For use in the formation of bay window sills.

This mix can also be used in a number of different forms including copings, columns and garden features - consult manufacturer for details.

Please note, this mixture is not suitable for large sections or cladding panels.


Glass fibre reinforced concrete premix, for the formation of bay window sills.

Features and benefits:

  • Offers higher flexural strength properties than other architectural dressings and decorative features produced using traditional semi-dry or wet cast production methods.
  • Can be produced into a range of bespoke shapes and sizes.
  • Fire-resistant.
  • Lightweight.
  • Offers higher flexural strength properties than traditional semi-dry or wet cast concrete
  • Offers increased impact resistance and high durability due to the reinforcing fibre distributed throughout the matrix.
  • Available in a range choice of three colours.
  • Meets/ exceeds the GRCA Specification 'Specification for Manufacture, Curing and Testing of GRC'.
  • Manufactured under a BSI accredited Quality Management System to ISO 9001: 2015.
  • Full UKAS accredited testing to ISO 17025: 2017.

General information


Range of three colours.





Highly cement based composite manufactured from white cement, silica sand, admixtures and additives reinforced with alkali resistant glass fibre.


Can be produced to bespoke shapes/ designs


Can be produced to bespoke sizes

Uniclass 2015

Pr_25_93_52_33 Glass-reinforced concrete (GRC) bay window sillsPrimary


H40/120 GRC components

H40/130 Proprietary GRC components

Specification data - Glass-reinforced concrete (GRC) bay window sills Enhanced data


GRCA Specification for the manufacture, curing and testing of glass fibre reinforced concrete (GRC) products.

Production method

Premix process in accordance with GRCA Specification 2017.

Guide mix design

Grade 8P.


Insert requirements.

Sill type

Insert requirements.

Masonry facing type

Insert requirements.



Height (overall)

Insert requirements.

Masonry bay side length (external)

Insert requirements.

Masonry bay width (external)

Insert requirements.

Length of slip sill for side of bay

Insert requirements.

Length of slip sill for front of bay

Insert requirements.

Exposed faces


Surface texture

Insert requirements.





Applied surface finish


Product Reference

Premix GRC Bay Window Sills

Flexural strength

After 28 days (LOP): 5 MPa. After 28 days (MOR): 8 MPa to EN 1170-5.

Dry density

1850 kg/mᶟ to EN 1170-6.

Water absorption

9% to EN 1170-6.


Premix GRC

Premix GRC

Syntec GRC Company Brochure

Syntec GRC Company Brochure

Third party certifications

  • GRCA: Full Member Certificate: 1097/32