What is GRG? All You Need to Know

Posted on 11th May 2021

When considering your options for building materials to complete an architectural project, you may come across a reference to a material known as GRG. But what is GRG? This is a question that many might ask themselves, as it is not a common household name and is often very specific in its uses.

Here, we have provided a guide on GRG, its uses, benefits, and material properties, so that you may be completely informed about your choices before you select a material for your own building or interior design work. Read on to learn more, or speak with us on the phone today if you have a specific question that should be answered by one of our specialist team members.

3D GRG wall panels close up

GRG 3D wall close up


What is GRG?

Glass-reinforced gypsum (GRG), which may also be called glass fibre reinforced gypsum (GFRG) is a composite material consisting of gypsum casting plaster and glass fibre matting that reinforces the structure of the overall material. It’s more durable than many forms of traditional plasterwork, can offer smoother finishes, and has higher impact resistance.

These properties, as well as others, are often the defining factor in contractors and architects choosing to use GRG in their work. Many even consider the material to be an ideal alternative to other forms of plaster, particularly if they are attempting to undertake complex projects.


What is the Difference Between GRG, GRP, and GRC?

While GRG is an initialism of glass reinforced gypsum, GRP and GRC each have their own unabbreviated names as well: glass reinforced plastic and glass reinforced concrete. These are different to GRG, in that they have their own material properties, beneficial qualities, and spaces in which they are most often used. We have provided more detail on these below:



Glass reinforced plastic (GRP), more commonly known as fibreglass, has a larger range of everyday uses than GRG and is, therefore, more widely known as a building material. Like GRG, GRP is a composite material. However, unlike GRG, GRP is mostly made of glass fibres for which the material is often nicknamed and is best known. These fibres are then impregnated with polymers such as resin to keep it strong and to offer durability.

While GRG is ideal for completing the finishing touches of interior spaces, GRP is more often used in construction, particularly for the manufacture of roofing, canopies, and doors. It is often used as a material alternative to wood or steel.

grp moulding fiberglass column



Glass reinforced concrete (GRC), otherwise known as glass fibre reinforced concrete (GFRC), is also a composite material. Unlike GRG, it uses concrete strengthened with glass fibres to give the material its durability. It is often used for ornamental purposes (including for the construction of fountains) and, also unlike GRG, can be used in exterior spaces. As it can be used outside, it will often be manufactured for the express purpose of creating building façade panels, or for use as architectural precast concrete.

we use Jesmonite AC730 to manufacture a range of GRC products, such as internal and external cladding, design features and decorative enrichments.

Jesmonite AC630 moulding

What are the Material Properties of GRG?

The physical material properties of glass reinforced gypsum (also called its characteristics) are written as follows:

Shell Thickness: ¼” Nominal Standard (+/-⅛” / Unit) [6mm (+/-3mm] {½” min. at edges}

Glass Fibre: 6% min. (by Weight) (Volumetric measurements not valid)

Weight: 1.5 ‒ 2.0 (lbs/ft²) [7 – 10 (kg/m²)] (varies with embedment/reinforcement)

Strength: Flexural: Modulus of Rupture (MOR) 3200 ~ 3500 (PSI) [22 – 24 (Mpa)], Flexural

Modulus of Elasticity: 1.3 ~ 1.9 x 10⁶ (PSI) [1.3 – .9 x 10⁷ (kPa)]

Ultimate Tensile (UTS): 1800 ~ 2000 (PSI) [12 – 14 (Mpa)]

Modulus of Elasticity: 2.7 – 3.8 x 10⁶ (PSI) [1.9 – 2.6 x 10⁷ (kPa)]

Comprehensive Strength: 7200 – 8300 (PSI)

Thermal Conductivity: 4.0 – 4.2 (BTU/in/hr/ft2 /°F) [22.7 – 23.8 (W/m2 °C)]

Thermal Expansion Coefficient: 8 x 10-6 (in/in/°F) [14 x 10-6 (mm/mm/°C]

Fire: ASTM E84-80 (Incombustible Building Material) Flame, Fuel = 0, Smoke = 0

Toxicity: (NBS Certification MEA 42-82) = 0

Density: (Dry) 105 – 114 (PCF) [1680 – 1826 (kg/m3)]

Hardness: 95 RH (min.) (Rockwell Scale)


Tolerances of GRG include:


Dimensional – all directions +/- 1/8”
Warpage or Bowing +/- 1/16” /foot
Square / Skew /Diagonal +/- 1/8” in 10’
Out of Round +/- 1/16” / foot of diameter

Humidified Deflection: 1/8” max (Industry standard)


What are the Benefits of Using GRG?


There are many benefits that come with choosing to use glass reinforced gypsum, rather than other plaster mouldings, in order to complete your work projects. Most of these are to be found in their material properties, including their high strength, high density, and lightweight.

The high strength and surface hardness offers fantastic durability to the product once it has been installed, while its flexibility during the moulding process also means it is easy to handle. This allows for the creation of practically any shape or design in a short amount of time and a cost-effective manner. Being lightweight, the material also offers a faster, less-labour intensive installation, which reduces the costs involved with completing the work.

GRG is also a Class 0 fire rated material, meaning that it is completely fire retardant. This offers your finished interior space extra fire protection, in a material that can be fitted to accommodate alarms, cameras, sprinklers, lighting, and any other features required by the architect to complete their designs and adhere to health and safety guidelines.

Glass reinforced gypsum is also easily dressed and decorated to match most design concepts requested, including being painted in a range of styles and colours to replicate certain natural materials and textures.


For Professionally Manufactured and Installed GRG Products


If you have been considering your options for materials to complete an architectural project and you’ve come across glass reinforced gypsum as a possibility, contact our offices today. We will be glad to discuss everything you need in the way of GRG products and can soon assist you with placing an order for the pieces that will offer the interior finish you have been looking for.

We are a UK-based manufacturer of GRG, which means you can guarantee a product that will be delivered on time and installed to fit your schedule. There will be no delays in shipping and you should not expect any overly detailed paperwork as part of the process.

To see examples of how we’ve used glass reinforced gypsum to complete work for other architects across the country, please see our Projects page.

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