The spray-up process is an open mould composite manufacturing technique where chopped fibers and resin are simultaneously sprayed onto a mould to form laminates. Closely linked to technical textiles, it uses fiber reinforcements as structural elements, combining textile engineering (fiber type, length, orientation) with polymer processing to produce cost-effective FRP components.
Step By Step Guide
- Mould Preparation: Clean mould, apply release agent and gel coat
- Spraying: Chopped fibers and catalyzed resin sprayed using chopper gun
- Compaction: Rollers remove air and improve bonding
- Layer Build-Up: Repeated spraying to achieve required thickness
- Curing: Ambient or heat curing to solidify laminate
- Finishing: De-moulding, trimming, and surface finishing
Material Used
Fibers (Reinforcements):
- Glass fiber (E-glass chopped strands – most common)
- Carbon fiber (high strength, lightweight)
- Aramid fiber (impact resistance)
Forms:
- Chopped strands (primary)
- Continuous roving
- Woven fabrics / stitched mats (hybrid reinforcement)
Resins:
- Polyester (widely used)
- Vinyl ester (corrosion resistance)
- Epoxy (high performance applications)
Advantages
- Low tooling cost (open mould process)
- Faster than hand lay-up
- Suitable for large and complex shapes
- Flexible and adaptable manufacturing
- Reduced labor due to semi-automation
Limitations
- Lower mechanical strength (random fiber orientation)
- High resin consumption → heavier parts
- Limited control over fiber alignment
- Rough surface finish on inner side
- Health & environmental concerns (overspray emissions)
Industries:
- Marine
- Construction
- Automotive
- Sanitary ware
- Chemical processing
- Energy sector
End Products:
- Boat hulls and decks
- FRP tanks and silos
- Bathtubs and sanitary units
- Automotive body panels
- Enclosures, ducts, and housings
Selection Criteria
Select Spray-Up When:
- Large and simple geometry components
- Cost-sensitive production
- Moderate mechanical performance required
- Faster production needed
Avoid When:
- High structural strength or precision required
- Controlled fiber orientation is critical
- Aerospace-grade performance needed