Material guide
Gluing GRP / fibreglass
Glass fibre in cured resin, used for boat hulls, body panels, roofing and enclosures.
Also called composite, fiberglass, fibreglass, glass reinforced plastic, GRP.
How GRP / fibreglass behaves when you bond it
Moulded GRP usually carries release agent from manufacture, and that has to be removed before anything will hold. Once abraded back to a clean matte surface it bonds well, which is why structural repairs to GRP are routine.
GRP is glass fibre embedded in a cured thermoset resin, commonly polyester, vinyl ester or epoxy. Adhesion depends on the exposed resin, gelcoat, weathered layer and mould-release contamination rather than on the buried glass fibres.
Material properties
- Surface energy
- Medium
- Porosity
- Semi-porous
- Rigidity
- Rigid
- Maximum service temperature
- 100C
- Normally needs abrading
- Yes
- Normally needs a primer
- No
- Recommended abrasive grit
- 80 grit (WEST SYSTEM epoxy preparation for polyester laminates after compatible wax/silicone removal.) Manufacturer verified
Surface preparation
Wash off wax, silicone and mould release with a compatible remover before sanding. WEST SYSTEM specifies sanding polyester laminates with 80-grit to a dull finish for its epoxy process. Vacuum and solvent-clean residue, keep fibres intact and repair any delamination before bonding.
Which adhesives work on GRP / fibreglass
Excellent
Two-part epoxy
Two-part epoxy is rated excellent for this material as an application-level assessment, not as a blanket manufacturer claim. The prepared surface must be sound and consistently keyed where the finish permits. Suitability still depends on the other substrate, joint design and service environment.
Abrade the surface first.
Good
Polyurethane adhesive
Polyurethane adhesive is rated good for this material as an application-level assessment, not as a blanket manufacturer claim. The prepared surface must be sound and consistently keyed where the finish permits. Suitability still depends on the other substrate, joint design and service environment.
Abrade the surface first.
Good
Structural acrylic
Structural acrylic is rated good for this material as an application-level assessment, not as a blanket manufacturer claim. The prepared surface must be sound and consistently keyed where the finish permits. Suitability still depends on the other substrate, joint design and service environment.
Abrade the surface first.
Bonding GRP / fibreglass to something else
GRP / fibreglass to Aluminium
GRP / fibreglass to Glass
GRP / fibreglass to Glazed ceramic
GRP / fibreglass to GRP / fibreglass
GRP / fibreglass to MDF
GRP / fibreglass to Mild steel
GRP / fibreglass to Painted metal
GRP / fibreglass to Plywood
GRP / fibreglass to Stainless steel
Last reviewed 8 October 2026.