Cem-FIL® fibers enable manufacturers to produce thin (10mm or1/2 in), strong concrete with improved finishes and greatly reduced weight - as little as 1/8th of the weight of the equivalent concrete product.

When 2 to 5% of Cem-FIL® fibres are mixed into a simple 1:1 cement:sand and water matrix, a thin but strong form of concrete is produced - GRC (or GFRC). GRC has a high compressive strength along with good tensile and bending properties so products can be designed in thin (10mm or 1/2 in) sections.

Raw materials:
Material Content
Cem-FIL® Glass fiber reinforced cement uses the following raw materials:
- Cem-FIL® Alkali Resistant fiberglass formed into continuous strands or rovings, or pre-chopped strands, either loose or bonded into a mat for hand lay-up.
- Ordinary Portland Cement, white or grey. (If rapid demolding, 1 to 1 1/2 hours, is needed, special cements can also be used).
- Clean, dry and graded sand.
- Acrylic polymer in emulsion form for curing (optional for many products).
- Superplasticizer, to improve the workability of the mortar, and to improve the composite's strength.
- Water

Cem-Star Metakaolin may be also be added as partial cement replacement materials to improve the long term properties of the GRC.

Mold or forms
The appearance of the finished product is directly related to the form material and the quality of the mold itself.
They can be made from various material such as:
- Steel
- Plywood
- Plastic
- Rubber Molding Compounds
- FRP (Glassfiber reinforced polyester resin)
- GRC itself
A combination of materials is frequently necessary in order to give the desired stiffness, shape and surface finish.
For complicated details, molds of plastic, rubber, foam or sculptured sand may be used. Mold material and construction should not allow warping or buckling to occur and should be non-absorbent.
All corners should have fillets, chamfers or rounded corners and mold release compounds to match the mold material being used.
Mixing instructions Manufacturing equipment is available from SprayTech for USA and Middle East and K&C Mouldings for Europe and Far East.
Mortar mix It is first necessary to prepare a 'creamy' mortar mix by blending the cement, sand, water and plasticizer together using a mixer with a high shear action. A conventional concrete mixer can be used but it will take longer.

Blending in the Fibre Once the mortar mix is made, the fibres are then added. Depending on the production process being used, 3 basic techniques of fibre incorporation are used:
- Premix, using pre-chopped 12 to 40mm (1/2 to 1 5/8") fibre
- Spray process with purpose built equipment and continuous rovings of fibre
- Hand lay up using a chopped strand mat or woven filament net

Premix
The 12 to 40mm (1/2 to 1 5/8") chopped strands are stirred into the mix at low speed, until they are dispersed with no dry clumps visible. This normally only takes 1 to 2 minutes. Over mixing should be avoided once the fibre has been added. The mix will look stiff but can be easily cast, with vibration into molds.

Spray The continuous strand is fed into a chopping gun, cut to 25 to 37mm (1 to 1 1/2") and simultaneously sprayed out with the cement mortar. The cement mortar is fed to the spray gun by pump, and is atomised by the spray gun using compressed air. The glass fibers and cement mortar are sprayed together onto a prepared mold where they are compacted to product the composite GRC using rollers. The strands will be orientated in 2 dimensions.
Hand Lay-Up
The mortar mix is sprayed or painted onto the mold or form and the chopped strand mat or net laid on. The mortar is then forced through with the brush or a compaction roller. Excellent mechanical properties are achieved and no special equipment is needed. Finishes
There are four basic finishing techniques: Mist Coats, Face Mixes, Veneers and Coatings.

Mist Coats A smooth or light textured off-the-form finish usually made from colored sands, crushed natural aggregates or stones, with or without pigments, mixed with white cement unless a dark color is specified. A 3 mm (1/8 in). thick mist is sprayed into the form before the GRC is applied. The mist coat and the GRC matrix are usually the same formulation. Imitation natural slates and stones and terra cotta can be accurately imitated by this technique. The appearance can be enhanced by acid etching or light abrasive blasting after demolding
Face mixes Up to 12mm (1/2 in.) thick and laid into the mold before the GRC backing is applied. The mix consists of sand, course aggregates, from 1 to 10mm (3/16 to 3/8 in), and pigments, if required, to get the desired color. The face mix characteristics should match closely those of the GRC matrix to reduce differential movement. The facing mix is usually exposed by using chemicals such as retarders placed on the form first or by acid etching after demolding. Mechanical exposure through abrasive blasting or honing and polishing is also used.
Coatings GRC is a dense, smooth surface and coating manufacturers should be consulted. The surface should be lightly sand blasted or acid etched to improve adhesion and should be of the 'breathing' type. Typically, latex or fluorene coatings (e.g. Covema) are suitable for exterior applications.

Veneers
A highly skilled technique whereby natural cut stone, thin brick or architectural terra cotta are mechanically fixed to the face of the GRC during production. Expert advice should be sought