INTRODUCTION TO GFRG (Glass Fiber Reinforced Gypsum, GFRG, FRG)


This is an introduction into the exciting world of Glass Fiber Reinforced Gypsum (GFRG), also referred to as Fiberglass Reinforced Gypsum (FRG) and Glass Reinforced Gypsum (GFRG). Since its introduction, GFRG has become extremely popular among the Interior Design industry. Along with popularity came concerns about the quality of the material. To eliminate these concerns, Stromberg compiled this information to better educate those interested in GFRG.

HISTORY OF THE PRODUCT

A new concept of material was brought from England to the United States and Canada in 1977; A product now known as Glass Fiber Reinforced Gypsum. This included gypsum plaster reinforced with glass fibers to produce a thin, lightweight, yet strong material.

Before long, North American manufacturers began promoting and selling products produced with GFRG. By late 1978, GFRG jobs were being sold and installed in North America. In the early 1980's, Stromberg developed many of the techniques and technology used in GFRG.

Throughout the 1980's, manufacturers began promoting this material to architects and designers with many selling points. To list a few:

GFRG holds superior fire retardant properties.

GFRG offers a variety of shapes (similar to what plaster and precast offer).

GFRG is lightweight.

Composition- GFRG is composed of:

Gypsum- a hard mineral

Glass Fibers- to provide tensile and flexural strength

Polymers- to improve toughness

Applications

GFRG is for use where it is not subject to dampness. (Do not use where it is openly exposed to rain or for fountains, pools or wet locations. For these applications see GGFRP).

GFRG can be used wherever a light, strong and fire retardant material is required (ships, casinos, hotels, theaters, residential, etc.)

Mouldings, ceilings, columns, light covers are all good candidates for GFRG

Advantages

GFRG (Glass Fiber Reinforced Gypsum) is a composite of glass fibers, alpha gypsum and polymers. It offers several advantages as a construction material.

1) GFRG is a mineral and will not burn. In addition, the nature of gypsum acts like a thermal regulator when exposed to flame. GFRG not only will not burn, but it also protects the materials behind it from the heat of the flame for up to two hours.

2) Installation- GFRG is relatively light in weight compared to traditional stone or plaster ornaments. Its installation is quick and relatively easy.

3) GFRG can be cast to virtually any shape. We supply GFRG columns, GFRG Bas Relief, GFRG domes, GFRG capitals, GFRG fireplace surrounds, GFRG moldings, GFRG medallions and all types of custom GFRG shapes.

4) Finish- GFRG is available in a white color and is easily finished with virtually any paint.

FABRICATION OF THE PRODUCT

GFRG is primarily composed of two raw materials: high density alpha-based gypsum and glass fiber reinforcement. The gypsum plaster should be neutral or of low alkalinity to ensure its compatibility with "E" glass fibers. Additives commonly used within the plaster industry are acceptable provided they are used in accordance with the gypsum manufacturer's recommendations.

PRODUCT TESTING CRITERIA

Most GFRG manufacturers have run tests which determine specific values for properties of glass reinforced gypsum. The following are recommended tests to determine physical properties of GFRG composites:

  • Physical Property Recommended Test Method
  • Surface Burning ASTM E 84-87
  • Characteristics
  • Impact Resistance ASTM D256-87
  • Flexural Strength ASTM C947
  • Compressive Strength ASTM C109-87
  • Hardness ASTM D2583-87 (Barcol) or ASTM D785 (Rockwell)
  • Thermal Expansion ASTM D696
  • Humidified Deflection ASTM C473

Manufacturer's test samples should be representative of actual production procedures and materials. Tests conducted by raw material suppliers or others should detail the procedures and processes used in the preparation of the test samples. The GFRG manufacturer should certify that the material is produced as tested. Test results vary from manufacturer to manufacturer, and it is the specifier's responsibility to evaluate and compare the test results in relation to individual job requirements.

FABRICATION

GFRG products are custom made thin plaster shell shapes and forms manufactured in a plant by either one of two methods, both of which center around how the glass fiber reinforcement is introduced into the product. One method, known as the hand lay-up method, simply means that once the molds have been made and are ready, various layers of continuous glass fiber mat and gypsum are manually placed during the "lay-up" process. Another method, the "chopped-strand-spray" method, introduces glass fiber strands into the plaster mix as it is being sprayed into the mold. Both methods will produce high quality products.

GFRG products are made in molds which are customized for a particular job or from the manufacturer's standard line of molds. Molds should be manufactured in a manner so as not to adversely affect the finished product with respect to shape and finish. The molds should be fabricated to exact dimension and shape specified by approved shop drawings.

