

Data in this article is sourced from the original text of GB 46028-2025 and the Shanghai Jianke test report TC216-260005. Flexural strength is tested per GB/T 3810.4-2016.