The properties of Glass fiber Reinforced Concrete (GFRC) vary according to the production method, mix design, and the type and content of the Alkali Resistant (AR) Glass fiber.
- Traditional Hand Spray can produce the highest strengths due to a high AR Glass fiber content, low water/cement ratio, long fiber length and planar fiber orientation.
- Cast Premix strengths are generally lower than those of the Traditional Spray method due to lower AR Glass fiber reinforcement contents, higher water/cement ratios, shorter fiber lengths and 3-dimensional fiber orientation.
- Sprayed Premix gives consistent mechanical properties similar or higher than those obtained with vibration cast premix.
Cast Premix As the name suggests the glass fiber is mixed into the cementitious slurry and the resulting material is poured or pumped into moulds and compacted using vibration or by using special additives in the mix. Self Compacting Cast Premix GFRC as the name implies, is a special GFRC mix which can be poured into moulds and compacted without the need for any further mechanical intervention (e.g. vibration).
The premix process can be easily automated and is often chosen for standard product manufacture. The moulds used are more complex than those for the spray process. The mechanical properties are lower but they are consistent allowing optimum design.
Hand Spray is the most versatile and popular production technique and the one normally chosen by new start-ups. A special spray gun is used to simultaneously deposit chopped glass fiber and cementitious slurry onto a mould. This is then compacted by hand using a spring roller. A second layer is then sprayed and again compacted. Using the spray technique allows high glass percentages to be used and this gives the highest mechanical properties. In turn this allows for reduced skin thickness and lighter products.
Auto Spray The hand spray process can be automated or semi automated. More common are semi-automatic processes where the spray gun is mounted on a reciprocating traverse with the moulds passing underneath on a conveyor. Compaction can be by hand or via a de-watering system. These systems are ideal for the production of flat products and they can also be very versatile when used with folding moulds.
Sprayed Premix This is a combination method where the premixed material is sprayed onto the mould. It combines the advantages of both the Hand Spray and Cast Premix methods and is becoming the method of choice for many small architectural items.