After the gypsum and glass fiber reinforcement have set, the product should be carefully removed from the mold and stored until adequately cured for shipment. Due to the nature of the gypsum product, caution and care must be exercised to ensure that the GFRG retains its designed dimensions and shapes. The product must be stored and handled in a manner to prevent warping, bowing, or damage.

TOLERANCES

Fabrication tolerances may vary depending on shape, particular uses, desired finishes, and condition of completed lighting requirements. Generally speaking the product should be fabricated to a tolerance suitable to each particular component.

All manufacturer's tolerances should be expressed in fractions of an inch or metric equivalent. Measurement of any length or any dimension given on the shop drawings should be:

  1. Straightness - at any point on a line generally along a plain, an edge, or a surface, the material should not vary from straight + __or - __.
  2. Overall Length +___ or - ___.
  3. Dimensions within the overall length + __ or - __.
  4. Dimensions width + __ or - __.
  5. Dimensions within the overall width + __ or - __.
  6. Dimensions of chords, radius, diameters + __ or - __.
  7. Measurement of dimensions not given or drawings such as square + __ or - __.

Tolerances should be shown on shop drawings. Next to any dimension where tolerance is critical, it should be marked with a "T".

DESIGN CRITERIA

An understanding of basic moulding and casting constraints as well as standard tolerances, will provide a better understanding for the architect and engineer of design shapes and forms to be manufactured. Here are some design considerations that may affect the cost of GFRG used in your project:

  1. The amount of detail. GFRG can reproduce intricate details or smooth sweeping curves. Details and undercuts require rubber mold liners. Simple smooth flats and curves can be cast in rigid molds of fiberglass. While rubber molds are slightly more expensive, the cost may be minimal if the casting is repeated several times.
  2. Number of repetitive pieces. Numerous casts of a GFRG shape are more economical per piece, than one-time-only casts.
  3. Size. GFRG can be cast in pieces up to 28' in length. The longer the length, the more difficult it is to handle and ship the GFRG casting. We recommend a maximum length of 12' for most moldings. If longer lengths are required, pieces can be field joined in a seamless manner. Contact us for GFRG jointing details.
  4. Surface Finish. The lowest priced finish is usually a plain smooth GFRG. It is generally finished with a flat latex paint. If you intend to use a gloss finish, the GFRG will need some field priming and prep work.
  5. Special Reinforcements. Some specific design considerations are corners, draft angles, reveals, and finishes. All GFRG corners should have a radius of between 1/16" and 1/8" unless otherwise noted.

Draft Angles and Reveals
Draft angles are designed bevels which allow the mold to release the GFRG parts and/or pieces. Reveals incorporated in a design should have draft angles present.

Finish
In general, standard GFRG products, as cast, do not have surface characteristics required for a high gloss finish. In most cases, the surface can be adequately prepared in the field to receive high gloss paint through the use of compounds, sealers, and/or primers. Before specifying or purchasing GFRG (GFRG, Glass Fiber Reinforced Gypsum), specific information about the surface finish should be determined. Any special finish, such as gloss, which demands a more stringent requirement, should be specifically pointed out in the design process. Many GFRG products can be pre finished.

SHIPPING

There are two common means of shipping and transporting the finished GFRG products. The first is to crate every piece of GFRG in a "wooden box or form" and ship the entire "package" to the jobsite. The second way eliminates "crating" and utilizes air-ride suspension trailers and trucks. Regardless of how it is shipped care and caution is used to ensure the product arrives at the jobsite in good condition. In overseas shipments, the GFRG is wrapped, crated and shipped by container.

FIELD CHECKING MEASUREMENTS

Listed below are four categories for field checking measurements of GFRG. First are the tools required for taking the measurements and then the actual method of checking.

1) For Straightness:

Tools Required: Using a string line and ¼" shims or equivalent; an absolutely flat surface is also acceptable.

Method: To check for straightness, place string line and shims over surface to be checked. Use a ¼" shim at 1 foot intervals to determine any variation from straight that occurs. Measure this variation if it appears to be greater than tolerance with a folding rule having at least 1/16" marks on it. Do not check in tapered edges.

2) For Chords and Lengths:

Tools Required: Use standard tape measure.

Method: To check for chords and lengths, use a standard tape measure. Use a block to determine the edge or corner. "Tapered" edges must be considered when establishing the measurement. Shop drawings should indicate whether they have been calculated or not. If "tapered" edges are not included in calculations, then a point or edge must be created by a block or other means to measure to and from.

