glass fiber reinforced cement or glass fiber reinforced gypsum, that first project tends to arrive one of a few ways:
- A client who has seen GFRC cladding on a building they admired
- A design that calls for something traditional concrete or plaster can’t deliver
- A value engineering conversation that surfaces GFRG as an alternative to heavier, more expensive options.
However it arrives, the specifier is now looking at a material category they haven’t written a spec for before. The design intent is clear. The path from intent to compliant specification is less so.
This is a common situation, and it’s navigable. What it requires is understanding how GFRC and GFRG differ from the materials architects spec more routinely — and where in the specification process those differences actually matter.
Start with the Material, Not the Product
The first thing to understand is that GFRC and GFRG are manufactured materials with properties that vary by producer. Unlike commodity materials that are specified by reference to a standard and sourced from any compliant supplier, architectural GFRC and GFRG involve a manufacturing process, attachment system, finish specification, and shop drawing coordination that are specific to the manufacturer producing the elements.
That means the specification needs to be written around performance requirements and manufacturer qualifications rather than a generic product standard:
- What flexural strength is required?
- What fire rating does the assembly need to meet?
- What surface finish — smooth, textured, integral color — is specified, and how is that finish verified before delivery?
These are the questions the spec needs to answer, and they’re questions a manufacturer like GC Products can help frame correctly before the specification is drafted.
Getting involved with the manufacturer early — ideally during design development rather than at the construction document phase — saves significant time and reduces the likelihood of a specification that requires revision after submittals are received.
What the Specification Needs to Cover
A well-written specification for architectural GFRC or GFRG addresses several areas that don’t always appear in first-time specs for these materials. Each of them affects how the submittal process goes and how smoothly installation proceeds in the field.
The areas that need to be addressed include:
- Material Composition and Performance Requirements — The spec should define minimum physical properties: modulus of rupture, tensile strength, and density for GFRC; flexural strength and hardness for GFRG. Referencing PCI MNL-130 for GFRC and relevant ASTM standards for gypsum-based products gives the contractor and manufacturer a clear performance baseline rather than relying on general language that is difficult to verify.
- Fire and Building Code Compliance — Both GFRC and GFRG have well-documented fire resistance characteristics, but the spec needs to identify what’s required for the specific assembly and occupancy. GFRG is noncombustible and commonly used in applications where fire-rated assemblies are required. GFRC exterior cladding applications have their own code considerations around attachment and drainage. The specification should reference the applicable code requirements explicitly rather than leaving them to the contractor’s interpretation.
- Manufacturer Qualifications — Specify that the manufacturer must have demonstrated experience producing the type of elements required, provide documentation of past projects of comparable scope, and maintain a quality control program. This is the section that separates manufacturers with genuine GFRC and GFRG capability from those who can produce simple shapes but lack the tooling or experience for complex custom elements.
- Shop Drawing and Submittal Requirements — Specify what the manufacturer is required to submit — shop drawings showing dimensions, attachment details, and finish samples — and what the review process looks like. For projects using BIM, specify that shop drawings be coordinated with the project model and identify who is responsible for clash detection between the architectural elements and structural or MEP systems behind them.
- Attachment and Substrate Requirements — GFRC panels and GFRG ceiling elements each have specific attachment requirements that need to be addressed in the spec and coordinated with the structural and framing drawings. For exterior GFRC, the attachment system and the drainage plane behind the cladding are critical performance elements. For interior GFRG, the substrate framing needs to be specified to support the dead load of the elements and accommodate any tolerances in the field conditions.
- Finishing, Patching, and Touch-Up — Specify the acceptable methods for field modification, patching, and touch-up of damaged elements. Both materials can be repaired in the field, but the repair materials and methods need to match the original finish. This section is often omitted from first-time specs and becomes a problem when a piece is damaged during installation.
A specification that addresses all of these areas gives the contractor and manufacturer a clear scope, reduces the back-and-forth during submittal review, and protects the design intent through the installation phase.
Where First-Time Specs Most Often Fall Short
The most common issue in first-time GFRC and GFRG specifications is underspecifying the attachment system. Architects sometimes carry the material specification without fully working out how the elements connect to the building structure — and the attachment is where the engineering, the structural coordination, and the building code requirements converge. For exterior GFRC cladding, this is particularly critical. The attachment system needs to accommodate thermal movement, transfer wind and seismic loads, and work with the waterproofing and drainage plane behind it.
The second common gap is finish specification. “Match the approved sample” is not a specification — it’s a dispute waiting to happen. Color, texture, sheen level, and acceptable variation all need to be defined before a sample is approved, and the approval process itself needs to be documented in the spec.
The third is coordination timing. GFRC and GFRG elements often have long lead times because they are custom manufactured to project-specific molds. Specifying that shop drawings are required before fabrication begins — and that fabrication cannot begin before shop drawings are reviewed and approved — protects the schedule by surfacing coordination issues before they become field problems.
How GC Products Supports the Specification Process
GC Products provides complete estimating and take-off services, shop drawing coordination in CAD, BIM, and 3D modeling, and project-specific manufacturing — which means the specification support starts well before a purchase order is issued. For architects working with GFRC or GFRG for the first time, early engagement with the manufacturer can help frame the specification correctly, identify coordination requirements that need to be addressed in the construction documents, and establish realistic lead times for the project schedule.
Product data sheets for GFRG and GFRC are available on the GC Products website, along with physical specifications and performance data that can be referenced in the project specification. For questions about a specific project or to discuss specification support, call GC Products at 916-645-3870 or reach out through the contact form on the website.