I currently manufacture fiberglass (FRP). Can I use the same glass fiber for GFRC?

No. The standard E-glass fiber used in FRP is not alkali resistant.  The high alkalinity of Portland cement in GFRC will degrade E-glass fiber over time, resulting in reduced strength and durability.  GFRC requires the use of AR glass fibers, which contain a minimum of 16% zirconia.  Some glass fibers labeled as AR contain less that 16% zirconia and should not be used.

Disclaimer
This FAQ article is offered as a guideline and offers possible solutions to problems encountered during mold making and casting. No warranty is implied and it is up to the end user to determine suitability for any specific application. Always refer to the provided Technical Bulletins (TB) & Safety Data Sheets (SDS) before using any material. A small scale test is suggested to determine suitability of any recommendation before trying on a larger scale for any application.