3) For Curvatures:

Tools Required: Use a cardboard or hardboard template. Template should be cut ¼" larger than dimensions if it is outside radius or ¼" smaller than dimensions for an inside radius.

Method: To measure from a template, cut a piece of cardboard (or hardboard if many measurements are to be made) ¼" larger or smaller than the desired shape and use a ¼" x ¼" shim to check the dimension of the shape. Do not measure or check in "tapered" edge portion of the material. If deviation from the shape dimensions exist, then measure with a folding rule with 1/16" marks on it.

4) For Squareness:

Tools Required: Use a tape measure or a layout on a flat surface.

Method: To measure for a square, a corner to corner measure should be taken if possible. If corner to corner is not appropriate, lay out on a flat surface, the shape of the part and use squares to determine the measurements.


JOBSITE INSTALLATION


Receiving and Storage of Materials

Once the product has been fabricated and shipped properly to the jobsite, the installer must, upon receipt, inspect and store the product correctly to avoid warping, twisting, or bowing. All pieces, crates, or cartons should be carefully examined for visible damage at time of receiving. Any visible defects must be noted on the bill of lading at the delivery site and Stromberg should be notified. Upon receipt of the product , the GFRG must be placed on a level surface in an upright position. Individual parts and pieces should never be stacked on top of one another. GFRG products should be stored and installed under favorable jobsite conditions similar to those required for drywall.

Installation Procedures

Using shop drawings and Stromberg recommendations of, GFRG components should be installed plumb and level to required planes as designed and indicated. Minor configuration changes can occur and can be adjusted by wetting and fitting the pieces or parts.

If attachments to a framing system is required, it should be by screws, adhesive, or hanging in accordance with manufacturer's recommendations. All FRG assemblies should have no deflection greater than L/240.

Openings for plumbing, electrical and mechanical penetrations may be field cut using methods, tools and procedures within drywall construction. Repairs to Glass Reinforced Gypsum components can generally be accomplished by using standard drywall or plaster materials.


Auxiliary Materials

In addition to the basic materials in all Glass Fiber Reinforced Gypsum products, materials necessary for proper installation vary depending on the project. The list of materials range from conventional drywall screws to stainless hanger wire and depends greatly on the particular application. The most common materials used in joining and supporting GFRG are as follows:

  1. Steel studs, runners, and custom shapes made from sheet metal for alignment and attachment of GFRG
  2. Bolts and various screws as necessary for attachment of framing members and GFRG component attachment.
  3. Adhesives as required for bonding GFRG panels together and to the substrate.
  4. Primary suspension members for GFRG ceilings such as 1-1/2" and ¾" cold rolled steel channels-galvanized or painted.
  5. Wire, rod or strap hangers, power-actuated eye pins, drilled-in anchors, inserts, and other suitable hanger attachment devices used in typical ceiling applications for support.
  6. Blocks and shims as necessary for attachment or alignment of GFRG products.
  7. Tape and joint compounds of the type used for drywall fin

Joints

Since many GFRG products will be judged in their "monolithic" smoothness of appearance, the joints and treatment of the joints are critical. The designed and installed joint should have a joint alignment tolerance not to exceed 1/8" and joint width not exceed 3/8". Joint finishing should be performed in accordance with ASTM C840. The completed joints and seams should provide a smooth and continuous surface. Control joints may be a matter of aesthetic considerations, however, these should never exceed recommended spacing.

Erection Tolerances

It should be the contractor's responsibility to ensure that all components of the FRG system are installed reasonably level, plumb, straight, or curved as designed and specified. All lines, planes and joints should be uniform and comply with following the tolerances:

Plane alignment (panel to panel) 1/16"
Variation from plumb + or - 1/8" per 10 ft.
Variation from straightness + or - ¼" per 25 ft.


Quality Assurance

The success of any GFRG system depends on a coordinated effort by the designer, manufacturer and installer. Sequence, deliveries and manufacturing tolerances are critical to the success of the project and should be mutually agreed upon by all parties. Submittals and shop drawings should be utilized extensively to familiarize the designer and installer with the method of attachment, reinforcement and fabrication. This process alerts the designer to any possible conflicts. The shop drawings should be complete in every detail to allow the installing contractor a complete inventory of parts and pieces, as well as expected tolerances.

Conclusion

A properly designed, manufactured and installed GFRG system will provide an innovative and aesthetically pleasing interior while often reducing overall cost, onsite labor requirements and shortening construction schedules. The GFRG offers an endless variety of decorative and ornamental shapes and forms at affordable prices.