The Flat Roofing Shop
C3 GRP External Wall Fillet Corner
C3 GRP External Wall Fillet Corner
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Pre-formed fibreglass corner for neat external wall-to-wall and upstand junctions
The C3 GRP External Wall Fillet Corner is a hot-pressed, pre-formed fibreglass corner designed for use where two wall fillet trims meet at an external 90° corner.
It is commonly used at external wall junctions and at the base corners of skylight and rooflight upstands, creating a clean, uniform finish without the need to mitre or hand-form trims on site.
Compatible with D260 fillet trim profiles.
What It’s Used For ▸
- Forming external 90° wall-to-wall fillet corners
- Creating neat base corners on skylight upstands
- Joining D260 fillet trims at external junctions
- Replacing site-cut mitred fillet corners
Designed specifically for GRP roofing systems where detail quality and consistency matter.
Why It Matters ▸
External fillet corners are high-visibility and high-movement areas within a GRP roof system.
Hand-cut mitred fillet trims can:
- Look uneven
- Create inconsistent angles
- Take longer to install
- Require additional finishing
A pre-formed C3 corner:
- Speeds up installation
- Ensures consistent 90° geometry
- Delivers a cleaner, more professional finish
Once laminated and top coated, it produces a seamless and professional external junction.
Installation Overview ▸
- Position the C3 corner and mechanically fix to the deck (each end and centrally).
- Apply a thin bead of PU trim adhesive at trim junctions.
- Fit adjoining D260 fillet trims into place.
- Bandage the joint using taping mat and wet out with base resin.
- Use finishing tissue if required for a smooth edge.
- Top coat as part of the GRP system.
Ensure all surfaces are clean and dry prior to bonding and laminating.
Technical Specification ▸
Type: C3 External Wall Fillet Corner
Material: Hot press moulded GRP
Compatibility: D260 Fillet Trim
Use: External wall-to-wall fillet junctions and upstand base corners
Roofer’s Perspective ▸
External wall corners and skylight bases are where messy mitres show up. A moulded C3 corner keeps the junction sharp and uniform without having to cut and shape fillets on site.
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